Naval Submarine Medical Research Laboratory 

 NSMRL Report 1213 10 September 1999 

EFFECTS OF A PROLONGED 

SUBMARINE DEPLOYMENT ON 

SPECIAL OPERATIONS FORCES 

MISSION-RELATED PERFORMANCE 

by 

J. R. SIMS, D. M. FOTHERGILL, and C. L. SCHLICHTING 

Released by 

M.D. Curley, CAPT, MSC, USN 

Commanding officer 

Naval Submarine Medical Research Laboratory 

Approved for public release; distribution unlimited
Naval Submarine Medical Research Laboratory 

Box 900, Groton, CT 06349-5900 

Tel: 860 694 2536 

 NSMRL Report 1213 10 September 1999 

EFFECTS OF A PROLONGED SUBMARINE 

DEPLOYMENT ON SPECIAL OPERATIONS FORCES 

MISSION-RELATED PERFORMANCE 

By 

J. R. SIMS, D. M. FOTHERGILL, and C. L. SCHLICHTING 

Approved and Released by: 

M. D. CURLEY, CAPT, MSC, USN 

Commanding Officer 

NAVSUBMEDRSCHLAB

fc$. &*&£^
2 

TABLE OF CONTENTS 

TABLE OF CONTENTS............................................................................................................................................ 2 

EXECUTIVE SUMMARY......................................................................................................................................... 4 

INTRODUCTION....................................................................................................................................................... 5 

METHODS .................................................................................................................................................................. 5 

PRE-DEPLOYMENT AND POST-DEPLOYMENT MEASURES ........................................................................................... 5 

Cooper Test........................................................................................................................................................... 5 

Physical Test Battery ............................................................................................................................................ 6 

Cognitive Test Battery........................................................................................................................................... 7 

VARIABLES STUDIED THROUGHOUT STUDY PERIOD ................................................................................................... 7 

Activity Levels ....................................................................................................................................................... 7 

Mood States........................................................................................................................................................... 9 

Physical Health Symptoms.................................................................................................................................... 9 

Sleep-Wake Cycle.................................................................................................................................................. 9 

Caloric Intake ....................................................................................................................................................... 9 

Ambient berthing noise ......................................................................................................................................... 9 

Submarine atmosphere.......................................................................................................................................... 9 

Data Analyses ..................................................................................................................................................... 10 

RESULTS .................................................................................................................................................................. 10 

COOPER TEST .......................................................................................................................................................... 10 

SHOOTING................................................................................................................................................................ 14 

HAND-GRIP STRENGTH............................................................................................................................................ 14 

HAND-GRIP ENDURANCE......................................................................................................................................... 14 

MANUAL DEXTERITY (GUN ASSEMBLY) ................................................................................................................. 14 

STEP TEST................................................................................................................................................................ 16 

PULL-UPS................................................................................................................................................................. 16 

COGNITIVE TESTS.................................................................................................................................................... 16 

ACTIVITY LEVELS.................................................................................................................................................... 18 

MOOD...................................................................................................................................................................... 18 

HEALTH ................................................................................................................................................................... 18 

SLEEP....................................................................................................................................................................... 19 

CALORIC INTAKE ..................................................................................................................................................... 20 

AMBIENT NOISE....................................................................................................................................................... 21 

SUBMARINE ATMOSPHERE....................................................................................................................................... 21 

DISCUSSION ............................................................................................................................................................ 24 

STUDY LIMITATIONS................................................................................................................................................ 26 

POSSIBLE STRATEGIES FOR MITIGATING DECONDITIONING...................................................................................... 30 

CONCLUSIONS AND RECOMMENDATIONS .................................................................................................. 30 

ACKNOWLEDGMENTS ........................................................................................................................................ 32 

COLLABORATORS/CONTRACTORS................................................................................................................ 32 

REFERENCES.......................................................................................................................................................... 33 

APPENDIX A: SELF-REPORT ACTIVITY LOG ............................................................................................... 37 

APPENDIX B: SLEEP QUESTIONNAIRE........................................................................................................... 38 
3 

APPENDIX C: PROFILE OF MOOD STATES.................................................................................................... 44 

APPENDIX D: HEALTH SYMPTOMS QUESTIONNAIRE .............................................................................. 45 

APPENDIX E: WALTER REED ARMY INSTITUTE OF RESEARCH REPORT ON SLEEP PATTERNS 

DURING OPERATION FOAL EAGLE ................................................................................................................ 46 
4 

EXECUTIVE SUMMARY 

Study Objective

Physical exertion is an inherent element in many Special Operations Forces' (SOF) missions. It 

was hypothesized that a SOF unit following a prolonged submarine deployment might have a 

decrement in a variety of physical tasks that require aerobic endurance, anaerobic bursts or 

physical strength. This study was conducted to document how mission-related performance of 

SEAL Team One is affected following a long submarine deployment on SSN 642 Kamehameha. 

Methods

A total of 22 individuals participated over 66 days which included 33 days of deployment for the 

SEAL Team (DST) and 53 days of deployment for the submariner control group (SCG). Another 

control group of 9 members from a non-deployed SEAL Team (NDST) was studied over the 

same time period as the deployed SEAL Team. All subjects performed cognitive and physical 

test batteries immediately before and after deployment. Variables believed to influence missionrelated performance such as activity levels, medical symptoms, mood levels, dietary intake, and 

submarine atmosphere were also monitored over the entire length of the study. 

Results

Results showed between a 3% and 11% (± 95% confidence limits) decrease in the distance ran 

during a 12-min maximal effort run for the DST after deployment (p<0.002). The DST also had 

between a 4% and 15% (± 95% confidence limits) decrease in the number of steps climbed 

during a 1-min step test after deployment (p<0.006). The DST reported exercising 70% less time 

than the NDST over the entire time of the study (p<0.01). There was no significant change in any 

measures of the DST between pre-deployment and post-deployment for maximum grip strength, 

grip strength endurance, manual dexterity, pull-ups, cognition or body weight (p>0.05). There 

were significant increases in medical complaints for sinuses, headaches, backaches, constipation, 

and cuts/sores during the deployment for the DST (p<0.05). Deployment had a significant 

negative affect on mood scores in 9 of the 13 parameters measured for the DST (p<0.05). 

Meanwhile there was no change in mood scores for the NDST. In contrast to the DST the SCG 

showed significant improvements in running performance (p<0.01) and step test performance 

(p<0.05) following deployment. The improved performance by the SCG is likely a result of a 

significant practice effect due to the fact that the SCG were only able to perform the physical test 

battery once prior to deployment. 

Conclusions

In conclusion, a 33-day deployment on a converted ballistic-missile submarine, resulted in 

statistically significant decreases in aerobic and anaerobic performance, as well as increases in 

medical complaints in members of this deployed SEAL Team. It is possible that some of the 

medical complaints may impact Dry Deck Shelter operations (e.g. increase in sinus problems). It 

is unknown to what level the observed degree of deconditioning will impact the SEALs 

performance during an actual mission; however, it can be inferred from the results that missionrelated performance will be most impacted when extended periods of physical exertion and short 

high intensity activity is required. It should be borne in mind that some of the observed 

decrements in performance of the DST may have been due to asynchrony of circadian rhythms 

and the effects of jet-lag resulting from their air flight travel from Korea to Hawaii immediately 

before conducting the post-deployment tests. 
5 

INTRODUCTION 

Physical exertion is an inherent element in many Special Operations Forces' (SOF) missions. 

Troops perform a variety of demanding tasks that require aerobic endurance, anaerobic bursts 

and physical strength. Examples of the physical demands of Sea-Air-Land (SEAL) operations 

are described in Prusaczyk et al., (1995) and include swimming/diving, running, long loadbearing hikes, climbing, and piloting SEAL Delivery Vehicles (SDVs). SOFs typically maintain 

intense physical training regimens to perform these tasks on real-world missions (Barnes and 

Strauss 1986; Prusaczyk et al., 1991, 1994). Concern has been voiced that long transits with SOF 

units on board submarines results in a degradation of their mission-related performance. 

Potential factors that might contribute to poor mission-related performance are physical 

inactivity, alterations in exercise routines, changes in diet or sleep patterns, fluctuations of 

emotional or cognitive states, perturbations of submarine atmosphere and increases of medical 

ailments. Currently, it is uncertain that a decrement in performance exists and if it does, what 

impact any decrement has on operations. We conducted a controlled observational study to 

document decrements in mission-related performance and identify those factors that may have 

the largest influence on the identified decrements. 

METHODS 

The Committee for Protection of Human Subjects at the Naval Submarine Medical Research 

Laboratory, Groton, Connecticut and Naval Medical Research and Development Command, 

Bethesda, Maryland approved the study. All subjects were recruited from SDV Team One and 

the USS Kamehameha SSN 642 in Pearl Harbor, Hawaii. All subjects were informed volunteers. 

A total of 31 subjects participated, 10 members in the deployed SEAL Team (DST), 9 members 

in the non-deployed SEAL team (NDST), and 12 members in the submariner control group 

(SCG). No subject withdrew from the study. The data below were collected on all three groups 

over a two-week period prior to submarine deployment for DST and SCG. The DST underwent a 

33-day deployment then returned to Pearl Harbor by airplane and performed post-deployment 

tests. The NDST performed all ìpost-deploymentî tests two days prior to the return of the DST. 

Post-deployment testing on the SCG was conducted once the submarine returned to Pearl Harbor 

following a total time of deployment of 53 days. 

Pre-deployment and Post-deployment Measures 

Cooper Test

Aerobic capacity was measured using the Cooper Test (Cooper 1968). All subjects performed the 

test on the same outdoor track between 10:00 and 11:00 AM. Subjects ran around the track for 

12 minutes attempting to reach the farthest distance possible. The distance that each subject 

achieved was measured with a rolling wheel tape measure (Road Runner, Model RR-318, 

Keson, U.S.A.). Distance was recorded in meters. Subjects wore a Polar Heart Rate Monitor 

NVô, which recorded heart rate during the run and at least 3-5 min after the run (recovery time). 

The heart rate monitor was set to record the average heart rate (HR) over each 5-second interval 

during the test. Heart rate data was downloaded to a Pentium II IBM ThinkPadô (Operating 

System: Microsoft Windows 95ô) using the Polar Advantage Interfaceô and Polar Precision 

Performance Softwareô version 2.02.004. Both SEAL groups performed two pre-deployment 

runs each separated by one week. The first pre-deployment test enabled the SEALs to gain 

practice in pacing themselves to run maximally for 12 min. It was assumed that any practice 
6 

effects from this first test would not be lost over the study period but would be carried through to 

the post-deployment test. Due to a busy pre-deployment work schedule the SCG only performed 

one pre-deployment run on the day before deployment. All subjects performed one run after their 

deployment period. For the SEAL groups, data from the second pre-deployment test was used in 

all comparisons with the post-deployment data. The dependent variables recorded from each 

SEALís Cooper Test included the distance ran (D), mean exercise heart rate (HRmean), D/HRmean, 

maximum exercise heart rate (HRmax), the slope of the initial heart rate recovery curve (HRrecslope) 

and heart rate recovery time (HRrectime). HRrecslope was derived from linear regression analysis of 

the first 30 s of HR recovery data. HRrectime was calculated as the time for the HR to drop to 70% 

of final exercise HR. Only one subject failed to perform a second pre-deployment Cooper test. 

Data from this subject was still included in the pre versus post-deployment analysis. Three 

subjects in the NDST group were not included in post-deployment heart rate measures because 

their data were lost due to battery failure. 

Physical Test Battery: 

The physical test battery was designed by the Naval Medical Research Institute, in an effort to 

measure SOF mission-related performance (Thomas et al., 1994; Hyde et al, 1997). The battery 

consists of 1) Target Shooting 2) Hand Strength and Endurance 3) Manual Dexterity 4) Step Test 

5) Pull-ups. These tests were performed in the order listed. All subjects, except SCG, completed 

at least two pre-deployment batteries each separated by one week. All subjects completed the 

battery after each groupís respective deployment period. 

The target shooting range consisted of 8 targets evenly spaced over a 180° arc subtended 50 feet 

from the center of the shooter. Targets consisted of three-inch reflectors that were presented at 

predetermined random intervals (2-4 seconds) and remained in the field of view for 

predetermined random lengths of time (2-4 seconds). A total of 48 targets were presented for 

each sequence. A total of 10 sequences were predetermined. No subject practiced or was tested 

on a previously completed sequence. Subjects used a modified M-16 designed to fire a laser 

signal and produce recoil with each trigger pull. Subjects wore double hearing protection to limit 

target detection to visual acquisition. During the pre-deployment period the SEALs were allowed 

to practice the shooting task during their free time. During each supervised practice trial the 

number of shots and the number of hits were recorded. For each SEAL the practice trial with the 

greatest number of hits was used as the pre-deployment score. Only one target sequence was 

used to determine the post-deployment score. 

Left and right hand grip strength and endurance were measured using a proprietary hand 

dynamometer connected to a laptop computer. The laptop computer displayed real-time feedback 

of the force exerted on the grip dynamometer. Hand dominance was recorded. Subjects were 

instructed to squeeze the dynamometer as hard as possible; peak pressure was recorded for 

maximum grip strength. Immediately upon reaching maximum grip strength subjects were 

instructed to reduce their grip force to approximately 50% of their maximum grip strength. Using 

visual feedback of the grip force on the computer screen they were then required to maintain 

their grip force between 45% and 55% of their maximum grip strength for as long as possible. 

The computer determined grip endurance by calculating the total amount of time spent above 

45% of maximum grip strength. Maximum grip strength for statistical analysis was determined 

by taking the best value achieved for left and right hand for pre-deployment. Grip endurance for 

statistical analysis was determined by using the endurance time recorded for the best maximum 

grip strength for both right and left for pre-deployment. 
7 

Manual dexterity was tested using the disassembly and reassembly of an M-16 (Model 727, 

carbine, and 5.56 mm) rifle. Subjects were instructed on the task and allowed to practice as much 

as they wished prior to deployment. Practice was not allowed over the deployment. One practice 

was allowed at post-deployment testing. The average of the total time from start of disassembly 

to completion of reassembly of the rifle for each individualís last two pre-deployment trials was 

used for statistical analysis. 

Anaerobic performance was tested using a modified Harvard Step Test (two steps, each ten 

inches in height, for a total of twenty inches vertical rise) with the addition of a 40-lb. weight 

vest worn during testing. Subjects ascended and descended the stairs as quickly as possible for 

60 seconds. Each cycle up and down the stairs triggered a laser counting beam. The number of 

cycles attained over 60 seconds for the last pre-deployment trial was used for statistical analysis. 

Three to five minutes after completion of the step test, each subject performed a maximum 

number of pull-ups as a measure of upper body strength. The number of pull-ups performed for 

the last pre-deployment test was used for statistical analysis. 

Cognitive Test Battery

This cognitive test battery was designed by the Naval Medical Research Institute, in an effort to 

measure the basic elements of cognitive function thought to be important in SOF mission-related 

performance (Thomas and Schrot, 1995; Thomas et al., 1995). The cognitive test battery is 

performed with the aid of a computer and consists of the following tests: 1) Matching-to-sample 

2) Complex reaction time 3) Visual vigilance 4) Serial addition-subtraction 5) Logical reasoning 

6) Repeated acquisition, in that order. Details of each of these cognitive measures are provided in 

Thomas and Schrot (1995). The total time required to perform all tests was approximately 20 

minutes. We attempted to get each subject to perform approximately six practice sessions during 

the two weeks prior to deployment. Multiple subjects were tested simultaneously using 14 

separate computer stations. Performance on each test is determined by measuring reaction time 

and accuracy of responses. For all of the cognitive tests, the mean score of the final two practice 

sessions pre-deployment was compared to the post-deployment score. One submariner was 

removed from analyses because he completed only one practice session pre-deployment. 

Subjects were removed from analyses if their response times for tasks that required complex 

cognitive processing were equivalent to a simple reaction time response and the number of 

correct responses approached random guessing. No more than two subjectsí responses were 

eliminated from any one cognitive test. Post testing on the DST was conducted on board the 

submarine the day before disembarking in Korea. 

Variables studied throughout study period 

Activity Levels

Activity levels were monitored with self-report logs and heart rate monitors. Subjects recorded 

daily activity on computerized bubble scoring logs (see Appendix A). These logs were filled out 

for six days prior to deployment, three days at the beginning of deployment and for three days at 

the end of deployment. Subjects recorded time spent sleeping, working, exercising, eating and 

doing other activities in half-hour increments. Total time spent for each category, number of 

sleep periods and the longest single sleep period was calculated for each subject. 

The SEALs wore the Polar Heart rate watches for approximately 4 days pre-deployment and for 

8 to 11 days throughout the 33-day deployment period. Scheduling conflicts prevented pre-
8 

deployment heart rate monitoring of the SCG. While underway each submariner wore the heart 

watch for approximately 18 days (range = 9 to 24 days) spread evenly across the submariners 53-

day deployment period. The subjects were instructed to wear the heart watches during their 

waking hours. An attempt was also made to record heart rates during SEAL operations; however, 

after several watch breakages/losses this was abandoned to prevent further loss of equipment. 

Average heart rate over each minute was stored in the Polar heart watch memory and then down 

loaded to a laptop computer at the end of each week. These heart rate data were analyzed offline 

to determine the duration and intensity of exercise performed by each subject. Exercise was 

defined by any period of activity that resulted in the average heart rate attaining 100 beats/min or 

greater for 15 continuous minutes or longer. To account for individual variation in the amount of 

recorded heart rate data, the amount of exercise performed by each subject was normalized by 

dividing total exercise duration by the total amount of time over which heart rate data was 

recorded. Daily exercise intensity for each individual was determined by performing a 15-point 

unweighted moving average on the minute average heart rate data and then calculating the 

average heart rate for the exercise periods based upon the moving average data (see example 

shown in Figure 1). 

Time (min)

Heart Rate (beats/min)

0

20

40

60

80

100

120

140

160

180

200

0 60 120 180 240 300 360 420 480 540 600 660 720

Raw data

15-point moving average

Figure 1. An example of a 12-hour heart rate profile collected from one of the DST during the 

submarine deployment. The dashed line indicates the smoothed heart rate data following an 

unweighted 15-point moving average. Time periods where the 15-point moving average attained 

100 beats/min or greater were considered periods of exercise. For this individual the duration 

and mean intensity of exercise during this 12-hour period was 59 minutes and 131 beats/min, 

respectively. 
9 

Mood States

Mood throughout the study was measured with the Profile of Mood States (POMS) questionnaire 

shown in Appendix C. Subjects scored their response to 13 questions using a visual analogue 

scale. Subjects were administered the test once per week over the entire study period. 

Physical Health Symptoms

During the study all groups completed weekly health-symptoms questionnaires (see 

Appendix D). This questionnaire was developed by WRAIR for studying American troops 

deployed in Bosnia. Symptoms were not broken down by severity for analysis. 

Sleep-Wake Cycle

Techniques used to document sleep habits included a pre-deployment sleep questionnaire (see 

Appendix B), the self-report activity logs (Appendix A) and actigraph monitoring. The predeployment sleep questionnaire was constructed by NSMRL using elements from sleep surveys 

previously reported in the scientific literature (Buysse et al., 1989; Kelly et al., 1996). The selfreport activity log was designed by NSMRL specifically for the current study. Details of the 

administration of the self-reported activity logs are provided above in the section on activity 

levels. Actigraphs are wrist-worn, noninvasive, matchbox-sized devices that record the 

frequency of movement in three planes of motion. Subjects were instructed to wear the 

actigraphs continuously, including during sleep, but excluding water exposure. Actigraphs were 

downloaded approximately every 10 days and were immediately reissued. The longest period of 

sleep taken during a 24-hr period, total sleep amount in a 24-hour cycle, the number of 

awakenings and the total wake time was calculated for each subject. Data were collected, stored 

and analyzed by Walter Reed Army Institute of Research (WRAIR) Department of Operational 

Stress Research. Their full report is provided in Appendix E. 

Caloric Intake

Caloric intake data was gathered from daily self-report dietary logs and weight was measured 

pre-deployment and post-deployment. Self-report dietary logs were recorded during six days 

prior to deployment, three days during the first half of deployment and three days during the last 

half of deployment. Subjects were instructed to record their entire intake except for water. They 

were given examples of portion sizes to assist in recording their intake. All subjects while 

onboard the submarine ate meals provided by the submarine mess. Data from the logs were 

entered into Nutritionist Fiveô software, First DataBank, San Bruno, CA, and analyzed for total 

calories, protein, carbohydrates and fat. 

Ambient berthing noise

Ambient noise in DSTís and SCGís berthing areas was measured using a Questô sound level 

meter, Oconomowoc, WI. Sound pressure level sampling was done 5 feet from the deck in the 

center of the berthing space in 48-hour intervals with two measurements 12 hours apart during 

deployment. Decibels were recorded using an A-weighting and a linear scale. No sound 

measurements were performed for the NDST. 

Submarine atmosphere

Submarine atmosphere was recorded every hour during deployment from the Central 

Atmosphere Monitoring System (CAMS). Measurements were taken in three areas of the 

submarine: submariner berthing, Seal Team berthing and the Fan Room. Average partial 

pressures of oxygen, carbon dioxide, and carbon monoxide were calculated for each day for each 

location based on the submarine barometric pressure. When the CAMS was non-operational 
10 

oxygen and carbon dioxide levels were measured with a portable O2/CO2 gas analyzer. Gas 

measurements were not taken when the submarine ventilated with the outside or when the 

hatches were open while in port. 

Data Analyses

For each individual differences in performance between pre and post-deployment tests were 

calculated as a percent change from their pre-deployment test. These percent changes were then 

used to calculate the mean percentage change and ± 95% confidence limits for each Group. 

Planned comparisons between groups were conducted using independent t-tests, while paired ttests were used to compare pre-deployment and post-deployment changes in the dependent 

variables. Test-retest performance on the Cooper test was assessed using a paired t-test and the 

Pearson Product moment correlation using data from 18 subjects. Sleep, exercise, dietary, and 

mood data were analyzed using repeated measures analysis of variance. Pre-deployment 

frequency of reported subjective ailments were compared to deployment frequency using Chisquare. Statistical significance was set for all tests at p≤0.05. 

RESULTS 

A total of 31 subjects participated, 10 members in the deployed Seal Team (DST), 9 members in 

the non-deployed Seal team (NDST), and 12 members in the submariner control group (SCG). 

The average ages (± SD) of the DST, NDST and SCG were 29 (± 4), 30 (± 6), 28 (± 8) years, 

respectively. Average active duty time in the Navy for DST, NDST and SCG were 8 (± 2) years, 

8 (± 2) years, and 8 (± 4) years, respectively. Prior to this deployment, the DST and NDST were 

transported on a submarine an average of 10 (± 4) and 5 (± 3) times in their careers, respectively. 

For each transport, the DST and NDST spent on average 16 (± 10) and 18 (± 20) days on 

submarine deployment, respectively. The SCG had an average 5 (± 4) years of submarine service 

with 13 (± 14) transports for an average of 19 (± 20) days spent on each deployment. 

Cooper Test

We found a significant practice effect with a 2% mean increase in distance achieved between the 

first and second trial pre-deployment (p<0.05) with no significant change in any of the HR 

variables. The test-retest correlation coefficient for the distance ran was r=0.79 (p<0.001). 

Individual changes in running performance between the second pre-deployment Cooper test and 

the post-deployment Cooper test are shown in figure 2. In the NDST there were approximately 

an equal number of subjects who increased their performance as decreased their performance 

post-deployment. In contrast all but 2 individuals ran a shorter distance post-deployment than 

pre-deployment in the DST. All but two members of the SCG showed increased their distance 

run post-deployment with one individual increasing his distance by almost 1 km. This latter 

submariner also increased his HRmax by 12 beats/min and his HRmean by 4 beats/min during the 

post-deployment test. Interestingly, the two individuals in the SCG that showed a decrease in 

distance run post-deployment were the fastest runners in the SCG. 

A typical heart rate profile over the 12-min run and during recovery is shown in figure 3. 

Maximal heart rate was usually attained during the final minute of exercise and reached over 

90% of the theoretical age predicted maximum heart rate (i.e. predicted maximum HR = 220 - 

age) for all subjects during the pre and post-deployment tests. Furthermore, for the SEALs the 

group average HRmean maintained over the 12-min run was 90% of the predicted maximum heart 

rate on each of the three Cooper tests. For the SGC the average HRmean was 92% of the predicted 
11 

maximum HR during both the pre and post-deployment tests. Table 1 summarizes the 

comparison between the second pre-deployment test and the post-deployment test for the 

measured heart rate variables for each group. For the NDST, none of the variables showed 

significant changes between pre and post-deployment testing. However, the likelihood of 

showing significant differences in the pre versus post-deployment HR variables for the NDST 

was reduced due to the small n. The only variable to show a significant difference between the 

Table 1

Summary of results comparing heart rate measures on the Cooper test pre1

 and postdeployment. Data are means ± SD. 

 

Predeployment Postdeployment n % Change -95% 

Confidence 

limit 

+95% 

Confidence 

limit 

 

HRmean (beats min-1) 

 Submariners 175 ± 10.1 175 ± 9.3 12 +0.1% -3.2% +3.4% 

 DST 174 ± 6.1 175 ± 9.6 10 +0.6% -2.0% +3.2% 

 NDST 164 ± 5.6 166 ± 7.8 6 +1.5% -0.6% +3.6% 

D/ HRmean (m/beat min-1) 

 Submariners 13.1 ± 1.57 14.4 ± 1.75 12 +10.1%* +0.7% +19.4% 

 DST 16.3 ± 1.19 15.2 ± 1.39 10 -7.3%** -10.9% -3.8% 

 NDST 16.5 ± 1.35 17.0 ± 1.28 6 +3.2% -2.9% +9.3% 

HRmax (beats min-1) 

 Submariners 189 ± 10.4 192 ± 9.6 12 +2.0% -1.3% +5.3% 

 DST 185 ± 5.7 185 ± 10.5 10 +0.3% -2.3% +3.0% 

 NDST 176 ± 7.2 179 ± 7.6 6 +1.3% -1.9% +4.4% 

HRrectime (s) 

 Submariners No data No data No data No data No data 

 DST 92 ± 21 136 ± 64 10 +46.8%* +7.8% +85.9% 

 NDST 110 ± 31 140 ± 48 5 +31.5% -30.2% +93.1% 

HRrecslope (beats min-2) 

 Submariners No data No data No data No data No data 

 DST -0.748 ± 0.226 -0.605 ± 0.192 10 -17.1%* -31.3% +3.0% 

 NDST -0.566 ± 0.179 -0.497 ± 0.157 5 -6.9% -42.7% +28.8% 

Notes: 

1

 Data are from the second pre-deployment test for the DST and NDST. 

Significant differences between pre and post deployment tests illustrated by * = (p<0.05), ** = 

(p<0.01) 

HRmean = Mean exercise heart rate. 

HRmax = Maximum exercise heart rate. 

HRrectime = Time taken for the heart rate to drop by 30% from that recorded during the final 5 s of 

exercise.

HRrecslope = Slope of the heart rate response during the first 30 s of recovery. 

n = number of subjects used in the dependent t-test analysis. 

DST = Deployed SEAL team 

NDST = Non deployed SEAL team
12 

Deployed SEALs

Distance run in 12 min (m)

1700

1900

2100

2300

2500

2700

2900

3100

3300

Pre-deployment Post-deployment

Control SEALs

Distance run in 12 min (m)

1700

1900

2100

2300

2500

2700

2900

3100

3300

Pre-deployment Post-deployment

Submariners

Distance run in 12 min (m)

1700

1900

2100

2300

2500

2700

2900

3100

3300

Pre-deployment Post-deployment

Figure 2. Case profiles showing changes in Cooper test performance between the second predeployment test and the post-deployment test for each group.
13 

Time (min)

Heart Rate (beats min-1)

80

100

120

140

160

180

200

220

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Start Exercise

Stop Exercise

HRmax = 194 beats min-1

HRrectime HRmean = 182 beats min = 75 s -1

Figure 3. A typical heart rate profile recorded during the post-deployment Cooper test. The 

theoretical age predicted maximal heart rate (i.e. predicted maximal HR = 220 - age) for this 

subject was 191 beats/min. 

non-deployed and deployed SEALs was the pre-deployment HRmean, which was 9 beats min-1

lower for the NDST (p<0.05). 

Group statistics showed no significant difference between the DST and NDST before 

deployment. However, the DST ran significantly farther than the SCG before deployment 

(p<0.0004, see Table 2). When running performance was expressed as a percentage change in 

the distance run between the pre and post-deployment tests there was a significant difference 

between the SEAL groups (p<0.01). The NDST showed a non-significant 2% (SD ± 6.2%) 

increase in running distance whereas the DST showed a 7% (SD ± 5.1%) decrement in the 

distance ran following deployment (p<0.01). The decrement in performance of the DST was not 

associated with any changes in HRmean or HRmax. HRrectime was between 8% and 86% longer (±

95% confidence limits) following the deployment (p<0.05). In addition, HRrecslope decreased by 

17% (p<0.05) and the D/HRmean ratio decreased by between 4% and 11% (± 95% confidence 

limits, p<0.01) for the DST following deployment (see Table 1). The SCG showed between a 0% 

and 20% (± 95% confidence limits) significant increase in D/HRmean ratio post-deployment 

compared to pre-deployment (p<0.03). Although the DST ran on average 5% further than the 

SCG after deployment, this difference was not significant (p<0.28). 
14 

Shooting

The average number of practice trials (± SD) completed by the SEALs pre-deployment was 4.3 ±

1.19 and was similar for both SEAL teams. Due to scheduling conflicts only one shooting 

sequence was completed pre-deployment by the SCG. When the second and third predeployment trials were compared there was no difference in the number of hits scored (p=0.411), 

however, the test-retest correlation was non-significant (r= 0.015, n=18, p=0.953). Despite poor 

pre-deployment test-retest reliability shooting performance pre-deployment did show a weak 

correlation with post-deployment performance (r=0.494, n=31, p<0.01). This significant 

relationship was largely a result of the SEALs performance since the SCG showed no significant 

relationship between pre and post-deployment shooting scores (r=-0.077, n=12, p=0.812). The 

DST scored significantly more hits than the NDST prior to deployment (29.5 vs. 22.1, 

respectively, p<0.01). There was no effect of deployment on the mean number of hits for any 

group (see Table 2). 

Hand-Grip Strength

We found no significant practice effect for this test. The test-retest correlations were r=0.572 

(right hand, p<0.05) and r=0.565 (left hand, p<0.05). We found the right-hand performance 

correlated with left-hand performance (r=0.653, p<0.05). There was no statistical difference 

among the three groups before deployment. Maximum grip strength pre-deployment was 

statistically unchanged compared to post-deployment for all three groups, with the exception of 

an increase in the left hand of the SCG (p<0.006) (see Table 2). 

Hand-Grip Endurance

We found no significant practice effect for this test. The test-retest correlations were r=0.510 

(right hand, p<0.05) and r=0.520 (left hand, p<0.05). We found the right-hand performance 

correlated with left-hand performance (r=0.700, p<0.05). There was no statistical difference 

among the three groups before deployment. Hand-grip endurance pre-deployment was 

statistically unchanged compared to post-deployment for all three groups, with the exception of a 

decrease in the left hand of the SCG (p<0.042) (see Table 2). 

Manual Dexterity (Gun Assembly)

We found a significant practice effect for this test with an 11% mean decrease in time to finish 

between the first and second trial pre-deployment (p<0.02). The test-retest correlation was 

r=0.620 (p<0.05). There was no was no statistical difference among the three groups before 

deployment. Manual dexterity pre-deployment was statistically unchanged compared to postdeployment for DST and NDST. There was a significant post-deployment decrement for the 

SCG (p<0.015) (see Table 2).
15 

Table 2 

Summary statistics for the performance of each subject group before and after deployment on the 

different tests in the Physical Test battery. Significant differences between pre and post-deployment 

performance are indicated by the * symbol. 

Test Pre-deployment 

Mean (SD) 

Post-deployment

Mean (SD) 

 % Change -95% 

Confidence 

limit 

+95% 

Confidence 

limit 

Cooperís Test Distance in meters 

Submariners 2317 (344) 2520 (279) +10.1%* p<0.002 +0.3% +20.0% 

DST 2839 (192) 2646 (242) -6.8%* p<0.03 -10.5% -3.2% 

NDST 2667 (187) 2730 (262) +2.4% -2.4% +7.1% 

Shooting Number of hits 

 Submariners 18.5 (4.8) 20.4 (3.6) +18.2% -6.3% +42.7% 

 DST 29.5 (4.6) 26.4 (5.0) -9.4% -22.3% +3.6% 

 NDST 22.1 (6.7) 22.2 (8.1) +5.4% -21.8% +32.7% 

Right Hand Grip 

Strength 

Pounds 

 Submariners 128.2 (18.4) 138.8 (21.6) +9.4% -0.9% +19.6% 

 DST 127.7 (12.0) 127.1 (15.3) -0.3% -6.4% +5.7% 

 NDST 129.0 (19.3) 123.9 (15.6) -2.9% -12.6% +6.8% 

Left Hand Grip 

Strength 

Pounds 

 Submariners 122.6 (22.9) 132.8 (24.4) +8.7%* p<0.006 +3.3% +14.1% 

 DST 129.7 (12.0) 124.1 (16.9) -4.3% -11.0% +2.4% 

 NDST 118.8 (15.9) 121.6 (20.8) +2.9% -8.4% +14.1% 

Endurance Right 

Hand Grip 

Seconds 

 Submariners 72.4 (22.7) 70.8 (19.1) +7.9% -25.6% +41.4% 

 DST 66.9 (21.3) 61.8 (19.3) -1.9% -28.4% +24.6% 

 NDST 72.8 (22.4) 69.7 (21.7) -2.5% -19.6% +14.6% 

Endurance Left Hand 

Grip 

Seconds 

 Submariners 67.8 (18.7) 54.8 (14.1) -15.7%* p<0.042 -31.9% +0.5% 

 DST 63.3 (19.0) 65.2 (21.7) +10.3% -25.3% +45.8% 

 NDST 75.9 (21.1) 72.7 (15.7) -0.7% -18.1% +16.8% 

Manual Dexterity1 Seconds 

 Submariners 109.2 (30.6) 152.6 (69.9) +38.1%* p<0.015 +9.4% +66.9% 

 DST 89.8 (16.4) 104.4 (28.4) +17.4% -3.8% +38.7% 

 NDST 114.5 (41.1) 105.7 (31.9) -3.9% -22.7% +14.9% 

Step Test Steps/minute 

 Submariners 55.6 (6.5) 60.7 (7.4) +9.2%* p<0.005 +3.0% +15.9% 

 DST 71.5 (7.3) 64.9 (8.4) -9.2%* p<0.006 -14.9% -3.5% 

 NDST 66.8 (4.7) 67.0 (6.5) +0.3% -5.8% +6.7% 

Pull-ups Counts 

 Submariners 8.1 (4.6) 8.2 (4.3) +7.5% -12.1% +27.1% 

 DST 17.3 (3.4) 17.0 (4.6) -0.3% -20.4% +19.9% 

 NDST 17.9 (5.2) 19.0 (4.4) +8.4% -1.9% +18.7% 

1

Note: An increase in time or positive change on this test is indicative of poorer performance.
16 

Step Test

We found a significant practice effect for this test with a 12% mean increase in the number of 

steps between the first and second trial prior to deployment (p<0.0001). The test-retest 

correlation was r=0.835 (p<0.05). Individual changes in Step test performance between the 

second pre-deployment test and the post-deployment test are shown for each group in figure 4. 

In the NDST there were four individuals who increased performance, three who decreased their 

performance, and two who showed no change following the deployment period. In the DST all 

but one individual showed a decrease in their performance after the deployment. In contrast all 

but 2 submariners improved their performance on the post-deployment test. Group statistics 

showed no significant difference between the DST and NDST before deployment. However, the 

DST and NDST combined achieved significantly more steps than the SCG before deployment 

(69 steps/min vs. 55 steps/min, respectively, p<0.0001). Mean number of steps/min predeployment was statistically unchanged compared to post-deployment for the NDST. For the 

DST the mean number of steps/min post-deployment decreased compared to pre-deployment 

(p<0.006) but increased for the SCG (p<0.005). After deployment there was no longer a 

statistically significant difference in performance between DST and SCG (see Table 2). 

Pull-ups

We found no significant practice effect for this test. The test-retest correlation was r=0.96 

(p<0.05). There was no statistical difference between the DST and NDST before deployment. 

However, the DST and NDST combined achieved more pull-ups than the SCG before 

deployment (18 vs. 8, respectively, p<0.00001), this difference was unchanged after deployment. 

The number of pull-ups post-deployment was statistically unchanged compared to predeployment for all three groups (see Table 2). 

Cognitive Tests

We found no significant changes in any of the three groups between pre-deployment and postdeployment measures of time-to-completion or number of errors for matching-to-sample, 

complex reaction time, visual vigilance, logical reasoning, or repeated acquisition. We did find a 

significant slowing in post-deployment mean response time for serial addition-subtraction 

compared to pre-deployment. This slowing was seen for all three groups, SCG (2232 vs. 2040 

msec, respectively, p<0.004), DST (2049 vs. 1807 msec, respectively, p<0.04) and NDST (2170 

vs. 1897 msec, respectively, p<0.06). There was no change in errors for serial additionsubtraction for any of the three groups over the same testing period.
17 

Deployed SEALs

Number of steps in 1 min

40

45

50

55

60

65

70

75

80

85

90

Pre-deployment Post-deployment

Control SEALs

Number of steps in 1 min

40

45

50

55

60

65

70

75

80

85

90

Pre-deployment Post-deployment

Submariners

Number of steps in 1 min

40

45

50

55

60

65

70

75

80

85

90

Pre-deployment Post-deployment

Figure 4. Case profiles showing changes in the Step test performance between the second predeployment test and the post-deployment test for each group. 
18

Activity Levels

For the NDST, there were no changes in time spent eating, working or recreating over the study 

period. Over the early deployment period the DST spent significantly more time eating and 

recreating and less time working than the SCG (p<0.001). For this same time period the DST had 

66% more free time (recreational time) than the NDST (p<0.001). During the late deployment 

period there was no difference in hours spent eating and working between DST, CSG, and 

NDST. Over the study period no group significantly changed their amount of time spent 

exercising. However the DST spent significantly less time exercising than the NDST over the 

entire study period, 0.7 vs. 2.5 hours/day, respectively (p<0.01). The SCG spent on average 1.5 

hours exercising/day over the study period. There was no statistically significant difference 

between the DST and the SCG in time spent exercising (p<0.07). 

Analysis of the heart rate data showed similar results to that described above for the activity logs. 

For the NDST the total duration of exercise (see Methods section for definition of exercise 

duration based upon HR data) was similar across the study period. During the pre-deployment 

period the NDST spent 9.7% (± 7.8% (SD)) of their total monitored time exercising compared 

with 9.4% (± 7.6%) during the deployment period (p=0.924). In contrast the DST spent 11.0% 

(± 13.4%) of their total monitoring time exercising during the pre-deployment period and only 

5.2%(± 3.1%) during the deployment period (p=0.275). Based upon the HR data there were no 

statistically significant differences in the amount of time spent exercising among the three groups 

during the deployment period or between the NDST and DST during the pre-deployment period. 

For the NDST and the DST the intensity of exercise tended to be slightly greater during the 

deployment period (NDST = 126 ± 15 beats/min (mean ± SD); DST 126 ± 6 beats/min) than 

during the pre-deployment period (NDST = 115 ± 12 beats/min (mean ± SD); DST 113 ± 8 

beats/min). Although the intensity of exercise during deployment was significantly greater than 

that during pre-deployment in the DST (p<0.05), there was no significant difference in exercise 

intensity between the pre-deployment and deployment periods in the NDST (p=0.330). This lack 

of significance was largely due to the high variability in exercise intensity among the NDST. 

During deployment the mean exercise intensity for the SCG was 111 ± 6 beats/min which was 

significantly lower than that recorded for the NDST (p<0.01) and the DST (p<0.0001). 

Mood

There were no significant changes in any of the 13 parameters of mood measurement for the 

NDST over the study. However for the DST, there were significant increases in feelings of 

annoyance, frustration, discouragement, depression, irritability, and tiredness (p<0.05). They also 

had a significant decrease in contentment, energy and activity levels (p<0.05). There were no 

changes in feelings of comfort, stress, nervousness, or tension. The SCG had no change in any of 

the above parameters except for an increase energy during early deployment relative to all other 

periods (p<0.05) and a decrease in activity over the deployment (p<0.003). There were no 

differences in mood parameters between DST and NDST pre-deployment. However, the DSTís 

mood in every category other than discomfort and nervousness was significantly worse than 

NDST during and after the deployment period (p<0.05). 

Health

There were no changes in any of the 21 health symptoms reported by the SCG during patrol 

compared to prepatrol. For the NDST there was a decrease in muscle aches and rashes during the 
19

patrol period compared to prepatrol (both, p<0.04). During patrol, the DST had increases in the 

frequency of sinus troubles (p<0.03), headaches (p<0.04), backaches (p<0.06), constipation 

(p<0.04), and cuts/sores (p<0.03) compared to prepatrol. Whereas, the DST had lower 

complaints of muscle aches (p<0.04) during patrol compared to prepatrol (see Table 3). For the 

DST, the frequency of the following symptoms did not change during deployment compared to 

pre-deployment: flu, head cold, sore throat, difficulty swallowing, allergies, stomach/intestinal 

upset, skin rash, eye/ear/nose problem, chills/fever, hoarseness, heart problems, weight loss/gain, 

dizziness or injury. 

Table 3 

Symptoms with significant cumulative frequency changes 

Control SEALs Prepatrol Patrol p value 

 Muscle aches 47% 20% 0.038 

 Rash 24% 5% 0.037 

Deployed SEALs 

 Sinus problems 20% 48% 0.032 

 Headaches 35% 63% 0.038 

 Backaches 25% 50% 0.058 

 Constipation 0% 19% 0.038 

 Cuts/sores 0% 21% 0.0271 

 Muscle aches 40% 17% 0.039 

Sleep

Sleep data from the activity logs for longest sleeping session and total sleep for each group 

broken down by prepatrol, early patrol (transit time) and late patrol (operations) are tabulated in 

Table 4. Both the SCG and the NDST had no change in their longest sleep session or total hours 

slept during a twenty-four hour period over the entire study. However, the DST had a 29% mean 

increase in their total sleep time from prepatrol to early patrol (7.7 vs. 9.9 hours, respectively, 

p<0.03). Their total sleep time prepatrol was significantly longer than either SCG or NDST 

(p<0.05). During active operations (late patrol), the DST had a decrease in their longest sleep 

session compared to early patrol and prepatrol (5.2 vs. 6.7 and 6.6 hours, respectively, p<0.03). 

The decrease in longest sleep session was also less than either SCG or NDST for the late patrol 

period (p<0.02). 

Walter Reed Army Institute of Research report in Appendix E provides a full description of the 

sleep patterns derived from the actigraph data. Although data artifact arising from an unknown 

source while aboard the submarine made analysis of the sleep patterns for the SCG and DST 

difficult there was sufficient data to make some comparisons between the actigraphs and sleep 

logs over the entire study. On average, for the longest sleep session, subjects reported 0.7 hours 

(42 minutes) more sleep on the sleep logs than were recorded on the actigraph, 6.9 vs. 6.2 

hours/day, respectively (p<0.01). It should be noted that the smallest resolution of the sleep log 

was 0.5 hours (30 minutes) compared to the resolution of 0.017 hours (1 minute) for the 

actigraph data. 
20

Table 4 

The Amount of Sleep Logged for a 24 hour Period 

Control 

SEALs 

Prepatrol Early Patrol Late Patrol Significance 

Longest Sleep 7.4 (0.6) 6.9 (1.1) 7.3 (0.8) No difference 

Total Sleep 8.1 (0.8) 7.3 (1.1) 8.4 (1.3) No difference 

 

Deployed 

SEALs 

 

Longest Sleep 6.6 (0.9) 6.7 (1.7) 5.2 (1.4) Early vs Late 

p=0.026; Pre vs 

Late p=0.013 

Total Sleep 7.7 (1.2) 9.9 (2.4) 8.1 (2.5) Pre vs Early 

p=0.021 

 

Submariners 

Longest Sleep 6.8 (2.6) 6.7 (1.7) 7.0 (1.5) No difference 

Total Sleep 7.6 (2.4) 8.7 (2.6) 8.1 (1.6) No difference 

Notes: Values are means (SD)

Caloric Intake

A summary of the dietary analysis performed on each experimental group is shown in Table 5. 

There were no differences in total daily caloric intake or the amount of protein, carbohydrate or 

fats consumed between any of the groups pre-deployment or in the amount of protein and 

carbohydrates eaten during the deployment. During early deployment the SCG and DST 

consumed a greater amount of fat than the NDST (SCG vs. NDST, p<0.001; DST vs. NDST, 

p<0.05). During the late deployment period the NDST had similar total daily caloric intake and 

protein, carbohydrate and fat consumption as the SCG and DST. However, during this same time 

period, the DST reported a lower total daily caloric intake than the SCG (p<0.05) which was 

predominantly a result of a lower amount of fat consumed by the DST compared to the SCG 

(p<0.05). 

A comparison of the dietary logs within groups revealed that the SCG did not change their total 

daily caloric intake or the amount of protein, carbohydrate or fats eaten during the entire study 

period. In contrast, the DST had a significant reduction in their carbohydrate intake during early 

and late deployment relative to pre-deployment (both p<0.05). However, this reduction in 

carbohydrate consumed during deployment did not result in a significant change in the total daily 

caloric intake over the study period (F2,74 = 2.8, p=0.064). The NDST reported a significant 

reduction in their daily caloric intake during the early (p<0.01) and late deployment time period 

(p<0.05) compared to pre-deployment. The reduction in caloric intake by the NDST during the 

deployment phase was a result of a lower consumption of protein and carbohydrates during both 

early and late deployment compared to pre-deployment (all comparisons p<0.05). There were no 
21

significant differences in weight between DST and NDST. Differences in body weight between 

DST and SCG did not reach statistical significance (84 kg vs 91 kg, respectively, p=0.08). 

Ambient Noise

A-weighted noise measurements of the DSTís berthing area were significantly higher than the 

SCGís berthing area over the deployment, 57 vs. 43 dB, respectively (p<0.000001). This 

difference resulted in a berthing area for the DST that was louder than SCGís berthing area for 

noise weighted in the human hearing range. Comparison of the berthing areas was not 

significantly different for noise measured on a linear scale 80 vs. 79 dB, respectively. 

Submarine Atmosphere

There was a total of 26 days of atmosphere data collected over the 33 days of SEAL Team 

deployment. Carbon monoxide levels never exceeded the limit of 15 ppm in any of the three 

locations over the deployment. The mean carbon monoxide level over the deployment was 1.65 

ppm. Daily mean oxygen levels exceeded the upper limit of 160 mmHg for 3 of the 26 days 

(12%). There was no day in which the mean oxygen level fell below the 130-mmHg limit. The 

average oxygen level over the deployment was 145 mmHg (see figure 5). Daily mean carbon 

dioxide levels exceeded the limit of 3.8 mmHg for 9 of the 26 days (35%). The average carbon 

dioxide level over deployment was 3.5 mmHg (see figure 6). 
22

Table 5 

Dietary analysis showing the average daily caloric intake (KCal) and average amount of 

protein, carbohydrates and fat (in grams) consumed per day during the study period by 

each experimental group. 

 Mean SD SEM Range 

Pre-deployment 

Control SEALs KCAL 2836 1182 203 5551 

 PROTEIN 124 58 10 238 

 CARB 335 128 22 670 

 FAT 94 62 11 301 

Deployed SEALs KCAL 2464 1370 250 6710 

 PROTEIN 100 42 8 154 

 CARB 285 147 27 628 

 FAT 85 57 10 215 

Submariners KCAL 2767 1235 178 5407 

 PROTEIN 109 42 6 188 

 CARB 352 207 30 1010 

 FAT 97 45 7 194 

Early Deployment 

Control SEALs KCAL 2054 522 114 2180 

 PROTEIN 100 44 10 181 

 CARB 258 86 19 378 

 FAT 62 32 7 99 

Deployed SEALs KCAL 2038 636 122 2705 

 PROTEIN 107 34 7 128 

 CARB 201 103 20 386 

 FAT 93 31 6 127 

Submariners KCAL 2423 1019 170 4477 

 PROTEIN 107 46 8 211 

 CARB 277 154 26 774 

 FAT 102 43 7 178 

Late Deployment 

Control SEALs KCAL 2176 626 128 2553 

 PROTEIN 89 24 5 86 

 CARB 261 99 20 399 

 FAT 81 49 10 202 

Deployed SEALs KCAL 1813 613 137 2157 

 PROTEIN 106 49 11 168 

 CARB 204 79 18 332 

 FAT 61 25 6 83 

Submariners KCAL 2458 1092 182 4579 

 PROTEIN 105 43 7 166 

 CARB 271 134 22 538 

 FAT 99 47 8 222 
23

Figure 5. Daily mean oxygen levels in the fan room 

Figure 6. Daily mean carbon dioxide levels in the fan room 

Daily Mean Oxygen Levels in fan room 

 Days

O2 in mmHg

124

126

128

130

132

134

136

138

140

142

144

146

148

150

152

154

156

158

160

162

164

166

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

 Daily Mean Carbon Dioxide Levels in Fan Room 

 Days

CO2 in mmHg

0

1

2

3

4

5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
24

DISCUSSION 

The results of the current study indicate that SEALs experience a significant decrease in aerobic 

and anaerobic performance following a 33-day submarine deployment. The decrease in aerobic 

performance was not associated with changes in exercise heart rate since HRmean and HRmax were 

similar during the pre and post-deployment Cooper tests. However, it is well known that changes 

in running performance after training or detraining greatly exceed any associated changes in the 

cardiovascular system involving oxygen consumption or heart rate (Lambert et al., 1998). 

Consequently, the distance run on the Cooper test will give a better indication of an individualís 

state of aerobic conditioning than measures of exercise heart rate. Furthermore, from a practical 

perspective running performance is more directly related to the physical demands of actual 

mission performance than physiological measures of cardiovascular function. 

However, misleading or inappropriate conclusions could occur if running performance is used as 

the sole criterion for determining the state of aerobic conditioning in individuals whose 

motivation to perform maximally may differ between testing conditions. Even though the SEALs 

are known to be highly competitive and motivated individuals (Braun, 1994) the fact that they 

knew the objectives of the study, could have influenced them to under perform following 

deployment to magnify deconditioning effects. This strategy is motivated by the fact that large 

decrements in aerobic performance following the submarine deployment might prompt SEAL 

commanders to find alternative methods to deploy their troops for future missions. From the 

deployed SEALs perspective this would mean less time away from home and family, as well as 

less time within the cramped confinements of the submarine. Our data on mood changes verify 

the hypothesis that SEALs do not ìenjoyî their deployment time. In fact, 9 of the 13 mood 

parameters indicated increases in negative emotions during the deployment. In contrast, 

submariners had no change in 11 of 13 mood parameters. Despite this knowledge, the similar pre 

and post-deployment exercise HR data suggest that the subjects were equally motivated during 

the pre and post-deployment Cooper tests. Since running speed (and hence distance achieved in a 

given time) is linearly related to exercise HR (Lambert et al., 1998) one would expect the 

D/HRmean ratio to be unchanged if motivation factors were the only variable to influence running 

speed between different testing conditions. However, the deployed SEALs showed a significant 

decrease in the D/HRmean ratio post-deployment. Since a decrease in D/HRmean indicates that 

running performance is less efficient, the results suggest either a real deconditioning effect or 

significant differences in the environmental testing conditions between the pre and postdeployment tests. Since the pre and post-deployment tests were conducted at the same time of 

day under similar weather conditions, the decrease in running performance is most likely a result 

of aerobic deconditioning. 

Further evidence of aerobic deconditioning in the deployed SEALs is reflected by the changes in 

the recovery heart rate profiles following the Cooper test. Heart rate recovery is correspondingly 

faster in those individuals who have a higher aerobic capacity (Cardus and Spencer, 1976; 

Hagberg et al., 1980; Kirby and Hartung, 1980; Darr et al., 1988). Furthermore, endurance 

training results in a more rapid rate of recovery in HR following exercise (Hagberg et al., 1980). 

Consequently, in the present study, slower rates of heart rate recovery following exertion were 

attributed to a deconditioning effect. We provide two indices of HR recovery that may be useful 
25

to follow changes in the aerobic training status of an individual. The first index, HRrectime, 

provides a quick field-based estimate of aerobic training status that requires few calculations or 

knowledge about the characteristics of the HR recovery profile. This index includes both the 

initial fast component and a portion of the subsequent slow component of the exponential decline 

in HR following exercise (Imai et al., 1994). Because the time constant of the slow component of 

the HR recovery curve depends on the exercise workload (Imai et al., 1994), HRrectime will be 

somewhat sensitive to differences in the running speed between tests. Results of the present 

study indicate that the deployed SEALs had a substantial increase in recovery time following the 

submarine deployment as measured by the HRrectime index. This finding is tempered somewhat by 

the fact that the control SEALs also showed an increase in HRrectime all be it a non-significant 

one. 

The second index of HR recovery, HRrecslope, focuses on the initial fast component of the HR 

recovery curve which is unaffected by differences in the workload of the preceding exercise 

(Millahn and Helke, 1968; Nandi and Spodick, 1977; Imai et al., 1994). Past research has shown 

that there are marked differences in the fast phase of recovery between aerobically trained and 

untrained individuals (Darr et al., 1988). In the present study, the lack of a significant difference 

in HRrecslope between the DST and NDST post-deployment most likely reflects the large 

variability of this measure within the groups as well as the small sample size of the groups. 

However, results from the more powerful within group analysis show a significant 17% decrease 

in HRrecslope of the deployed SEALs following deployment. Nevertheless, the 95% confidence 

intervals for the change in the HRrecslope are large and show a substantial overlap with the 95% 

confidence intervals for the HRrecslope of the NDST 

Our results on the one-minute step test suggest that DSTís anaerobic condition was also 

adversely affected by the submarine deployment. Previous studies have demonstrated up to 20% 

decrements in the anaerobic threshold of non-exercising submariners after a prolonged 

deployment (Bennett et al., 1985). Despite the DSTís superior performance in both the step-test 

and Cooper test performance pre-deployment compared to the SCG, they were found to perform 

only marginally better (but not statistically significantly better) than the SCG after deployment. 

An aerobic and anaerobic performance of the DST that is statistically no better than the 

submarinerís performance is of considerable concern, given that, other than teamwork, stamina 

was listed as the most important attribute to successful completion of SEAL operations 

(Prusaczyk et al., 1995). 

One of the main reasons for the statistically similar levels of physical fitness between the SCG 

and DST post-deployment was the significant improvement in anaerobic and aerobic 

performance of the SCG. This is in marked contrast to previous studies in which significant 

decrements in physical fitness have been found in submariners following a deployment (Knight 

et al., 1981; Bennett et al., 1985). In the current study, practice effects will likely account for 

some of the SCGís improved performance after deployment since this group only performed the 

physical test battery once prior to deployment. An additional factor that may have contributed to 

the increase in post-deployment performance is subject selection bias. Of note was the fact that 

several of the SCG were close to not meeting the US. Navy physical readiness standards and 

used the study as a means to motivate themselves to improve their fitness. Furthermore, the SCG 

reported exercising on average more than twice as long as the DST during the study period. 
26

However, the variability in the reported daily exercise time of the DST and SCG groups was 

such that this difference was not statistically significant. 

The precise cause of the deployed SEALs deconditioning is less clear. Unlike submarine 

personnel, SEALs do not have to perform any watch standing during their transit time to the 

theater of operations as evidenced by the significant increase in self reported hours spent 

sleeping, eating, and recreating during early deployment. Thus, during this transit period SEALs 

have considerably more free time to exercise compared to when they are ported at their home 

base. This increased time available for physical training may not be utilized due to the limited 

space and availability of exercise equipment on board. The DSTís constellation of increased 

medical symptoms in headache, backache, constipation and sinuses fit the construct of increased 

inactivity or time spent in recumbent positions. Furthermore, decreased motivation and 

disruption from their command physical training regimen might impact a SEALís adherence to a 

regular training program while on submarine operations (Vickers et al., 1982). Despite these 

factors, the deployed SEALís activity logs showed no change in the amount of daily exercise 

performed between the pre-deployment and deployment study period. However, the DST 

consistently spent less time exercising than their non-deployed colleagues did. 

STUDY LIMITATIONS 

A caveat to these data should be made in view of the possibilities that the statistical analyses may 

contain Type I and Type II errors. A Type I error occurs when the true hypothesis of no 

difference between two means is erroneously rejected. Due to the large number of variables 

analyzed in this study it is probable that there are several false positive results. As each 

comparison was an a priori planned comparison, analysis of the data are presented without 

correction for multiple comparisons. The second type of error (Type II error) occurs when we 

falsely accept the hypothesis that there is no difference between two means. This can occur 

when there is an insufficient number of subjects to confidently detect a significant difference 

between two means. Due to the large variability inherent in field based studies it is desirable to 

employ large sample sizes to ensure sufficient statistical power to observe significant differences 

between groups in the variables of interest when they exist. In the present study operational 

requirements and the small subject population pool limited the number of subjects in each group. 

For example, for the DST the entire complement of individuals on the mission volunteered as 

subjects. Consequently, there may be several comparisons where even though large differences 

were shown there was insufficient statistical power to observe a significant difference at the 

p<0.05 level. In view of this fact the reader should keep in mind the 95% confidence limits 

shown for the percent change for the different variables between pre and post-deployment when 

interpreting the statistical findings shown in the results section. 

For some of the performance tests the 95% confidence limits for the percent change in 

performance between the pre and post-deployment test is quite large. The source of this 

variability in the different groups is wide ranging and can include: natural day-to-day variability, 

test-retest reliability of the given test, differences in motivation, as well as individual response 

differences to prolonged confinement aboard the submarine. The results provide an indication of 

systematic bias resulting from practice effects and relative test-retest reliability for the different 
27

tests in the physical performance battery. While some test showed good test-retest reliability (e.g. 

pull-ups) others showed poor reliability. In particular the shooting test showed little consistency 

in relative subject performance for the number of hits on target during repeated testing. In view 

of the poor relative reliability of the shooting test this test may not be reliable enough to detect a 

measurable change in performance as a result of the deployment. However, it should be noted 

that shooting performance was conducted under rested conditions and before completing the 

running test. It is possible that if the shooting test had been performed immediately following 

the Cooper test that the effects of the deployment on shooting performance may have been more 

apparent. Given the fact that the recovery time after aerobic activity is longer following the 

deployment it is possible that shooting performance immediately after extended physical activity 

could be impaired to a greater extent following deployment than before deployment. 

Some of the poor repeatability in test-retest performance may be due to differences in subject 

motivation at the difference test times. Although analysis of the SEALs heart rate data during the 

Cooper tests suggest that individuals were motivated sufficiently enough to approach maximal 

performance during the running test, this may not have been so for other tests. Anecdotal 

observations suggest the strong possibility that certain subjectís motivation were not constant 

over the study period. 

An additional confounding factor that may have potentially impacted post-deployment 

performance of the DST is the five-hour time difference between Korea and Hawaii. Although 

the DST performed the pre and post-deployment tests at the same time of day, their circadian 

rhythms will likely have not been fully synchronized with Hawaii Time during the postdeployment testing. Experimental studies on the effects of circadian rhythms on performance 

have shown that factors such as flexibility, muscle strength and short term high power output 

vary with time of day in a sinusoidal manner and peak in the early evening close to the daily 

maximum in body temperature (Atkinson and Reilly, 1996). Furthermore prolonged 

submaximal exercise carried out in hot conditions shows optimal performance in the morning 

(Atkinson and Reilly, 1996). However, in the present study any jet-lag or circadian asynchrony 

in the DST will likely have had only a small impact on their post-deployment performance tests 

for a number of reasons. Firstly, the DST were not tested until at least 24 hours after arriving in 

Hawaii, thus permitting a certain amount of recovery from the jet-lag before testing. Secondly, 

the considerable interindividual variation in responses to sleep loss (Meney et al., 1998) as well 

as individual differences in performance rhythms (Atkinson and Reilly, 1996) will likely have 

reduced the chances of observing a statistically measurable circadian change in performance 

between the pre and post-deployment tests. The lack of a significant difference in hand grip 

strength between the pre and post-deployment tests provides some evidence to suggest that 

circadian effects if present had minimal impact on the DST post-deployment performance. 

Nevertheless evidence from the scientific literature suggests that small decreases in anaerobic 

capacity and running performance could be expected immediately following an eastward flight 

across six time zones (Wright et al., 1983). 

During field based experiments it is not always possible to perform pre and post-deployment 

tests at the same time of day or at the same time points in the circadian cycle. When this occurs, 

the effects of circadian variation may significantly compound or alleviate any performance 

changes resulting from other mission related environmental stresses. Clearly some means of 
28

accounting for circadian variation on the performance of the physical and cognitive test batteries 

is needed to better isolate the effects of environmental factors on mission related performance. It 

is therefore recommended that the current physical and cognitive SOF mission related test 

batteries undergo a carefully controlled study to detect the influence of circadian variation on the 

various tests. Such a study is needed so that (1) past and future studies may better determine the 

true effects of other environmental stresses on mission related performance and (2) to determine 

the utility of each test from the standpoint of repeatability. 

As the current study was a non-interventional field study conducted during actual training 

operations there were many intervening variables that could potentially impact SEAL 

performance. Attempts were made to monitor those variables that were thought to potentially 

have the largest effect on SEAL performance. Monitoring techniques were used that attempted 

to minimize the impact on the SEALs mission while obtaining the necessary data. However, to 

have minimal impact on the DSTs mission the periods selected for heart rate monitoring may not 

have been representative of the average activity levels over the deployment period (i.e., 

monitoring during particularly quiet or busy periods of time). Several attempts were made to 

monitor activity levels and heart rate during Dry Deck Shelter (DDS) and Seal Delivery Vehicle 

(SDV) operations, however repeated losses and breakageís of our monitoring equipment 

necessitated aborting data collection during these operations. Consequently, activity levels of the 

DST (based on the heart rate data) may have been underestimated during the latter stages of the 

mission when DDS/SDV operations were conducted. 

One unexpected finding was that exercise intensity of the DST derived from the heart rate data 

was significantly greater during deployment than during the pre-deployment period. This 

finding possibly reflects the nature of activities preformed during the week prior to deployment 

when both heart rate and the activity log data were collected. Due to the limited number of days 

of heart rate monitoring during the pre-deployment period it is possible that the combination of 

sampling bias and the changes in the SEALís work schedules (required to prepare for the 

mission) resulted in estimates of exercise intensity that were atypical of their normal working 

week at their home command. 

The large differences in reported daily exercise time between the control SEALs and deployed 

SEALs during the week before deployment may reflect the lack of free time available for the 

deployed SEALs to do additional physical exercise due to the demands of preparing for the 

mission. Indeed the DST reported working longer hours than the NDST during the predeployment period. However, the duration of exercise determined from the pre-deployment 

heart rate data did not confirm differences in exercise time between the two SEAL groups. This 

discrepancy could be due to a number of factors. Firstly, the heart rate data does not distinguish 

between heavy physical work performed during their normal daily routine and formal scheduled 

exercise. In contrast the activity logs separate out the time spent working and the time spent 

exercising. If the DST spent a good portion of their working hours doing heavy manual work 

(i.e., packing equipment for the mission) it will be counted as exercise time if their heart rate was 

maintained above 100 beats/min for 15 min or longer. Therefore even though the DST spent less 

time formally exercising during the pre-deployment period than the NDST, the increase in heavy 

physical activity during the DST working hours may have offset the reduction in formal exercise. 
29

One of the limitations of the activity logs is that they do not show if there were any differences in 

the intensity or type of exercise performed while on land or aboard the submarine. It is possible 

that the DST switched from a predominantly aerobic training program pre-deployment to a 

largely calisthenic and strength training program during the mission and/or that the intensity of 

their aerobic workouts while aboard the submarine were significantly reduced. Even if the 

duration and frequency of exercise is maintained constant, reductions in training intensity can 

lead to a significant loss in aerobic power (Hickson et al., 1985). However, evidence from the 

heart rate data collected during deployment shows that the intensity of exercise was similar in the 

DST and NDST. According to this finding it would seem that the deconditioning of the DST 

does not appear to be a result of a reduction in the intensity of exercise while aboard the 

submarine. 

A more likely explanation for the decrease in running performance of the DST following 

deployment is a reduction in running specific training aboard the submarine. Although there was 

one treadmill aboard the submarine demand for its use may have necessitated that the SEALs 

switch to the other forms of exercise. The other types of exercise equipment available aboard the 

submarine included two rowing machines, one stair climber, two exercise bikes and a set of free 

weights. Due to the specificity of training, even if other non running aerobic activities (e.g. 

bicycling) are substituted for running training current evidence suggests that there is limited 

cross training benefits to be gained (Pierce et al., 1990; Tanaka, 1994). Consequently, a 

prolonged layoff from running specific training could lead to reduced running performance 

despite substituting running training with other forms of aerobic exercise. 

A further study limitation was the fact that post-deployment testing on most of the DST was 

conducted 9 days after they left the submarine (two SEALs remained on the submarine for a 

further 4 days before flying home). During the first 7 days after leaving the submarine the DST 

were in Korea waiting for commercial air transportation to Pearl Harbor, HI. As no monitoring 

of activity was conducted during this period little is known of their activity levels during this 

time. Given the free time and opportunity it is likely that the SEALs continued some sort of 

aerobic training. If activities such as running were engaged in during this free time it is possible 

that some of the decrements in aerobic performance resulting from the submarine deployment 

may have been offset. However, the extent of any activity during this time period and its 

potential effects on post-deployment test performance is unknown. 

One final note that should be considered when interpreting the results of the current study is that 

this research was performed on a single submarine platform using SEALs from one command. 

Personal and group dynamics of other SEAL teams may be different than those of SEAL Team 

One resulting in different approaches to physical training while on prolonged submarine 

missions. Differences in command leadership as well as mission duration, objectives and 

requirements could have significant impact on the degree of deconditioning following a 

prolonged submarine mission. Furthermore, differences in the submarine platform could 

significantly impact the working and living conditions of the SEAL team and lead to different 

outcomes on mission related performance. For example, when compared to a converted ballistic 

missile submarine the fast attack submarine contains significantly less space for berthing and 

exercise equipment. Consequently, prolonged missions aboard a fast attack could potentially 
30

have more of a negative impact on SOF mission related performance than that noted in the 

present study. 

POSSIBLE STRATEGIES FOR MITIGATING DECONDITIONING 

Since any factor that potentially impacts mission success is a major concern for Special 

Operations Forces, countermeasures should be sought to maintain the physical fitness of SEALs 

during extended submarine deployments. Providing exercise equipment and structured training 

programs that permit SEALs to maintain on board exercise regimens of similar type, duration, 

frequency and intensity as land-based regimens may prove fruitful for avoiding aerobic and 

anaerobic deconditioning during prolonged submarine deployments. However, given the limited 

space for exercise equipment on board, especially in fast attack submarines, considerable 

ingenuity will be required in the design and implementation of these training regimens. In view 

of this it would be prudent to explore new recent technologies for maintaining or even improving 

the physical fitness of SEALs while onboard the submarine. One such new technology that 

shows promise for improving aerobic endurance is respiratory muscle training. This training 

requires little equipment, can be performed by multiple people at the same time and can be easily 

conducted in the confined space of a submarine. Current research indicates that submaximum 

endurance capacity can be improved by as much as 50% after 4 weeks of respiratory muscle 

training (Boutellier and Piwko, 1992; Boutellier et al., 1992). As a side benefit those individuals 

who had been shown to retain CO2 during heavy exercise significantly reduced their PETCO2

following respiratory muscle training. This reduction in PETCO2 has important implications for 

SOF diving missions where high CO2 levels have been found to increase the risk of 

decompression illness (Hodes & Larrabee, 1946), oxygen toxicity (Lanphier, 1955, 1963; 

Lanphier & Camporesi, 1993) and the loss of consciousness underwater (Lanphier, 1980, 1988; 

Morrison et al., 1978; Warkander et al., 1990). 

CONCLUSIONS AND RECOMMENDATIONS 

• SEALs on submarine deployment tend to exercise less than their counterparts remaining at 

their home command. 

• The decrease in running performance and the suggestion of slower heart rate recovery 

profiles of US Navy SEALs following a 33-day submarine deployment indicate that 

prolonged confinement aboard a submarine can lead to aerobic deconditioning. 

• Decreases in the SEALs step test performance suggest that activities that require anaerobic 

bursts may also be impaired following a prolonged submarine deployment. 

• Some of the observed decrements in aerobic and anaerobic performance of the DST may 

have been due to the combined effects of jet-lag and circadian asynchrony as a result of 

traveling from Korea to Hawaii immediately before conducting the post-tests. 
31

• For the DST shooting performance, gross manual dexterity, muscular strength and muscular 

endurance and cognitive function were not significantly affected by the 33-day submarine 

deployment. 

• There were significant increases in medical complaints for sinuses, headaches, backaches, 

constipation, and cuts/sores during the deployment for the deployed SOF unit. 

• The submarine deployment has a significant negative affect on the SEALís mood 

• It is unknown to what level the observed degree of deconditioning will impact the SEALs 

performance during an actual mission; however, it can be inferred from the results that 

mission-related performance will be most impacted during and immediately following 

extended periods of high intensity physical exertion. 

• Mission elements that require the SEAL to recover quickly and react following periods of 

heavy exertion may be compromised by the delay in recovery time associated with aerobic 

deconditioning. 

• Recommendations for mitigation of deconditioning effects include: 

• Providing a structured physical training program that can be conducted on board the 

submarine that permit the SEALs to engage in exercises of similar type, duration, 

frequency and intensity as their normal land-based exercise regimens. 

• Minimize the SEALs time aboard the submarine to that necessary to accomplish the 

mission. 

• Explore the use of new training technologies such as respiratory muscle training for 

maintaining or improving aerobic performance while on extended missions. 
32

ACKNOWLEDGMENTS 

Supported by the US Special Operations Command. The views expressed in this report are those 

of the authors and do not reflect the official policy or position of the Department of the Navy, the 

Department of Defense or the US Government. This work was done by US Government 

employees as part of their official duties and therefore cannot be copyrighted. We wish to thank 

CDR Howard F. Reese, Commanding Officer of the USS Kamehameha (SSN 642) and CDR 

Gerald Weer, Commanding Officer of SDV Team One for their cooperation in this study. We 

also wish to thank all the subjects who participated in this study. 

COLLABORATORS/CONTRACTORS 

Naval Submarine Medical Research Laboratory, Groton, CT 

LT D. White, ENS T Tuten, HM2 A. Miller

Walter Reed Army Institute of Research, Forest Glen, MD 

MAJ S. Campbell, CPT M. Kautz, SSG J. Eline, 

Ms H. Sing, Ms A. Welsh, Dr. M. Thomas, CPT D. Ritzer 

 

Naval Medical Research Institute, Bethesda, MD 

Dr. D. Hyde (now stationed at the Uniform Services University of Health Sciences, 

Bethesda, MD), 

Mr. W. Long (now stationed at the Naval Experimental Dive Unit, Panama City, FL) 

Submarine Squadron One, HI 

LCDR P. Willette, HMCS T. Bartholomew (Squadron One Medical)
33

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37

APPENDIX A: SELF-REPORT ACTIVITY LOG 
38

APPENDIX B: SLEEP QUESTIONNAIRE 

NSMRL SLEEP Inventory

(Please print) 

 Name__________________________________________

1) Your age in years ___________ Height (inches) _____________ Weight (pounds) ________ 

2a) Marital status (check one):  single  married  divorced  separated  widowed 

2b) While on shore do you live with any children under age 5?  yes  no 

3) How many years did you complete for each of the following, and did you graduate? 

Number of Years Did You Graduate? 

High School _______________  Yes  No 

Technical School _______________  Yes  No 

College _______________  Yes  No 

4a) What is your rank and rate? ________________________________________________________ 

4b) Briefly list your principle duties _____________________________________________________ 

_____________________________________________________________________________________

__ 

4c) On how many different occasions have you been transported on a submarine ?______________ 

4d) What is the average amount of time (days) you spend on a submarine per operation 

5 How long have you been in the Navy? __________ years, _________ months 

6) Do you consider your work activities to be (please check one): 

 Very hard physical work 

 Heavy physical work 

 An average load of physical work 

 Light physical work 

 Very light physical work 

7a) When at sea on a submarine how many hours (on average out of 24 hours) do you spend 

working ________ training ________ exercising ________ sleeping 

7b) On average, how many hours sleep do you get per 24 hours when 

At Sea ________ On an Operation_____ At Home ________ On 

Leave ________ 

8) How often are you sick enough to see a member of the medical staff? (Check one) 
39

  two or more times a year  about once a year  about once every two years less than every 

two years 

9) Do you have any medical condition that affects your sleep?  yes  no 

10) Do you have another job while on shore for additional income?  yes  no 

11) How often do you use the following when on an operation . . . check one space for each item 

listed below. 

ITEM Every day More than 

once a week 

About once 

 a week 

About once 

 a month 

 Never or 

Almost Never 

Aspirin or equivalent 

Antacids 

Laxatives 

Cough and cold medicines 

Sleeping pills 

Antihistamines (Benadryl) 

Caffeine tables 

Other medicine or drugs 

(please specify below) 

12a) How many cups/cans do you typically drink on operations per 24 hours? Check one space for 

each item listed. 

More than 5 3 to 5 1 or 2 Less than 1 None 

Coffee 

Tea (caffeinated) 

Cola 

(caffeinated) 

12b) How many cups/cans do you typically drink when on-duty ashore? Check one space for each 

item listed. 

More than 5 3 to 5 1 or 2 Less than 1 None 

Coffee 

Tea (caffeinated) 

Cola 

(caffeinated) 
40

12c) How many cups/cans do you typically drink when on liberty? Check one space for each item 

listed. 

More than 5 3 to 5 1 or 2 Less than 1 None 

Coffee 

Tea (caffeinated) 

Cola 

(caffeinated) 

13) Do you smoke tobacco?  yes  no 

If yes, how much do you smoke per day on the average? (Enter number) 

How many cigarettes per day? ______ How many cigars per day? ______ 

Do you use chewing tobacco?  yes  no Dip tobacco?  yes  no 

 How often?__________________________ How often?________________ 

14) When at sea, how physically tired do you usually feel while on the submarine? 

 Not at all  A little  Quite a bit  Extremely 

15) When at sea, how mentally tired do you usually feel while on the submarine ? 

 Not at all  A little  Quite a bit  Extremely 

16) When at sea, how tense do you usually feel while on the submarine? 

 Not at all  A little  Quite a bit  Extremely 

17) How often do you nod off when you should be alert while on the submarine? 

 Never  Rarely (1 or 2 times)  Occasionally (4 or 5 times)  Frequently 

18) Please complete the following statement for days when you are home on several days leave: 

 

 AM AM 

I usually go to sleep at _____ PM (circle one) and get up at ______ PM (circle one). 

 AM 

For additional sleep hours, if any, I usually go to sleep at ______ PM (circle one) 

 AM 

and get up at ______ PM (circle one). 

19) Do you nap even when you do not feel very tired?  yes  no 

20) Some people feel older or younger than the age they are. How old do you feel? ________ 

(years) 

21) You wish to be at your peak performance for an important test which you know is going to be 

mentally exhausting and which lasts for two hours. You are entirely free to plan your day. 

Which one of the following times would you choose to take the test? (Check one box) 
41

 8:00 - 10:00 AM 

 11:00 AM - 1:00 PM 

 3:00 - 5:00 PM 

 7:00 - 9:00 PM 

22) Ideally, how many hours of sleep would you like to get on most days ?____________ 

Key for questions 23 - 36 

Never - once or twice in lifetime Often - once or twice a week 

Rarely - once or twice a year Frequently - three or four times a week 

Sometimes - once or twice a month Always - five times a week or more 

23) How often do you have difficulty falling asleep?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

24) How often after falling asleep, do you waken early and canít get back to sleep again? 

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

25) How often do you have difficulty waking up?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

26) How often do you have difficulty getting out of bed?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always
42

27) How often do you feel overly tired when awake?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

28) How often do you take naps?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

29) How often do you have difficulty staying awake?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

30) How often do you have restless sleep or disturbing dreams or nightmares?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

31) How often after falling asleep do you wake up by yourself and go back to sleep?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always
43

32) Do you usually feel well rested after you wake up and get out of bed?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

33) How often do you suffer from digestive problems such as indigestion, heartburn, 

constipation, diarrhea, and/or cramps?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

 On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

34) How often do you suffer from headache?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

35) Do you feel as though you are getting enough sleep? 

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 

36) How often do you find yourself unable to concentrate on what you are doing?

At Sea on sub Never Rarely Sometimes Often Frequently Always 

On Operations Never Rarely Sometimes Often Frequently Always 

Working Ashore Never Rarely Sometimes Often Frequently Always 

On Leave Never Rarely Sometimes Often Frequently Always 
44

APPENDIX C: PROFILE OF MOOD STATES 

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3- I was active.

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45

APPENDIX D: HEALTH SYMPTOMS QUESTIONNAIRE 

®

Deployment Assessment Medical Questionnaire

NAME

Date Completed

Please indicate if you experienced the

following physical health symptoms

overthe PAST WEEK:

Flu...,

Head Cold

Sinus Trouble

Sore Throat

Difficulty Swallowing

Headache

Back Problems ,

Allergies

Stomach/Intestinal Upset

Muscle Aches or Cramps

Aching Joints and Bones

Constipation.

Skin Rash.

Eye/Ear/Nose Problem

Chills/Fever........ ,

Hoarseness

Heart Problems.

Weight Loss/Gain

Dizziness,...,,...,..,........

Cuts/Sores ..,,.,,.,,,

Injury (Specify)

Other (Specify)

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46

APPENDIX E: WALTER REED ARMY INSTITUTE OF RESEARCH REPORT ON 

SLEEP PATTERNS DURING OPERATION FOAL EAGLE 

U.S. ARMY MEDICAL RESEARCH AND MATERIEL COMMAND 

 

An Objective Evaluation of Quantity and Quality of Sleep 

as Determined by Wrist Actigraphy 

in U.S. Navy Special Warfare Personnel 

during Operation Foal Eagle 

MAJ Spencer J. Campbell, Ph.D. 

CPT Mary A. Kautz, Ph.D. 

Helen C. Sing, M.S.

Maria L. Thomas, Ph.D. 

Amy B. Welsh, B.S. 

SSG John E. Eline 

August 1999

The views expressed in this report are those of the authors and do not necessarily represent official policy or position 

of the Department of Defense, Department of the Army, Army Medical Department, Army Medical Research and 

Materiel Command, Walter Reed Army Medical Center, Walter Reed Army Institute of Research, or the U.S. 

government.

WALTER REED ARMY INSTITUTE of RESEARCH

Division of Neuropsychiatry

Departments of Operational Stress Research,

Neurobiology and Behavior, and Biomedical 

Assessment

Washington, DC 20307-5100

301-319-9645

DSN 319-9645
47

ABSTRACT 

The goal of the study was to determine performance effects of extended exposure to the 

submarine environment on U.S. Navy Special Warfare Personnel (i.e., SEALs) deployed on 

Operation Foal Eagle compared with that of U.S. Navy SEAL and Submariner control groups. 

As a central component of this study, a collaborative effort between the Walter Reed Army 

Institute of Research (WRAIR) and the Naval Submarine Medical Research Laboratory was 

established to field Actigraphs to assess sleep quantity and quality. The WRAIR Actigraph is a 

wrist-worn device that continuously records movement activity as a correlate of sleep quantity 

and quality. These devices were worn by 9 non-deployed SEALS (NDST), 10 deployed SEALs 

(DST) and 12 submariners (SCG) both before and during Operation Foal Eagle. The results 

from the actigraph data showed that the DST obtained significantly less total sleep per 24hr cycle 

(Total Sleep) during the early phase of the patrol (while in transit) than during the late phase 

(during operations) of the patrol (p<0.01). The main period of sleep per 24hr cycle (Main Sleep) 

for the DST was significantly longer during the late patrol (7.7 hours) phase than during either 

the pre-patrol (5.8 hours; p<0.05) or early patrol (4.0 hours; p<0.01) phases. There were no 

significant differences in the amount of Main Sleep or Total Sleep per 24-hr cycle between patrol 

phases for either the SCG or the NDST. An average of 8 hours per night sustains cognitive 

performance and the ability to comprehend, interpret, adapt and plan in rapidly changing 

circumstances. The DST in this study did not get adequate sleep during the pre-patrol and early 

patrol phases. Our recommendation is that operational commanders should develop effective 

sleep management plans and aggressively communicate to operators the impact of sleep deficits 

on individual and unit performance. 
48

INTRODUCTION 

The Departments of Operational Stress Research, Neurobiology & Behavior, and Biomedical 

Assessment, Division of Neuropsychiatry (Div NP), Walter Reed Army Institute of Research 

(WRAIR) collaborated with the US Naval Submarine Medical Research Laboratory (NSMRL) to 

evaluate sleep in deployed and non-deployed SEALs and Submariners based in Hawaii. During 

this study, WRAIR personnel evaluated sleep in Naval Special Operatorsí by using wrist-worn 

actigraphs. An actigraph is an unobtrusive device usually worn on the non-dominant wrist which 

continuously records arm movement from which sleep periods may be derived. In the 

laboratory, sleep and wakefulness are scored on the basis of concurrent recordings of 

electroencephalogram (EEG), electrooculogram (EOG), and electromyogram (EMG) signals; 

termed polysomnography (PSG). However, PSG is labor and equipment intensive, intrusive, and 

not practical for long term, ambulatory field studies. Actigraphy, on the other hand, is 

unobtrusive and efficient for monitoring sleep objectively, and has been shown to correlate 

highly with PSG-scored sleep/wake states. 

Div NP, WRAIR built its first actigraph in 1974 and has led the way in actigraph 

development. Since 1984, Div NP and Precision Control Design, Inc. (PCD, Inc.), have 

successively fielded smaller, more robust, more powerful devices to measure sleep under 

operational conditions such as (a) in soldiers undergoing Ranger training (Pleban et al., 1990), 

(b) during rotations through the National Training Center (NTC), (c) in studies examining the 

efficacy of sleep-inducing medication during trans Atlantic troop deployment by air (Penetar et 

al., 1989), and (d) in studies of sleep/wake schedules of sailors engaged in solo trans Atlantic 

races (Stampi & Broughton, 1989). 

Adequate sleep is important for effective performance. Sleep loss degrades cognitive 

performance, causing impairment in the ability to comprehend, interpret, adapt and plan in 

rapidly changing circumstances (Belenky et al., 1994). The cumulative effects of restricted sleep 

schedules is loss of productivity, leading ultimately to accidents and catastrophes (Mitler et al., 

1988). In the Gulf War (Operation Desert Shield/Storm), sleep deprivation was a contributing 

factor in motor vehicle accidents, the largest source of injury and death for U.S. Army personnel 

(LTC Gordon D. Griffith, U.S. Army Safety Center, 3 June, 1994, personal communication to 

COL Gregory Belenky). Sleep deprivation was also a contributing factor in incidents of friendly 

fire described by Belenky et al. (1996). The information obtained from our actigraph 

measurements will assist Naval Special Operation Commanders in sustaining and enhancing 

Naval Special Operation performance, effectiveness, and survivability during special operations, 

unconventional warfare, clandestine operations and combat. 

OBJECTIVES 

The primary purpose of the actigraph portion of the study was to provide the Naval Special 

Warfare Command with data pertaining to sleep quantity and quality of deployed Naval Special 

Warfare units during Operation Foal Eagle. 

The secondary purpose was to demonstrate to the Naval Special Warfare community and the 

larger military community the utility, reliability, durability, and unobtrusiveness of wrist 

actigraphy for measuring sleep in personnel in operational environments. 
49

METHOD 

Subjects

All subjects were recruited from SDV Team One and the USS Kamehameha SSN 642, as 

described in the Main Report. Pre-deployment and deployment actigraph data were obtained for 

all subjects. The participants in this study were classified in three groups as follows: the Nondeployed SEAL Team (NDST), the Deployed SEAL Team (DST), and the Submariner Control 

Group (SCG). 

Equipment

The BMA-32 actigraph manufactured by PCD, Inc., Ft. Walton Beach, FL, was used in this 

study. This unit contains 32K of random access memory (RAM) and is capable of collecting and 

storing data for up to 14 days. The actigraphs were set to zero-crossing mode in which the 

movement activity signals are compared against a specified threshold and a count recorded 

whenever the signal crosses the threshold. Cumulative counts of one-minute duration were 

chosen to maximize the discrimination of sleep from wake states. 

Procedure

Data were retrieved from each participantís actigraph approximately every 11 days to prevent 

exceeding the data storage capacity (see Equipment section above). Data were downloaded from 

the actigraph to a secure-access database approximately six times per participant. After each 

download, the actigraph battery was replaced with a fresh one and the actigraph re-initiated and 

returned to the participant. Each participant wore the same actigraph originally issued to him 

during the entire study. 

Actigraph Data

Data collected from the study were transferred to 3 1⁄2î disks for transport to the Department 

of Biomedical Assessment for processing and analysis and was always under the personal 

control of a member of the WRAIR research team. 

Data clearly indicating that the actigraph was worn and recording during sleep periods were 

noted in the analysis of sleep parameters. Sleep periods which contained epochs during which 

the actigraph was not worn or where artifacts were detected, were excluded from data analyses. 

The following four categories of sleep data were determined from the actigraph records: 

(1) Main Sleep amount recorded during the longest period of sleep taken during a 24hr cycle 

(2) Total Sleep amount in a 24hr cycle 

(3) Number of Awakenings during the Main Sleep period 

(4) Total Wake Time during the Main Sleep period 

Main Sleep amount is the longest period of sleep taken during a 24hr cycle. Total Sleep

amount in a 24hr cycle includes Main Sleep and naps that may have been taken in this 24hr 

cycle. Main and Total Sleep amounts are measures of sleep quantity, whereas the Number of 

Awakenings and Total Wake Time during the Main Sleep period are measures of sleep quality. 

 The Number of Awakenings is the number of times movement activity within the main 

sleep period was of sufficient magnitude and duration to be considered awake episodes. The 

Total Wake Time during the Main Sleep period is the sum of all of the time spent in each 

awakening during main sleep in the 24-hr cycle. 

See Figure 1 for an example of sleep/wake determinations and awakenings. 
50

The data were separated into pre-deployment and deployment phases. The pre-deployment 

phase data were collected prior to the submarine deployment and will be referred to as Pre-Patrol 

data. The deployment phase data were further divided into two time periods: an Early Patrol 

phase (transit time) and a Late Patrol phase (operations). 

RESULTS 

Since the number of days each participant contributed to the data set varied, each participant 

was given equal weighting by taking the average of all his sleep data for each phase, i.e., PrePatrol, Early Patrol, and Late Patrol. The processed actigraph data were analyzed statistically 

using an analysis of variance (ANOVA) for each of the measures of Main Sleep and Total Sleep, 

as well as Number of Awakenings and Total Wake Time during the Main Sleep period. Post-hoc 

comparisons among means were conducted using the Tukey/Kramer procedure. Results for the 

Non-deployed SEAL Team (NDST), Deployed SEAL Team (DST), and Submariner Control 

Group (SCG) are presented below. 

Table 1 shows the number of participants in each group with analyzable data and summarizes 

the sleep data (i.e., the hours of sleep during the Main Sleep period and the Total Sleep per 24-hr 

cycle) for all groups during each of the three patrol phases. Activity Count

750 --

500 --

250 --

0 --

A:

WAKE

B:

SLEEP

C:

Awakenings

A: Scored awake periods 

B: Scored sleep periods 

C: Scored awakenings 

Figure 1. Sample actigraph record and corresponding sleep/wake scoring. Awakenings take away 

from Main Sleep time. This sample of an actigraph record clearly distinguishes these periods. 

Sample Actigraph Record 
51

Table 1. Main and Total Sleep (Hours) During Pre-, Early and Late Patrol 

 Patrol Phases 

n Pre-Patrol Early Patrol Late Patrol Significance

Non-Deployed 

SEAL Team 

(NDST) 

8 

Main Sleep 

Per 24hr Cycle 

 7.3 hrs 

(sem=0.32) 

7.6 hrs 

(sem=0.39) 

6.7 hrs 

(sem=0.51) No difference 

Total Sleep 

(Main Sleep + Naps) 

per 24hr Cycle 

 

7.7 hrs 

(sem=0.39) 

8.4 hrs 

(sem=0.50) 

7.5 hrs 

(sem=0.55) No difference 

Deployed SEAL 

Team (DST) 

10 

Main Sleep 

Per 24hr Cycle 

 5.8 hrs 

(sem=0.34) 

4.0 hrs 

(sem=0.28) 

7.7 hrs 

(sem=0.49) 

Pre vs Late p<0.05; 

Early vs Late p<0.01 

Total Sleep 

(Main Sleep + Naps) 

per 24hr Cycle 

 

6.5 hrs 

(sem=0.27) 

5.2 hrs 

(sem=0.46) 

8.4 hrs 

(sem=0.38) 

Early vs Late 

p<0.01 

Submariner 

Control Group 

(SCG) 

12 

Main Sleep 

Per 24hr Cycle 

 5.1 hrs 

(sem=0.40) 

6.2 hrs 

(sem=0.35) 

6.1 hrs 

(sem=0.25) No difference 

Total Sleep 

(Main Sleep + Naps) 

per 24hr Cycle 

 

5.7 hrs 

(sem=0.41) 

6.5 hrs 

(sem=0.31) 

7.2 hrs 

(sem=0.26) No difference 

Main Sleep: Results from the Main Sleep per 24hr Cycle indicated that there were 

significant differences in the amount of Main Sleep obtained between groups (F2,27 = 10.63, 

p=0.0005) and across patrol phases (F2,56 = 5.41, p=0.0075), with a significant overall Group x 

Phase interaction (F4,83 = 12.52, p<0.0001). Specifically, of the three groups during the PrePatrol phase, the NDST obtained substantially more Main Sleep at 7.3 hours than the DST at 5.8 

hours and the SCG at 5.1 hours. The difference in sleep quantity between the NDST and the 

SCG was statistically significant (p < 0.01); that is, the NDST obtained significantly more sleep 

than the SCG during Pre-deployment. Although the NDST obtained more Main Sleep than the 

DST, this difference was not significant, nor was there any significant difference in the Main 

Sleep amount between the DST and the SCG during the Pre-Patrol phase. During the Early 

Patrol phase, the NDST and the SCG did not differ from each other in the amount of Main Sleep 

obtained (7.6 hours and 6.2 hours, respectively), but both obtained significantly more sleep (both 

at p < 0.01) than the DST (4.0 hours). There were no significant differences in the amount of 

Main Sleep among the three groups (range = 6.1 to 7.7 hours) during the Late Patrol phase of the 

operation. Across patrol phases, the DST was the only group with significant differences in the 

amount of Main Sleep obtained across the three phases of the operation. The amount of Main 

Sleep obtained during the Late Patrol by the DST (7.7 hours) was significantly higher than that 

obtained during either the Pre-Patrol phase (5.8 hours; p<0.05) or the Early Patrol phase (4.0 
52

hours; p<0.01), however there was no significant difference in Main Sleep amount obtained 

during Pre-Patrol and Early Patrol. 

Total Sleep: Deficits in normal daily sleep quota can be compensated for by taking naps if 

and when opportunity permits. This is reflected in Total Sleep per 24-hour cycle, in which all 

three groups in all phases of the study showed additions to their Main Sleep obtained per 24-hour 

cycle. Results from the Total Sleep per 24hr Cycle measurement indicated that there were 

significant differences in the amount of Total Sleep obtained between groups (F2,25 = 7.58, 

p=0.003) and across patrol phases (F2,52 = 5.93, p=0.0051), with a significant overall Group x 

Phase interaction (F4,77 = 6.48, p=0.0003). Specifically, while NDST's Total Sleep (7.7 hours) 

was longer than either the DSTís (6.5 hours) or the SCGís (5.7 hours), there were no statistical 

significant differences between groups in the Total Sleep measurement during the Pre-Patrol 

phase. There were also no significant differences between groups for Total Sleep during the Late 

Patrol phases (range = 7.2 to 8.4 hours). During the Early Patrol phase, the NDST obtained 

significantly more Total Sleep (8.4 hours) than the DST (5.2 hours; p<0.01). There were no 

significant differences in the Total Sleep obtained between the NDSR and the SCG nor between 

the DST and the SCG during this phase. Across patrol phases, the DST showed no significant 

differences in the amount of Total Sleep obtained during the Pre-Patrol and the Early Patrol. 

However, the DST showed a significant increase (p<0.01) in the Total Sleep obtained during the 

Late Patrol (8.4 hours) in comparison to the Early Patrol phase (5.2 hours). There were no 

significant differences across patrol phases for either the NDST or the SCG. There was an 

increase in ìnapî length (1.2 hours) during the Early Patrol phase that substantially contributed 

to the Total Sleep for the DST.

Figures 2 and 3 show the comparisons of the three groups, respectively, for Main Sleep and 

for Total Sleep in 24-hour cycles. 

Figure 2. Number of sleep hours during Main Sleep per 24hr Cycle for each study group as 

determined by Actigraphy. NDST = Non-deployed SEAL Team; DST = Deployed SEAL 

Team; SCG = SEAL Control Group. * = significant from Pre-Patrol; + = significant from 

Early Patrol. Error Bars represent ± SEM 

*

Main Sleep per 24hr Cycle

0

2

4

6

8

10

Pre-Patrol Early Patrol Late Patrol

Patrol period

Sleep (hrs)

NDST

DST

SCG

*

+
53

Figure 3. Number of sleep hours during Total Sleep per 24hr Cycle for each study group as 

determined by Actigraphy. NDST = Non-deployed SEAL Team; DST = Deployed SEAL 

Team; SCG = SEAL Control Group. + = significant from Early Patrol. Error Bars represent ±

SEM 

Measures of sleep disruptions are obtained both in terms of average Number of Awakenings 

and average Total Wake Time during the Main Sleep period for each group. These results are 

presented in Table 2. 

Number of Awakenings and Total Wake Time during Main Sleep: There were no significant 

differences in the Number of Awakenings nor Total Wake Time during Main Sleep between 

groups and across patrol phases, with no significant overall Group X Phase interactions. The 

NDST had the greatest Number of Awakenings (11.7) as well as the longest Total Wake Time 

during the Main Sleep period (57.4 minutes) in the Pre-deployment phase, while the SCG had 

the least Number of Awakenings at 7.3 and the shortest Total Wake Time during the Main Sleep 

period at 44.8 minutes. The DST had 10.8 awakenings for a Total Wake Time of 56.6 mins. 

During the Early Patrol phase, the DST and SCG showed a comparable Number of Awakenings 

and Total Wake Times during the Main Sleep period as that seen in the Pre-Patrol phase. 

However, the Number of Awakenings and Total Wake Time decreased (but was not significant) 

for the NDST during this same phase. During the Late Patrol phase, Number of Awakenings and 

Total Wake Time decreased (but not significantly) for the NDST and DST. Number of 

Awakenings for the SCG increased slightly but decreased in the Total Wake Time from that seen 

in the prior two phases. These comparisons are shown graphically in Figure 4 for Number of 

Awakenings and in Figure 5 for Total Wake Time during the Main Sleep period. 

Total Sleep

0

2

4

6

8

10

Pre-Patrol Early Patrol Late Patrol

Patrol Period

Sleep (hrs)

NDST

DST

SCG

+
54

Table 2. Number of Awakenings and Total Wake Time during Main Sleep 

 Patrol Phases

n Pre-Patrol Early Patrol Late Patrol Significance

Non-Deployed SEAL 

Team (NDST) 

8 

Number of Awakenings 11.7 

(sem=1.80) 

10.2 

(sem=2.12) 

9.6 

(sem=1.74) No difference 

Total Wake Time 57.4 mins 

(sem=8.60) 

45.8 mins 

(sem=10.56) 

39.5 mins 

(sem=8.33) No difference 

Deployed SEAL Team 

(DST) 

8 

Number of Awakenings 10.8 

(sem = 1.47) 

10.6 

(sem=1.83) 

9.3 

(sem=1.23) No difference 

Total Wake Time 56.6 mins 

(sem=5.01) 

61.0 mins 

(sem=16.86) 

43.0 mins 

(sem=9.92) No difference 

Submariner Control 

Group (SCG) 

12 

Number of Awakenings 7.3 

(sem=0.83) 

7.6 

(sem=1.65) 

8.2 

(sem=2.14) No difference 

Total Wake Time 44.8 mins 

(sem=13.13) 

45.2 mins 

(sem=10.22) 

35.5 mins 

(sem=2.03) No difference 

Figure 4. Number of Awakenings during Main Sleep per 24hr Cycle for each study group as 

determined by Actigraphy. NDST = Non-deployed SEAL Team; DST = Deployed SEAL 

Team; SCG = SEAL Control Group. Error Bars represent ± SEM 

Awakenings During Main Sleep

0

2

4

6

8

10

12

14

Pre-Patrol Early Patrol Late Patrol

Patrol Period

Number of Awakenings

NDST

DST

SCG
55

Figure 5. Number of minutes spent awake during the Main Sleep per 24hr Cycle for each study 

group as determined by Actigraphy. NDST = Non-deployed SEAL Team; DST = Deployed 

SEAL Team; SCG = SEAL Control Group. 

DISCUSSION 

The results of the actigraph data analysis show that the NDST, with Main Sleep 

averaging 7.3 hours during Pre-Patrol and 7.6 and 6.7 hours during Early and Late Patrol phases, 

obtained the most sleep when compared with the DST and the SCG. The amount of sleep 

recommended by the National Sleep Foundation (1998) is 8 hours as the minimum necessary to 

sustain alertness and optimal cognitive functioning throughout the awake period. The actigraph 

data suggest that the stable work environment of normal 8 hours daytime duty with no additional 

duty demands may have permitted the opportunity for adequate sleep for the NDST. 

Consequently, Main Sleep and Total 24 hr Sleep were better regulated and resulted in both 

longer duration and greater continuity of sleep. Both the DST and the SCG, because of their 

unusual work loads and varying work schedules in preparation and training for the Deployment 

(Pre-Patrol) and the demands exacted by mission requirements during Deployment (Early and 

Late Patrol), may not have had regular sleep schedules. The Main Sleep recorded by the 

actigraph was less than 6 hours during Pre-Patrol and less than 5 hours during the Early Patrol 

(for the DST). The Total Sleep recorded by the actigraph was 6.5 hours or less during Pre-Patrol 

and Early Patrol. Both clearly indicate daily sleep deficits and mounting sleep debt from the ongoing sleep deprivation. However, the impact of less than optimal sleep on operational 

performance is unknown. Although the cognitive test battery showed no significant changes in 

cognitive performance in either the DST or the SCG following the deployment it may be that the 

tests in the cognitive test battery were not sensitive enough to detect the decrements associated 

with sleep deprivation. Alternatively, some of the sleep deprivation from the pre-deployment 

Time spent Awake During Main Sleep

0

10

20

30

40

50

60

70

80

Pre-Patrol Early Patrol Late Patrol

Patrol Period

Time Awake (min)

NDST

DST

SCG
56

and early deployment phases may have been offset by increased sleep during the late deployment 

period. 

 Naps are indicative of the need for compensatory sleep following any sleep deprivation 

and naps may mitigate the decline in performance. Actigraph data suggested that the NDST, 

DST, and the SCG alike compensated for less than adequate Main Sleep periods by taking naps. 

 Awakenings during sleep periods, whether spontaneous or due to external stimuli result 

in loss of sleep. The cumulative effect of even brief awakenings can be detrimental to next day 

performance (Belenky et al., 1994). Sleep fragmentation, defined as the number of awakenings 

and duration of these awakenings, is a matter of concern for both the DSTs and SCGs. 

Fragmentation reduces total sleep duration, a factor determining next day performance. The 

amount of sleep lost from the awakenings for these two deployed groups is equivalent to that lost 

by the non-deployed group (NDST). However, the latter had the opportunity for longer sleep 

periods and thus acquired greater sleep amounts. The less than ideal sleep environment for both 

the DST and the SCG may well have precluded opportunities for adequate sleep. 

As is true of the larger study, care must be taken when interpreting this actigraph study in the 

context that it was conducted on a single submarine unit with SEALs and Submariners from one 

command. 

Safety, welfare and effective performance are issues of paramount importance for all military 

personnel. The cases cited in this report for the rangers, combat soldiers, truckers, and other 

workers, all of whom were experiencing sleep deprivation, offer compelling evidence for 

mandating sleep discipline. This discipline would include the requirement of daily adequate 

sleep quantity (8 hours) and quality (minimal sleep fragmentation) not only to maintain effective 

operational performance, but also to ensure the welfare of all personnel. 

The parameters of training in the military are designed to hone the combat edge of 

individuals and units. This training process must provide participants with tough, realistic 

training that will prepare them for war. During this process, training conditions must place 

participants under conditions that stress them physically, intellectually, and emotionally. While 

exposed to severe environment training conditions, and physically and emotionally challenged 

by time constraints, the safety parameters of training must always be considered. Sleep loss is a 

reality of training and has been documented to be a reality of war. Sleep research affords the 

opportunity to increase leadership understanding, individual safety, and performance in a 

minimally invasive and scientifically appropriate manner. Actigraph research assists 

commanders in understanding the impact of sleep on training performance and safety, and 

provides them insight into the amount of sleep required for individuals and units to remain 

combat effective. Research on sleep enhances the Commanderís ability to hone the combat edge 

of their units thereby keeping the U.S. Armed Forces the best-trained combat force in the world. 

LIMITATIONS 

There were some limitations to use of actigraphy in the current study. In the submarine, an 

unanticipated saturation of the activity signal occurred as a consequence of submarine vibrations 

during certain portions of the operation. These vibrations resulted in rejection of actigraph data 

from the analysis due to uninterpretable results. Nevertheless, we were able to ensure adequate 

sampling of data from most subjects to attain reliable results between subjects and across patrol 
57

phases. A solution to this motion artifact problem is under development. Reconciliation of 

differences in sleep quantity between self-report logs (see Main Report) and objective actigraph 

data may be required in future studies using the motion artifact suppression devices. 

 Additional limitations of the use of actigraphs in this setting relate to the design of the 

device worn. The matchbox sized, rectangular design was viewed as a hindrance to some of the 

operations performed by the personnel (e.g., when parachuting or packing the parachutes). Some 

participants were concerned that the edges of the device would potentially interfere with other 

normal work activities. A related consideration is the bulkiness of the waterproofing box that 

must be secured around the actigraph (which is not currently waterproof) prior to the DSTís 

immersion in the water. In development and testing is a watertight actigraph unit the size and 

thickness of a standard wristwatch with watch function capabilities, which will eliminate the 

waterproofing problem as well as the need to wear two wrist-worn devices. 

CONCLUSIONS 

The Main Sleep recorded by the actigraph was less than 6 hours during Pre-Patrol and less 

than 5 hours during the Early Patrol (for the DST). The Total Sleep recorded by the actigraph 

was 6.5 hours or less during Pre-Patrol and Early Patrol. Both clearly indicate daily sleep 

deficits and mounting sleep debt from the on-going sleep deprivation. Taking naps can 

compensate for inadequate sleep. In the case of the DST and SCG during Deployment, this 

strategy may have been used, resulting in their total daily sleep time exceeding 5 hours. 

Validation of these findings using an improved (i.e., artifact-eliminating) version of the actigraph 

is recommended. 

The amount of sleep lost from the awakenings during the Main Sleep for the two deployed 

groups is equivalent to that lost by the NDST. However, the latter had the opportunity for longer 

sleep periods and thus acquired greater sleep amounts. The less than ideal sleep environment for 

both SEALs and Submariners may well have precluded opportunities for adequate sleep. 

RECOMMENDATIONS 

Operational Commanders should develop effective sleep management plans and aggressively 

communicate to operators the impact of insufficient sleep on individual and unit performance. 

Commanders should also encourage operators to sleep when time permits and does not interfere 

with mission accomplishment. 

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continuous combat operations, In B.M. Marriott, ed., Food Components to Enhance 

Performance, Washington, DC, National Academy Press, pp. 127-135. 
58

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