FA-A-8-10 oWOOC'713 /I44

THE EFFECTS OF PHYSICAL FATIGUE AND ALTITUDE ON

PHYSIOLOGICAL, BIOCHEMICAL, AND PERFORMANCE RESPONSES

E. Arnold Higgins, Henry W. Mertens, Jess M. McKenzie,

Gordon E. Funkhouser, Mary Ann White, and Nelda J. Milburn

Civil Aeromedical Institute

Federal Aviation Administration CQ Oklahoma City, Oklahoma

Reproduced From

Best Available Copy

May 1982

Document is available to the public through the

National Technical-2 lnformation Service,

Springfield, Virginia 22121

Prepared for DTIC

U.S. DEPARTMENT OF TRANSPORTATION ft ELECT1Ew.

Federal Aviation Administration

Office of Aviation Medicine DEC 28t.

•Washington, - D.C. 20591

82 12 28 104.

/
r

NOTICE

This document is disseminated under the sponsorship of the

Department of Transportation in the interest of information

exchange. The United States Government assumes no liability

for its content or use thereof.
Tecimical INeWlp Decumentetien Peg*

|.Rogoett 2O . G ovoernment Accoss~on, No. 3. R&C.*04srt's cotolots No.

FAA-AM-82-10 1A b,* J 79.4 __ _ __ __

4. T.09. "a.d Sw.bt,tle S. Rep•rt Dote

the Effects of Physical Fatigue and Altitude on Physio- May 1982

logical, Biochemical, and Performance Responses 6. Perf.o-.0 ort.i li,,o.. C0de

__________________________________________________ . P.hesfogm nO Oge., aetio Pep.e. N..

E:' Ait-•f Higgins, Henry W. Mertens, Jess H. McKenzie,

Cordon F. Funkhouser. Mary Ann White. and Nelda J. Milbu___ 9. Perfem.. On lwo.e.'.. N..e end Addres 10. Week Un-t Nlo. (TRAIS)

FAA Civil Aeromedical Institute

P.O. Box 25082 11. C.o..e.of Ore., No.

Oklahoma City, Oklahoma 73125

13. Type of eeort , d Period CoVeMd

12. Speorin j Agoey NHom end Addes.s

Office of Aviation Medicine

Federal Aviation Administration OAH Report

800 Independence Avenue, S.W. 11. p.'.ei A"ecy C•de

Washington, D.C. 20591

1S. Svpplostioivy Notes

Work was done under approved tasks AM-A-81-PHY-123 and AM-A-81-PSY-85.

16. Abe,.e.. Twelve healthy young men were evaluated in each of four experimental conditions involving the possible combinations of two exercise conditions given prior to

performance testing (1 h of heavy exercise vs. no exercise) and two altitude conditions (ground level vs. 12,500 ft) which were administered during performance testing.

Performance was measured during a 2h--h test session with the Multiple Task Performance

Battery (MTPB) which involved time-shared performance in monitoring of warning lights

and meters, mental arithmetic, problem solving, and tracking. Heart rate was statistically higher after exercise than after no exercise and statistically higher at

12,500 ft than at ground level. Norepinephrine excretion rate was higher during exercise experiments than during no-exercise experiments. There was no altitude effect

for this measurement. The overall composite score of MTPB performance was significant

ly lower at 12,500 ft than at ground level. The adverse effect of higher altitude vas

greatest in the tracking task. The 1-h period of vigorous physical exercise had no

statistically significant main effect on overall NTPB scores. Residual effects of

exercise resulting in increased arousal may account for the tendency for performance

to be slightly higher in several individual tasks of the HTPB following exercise, and

significantly higher in the case of problem solving. Thu interaction of altitude with

exercise vas also significant in the case of tracking performance. The most important

aspect of the interaction was that tracking performance was significantly better at

12,500 ft following exercise. This finding is possibly due to the increase in cardiovascular circulation induced prior exercise. Possible protection fro" mild hypoxia

by prior exercise and exercise "breaks" should be examined in future research.

17. Key Words Is ii. Disimbwt.n Statement

Aviation environment, Simulation, Hypoxia, Document is available to the public throug Physical fatigue, Complex performance, the National Technical Information Service

Physiology, Biochemistry, Physical exer- Springfield, Virginia 22161

cise

19. Socurity Cleself. (of *Is eot) I11. seeu* t y Clesif. (of tiwo p.,.) 21. No. of P"eg 22. Pries

Unclassified Unclassified 24

form DOT F 1700.7 (.-72) Re9,.dj.tio of c."l.iei.d pose euv.,w.ed
THE EFFECTS OF PHYSICAL FATIGUE AND ALTITUDE ON

PHYSIOLOGICAL, BIOCHEMICAL, AND PERFORMANCE RESPONSES

Although the word is difficult to detine, "fatigue" is almost universally

conceptualized as an undesirable state produced by effort--either the

physical or mental effort of doing work or the effort of maintaining vigi- lance when there in no physical work to be done. Fatigue is an undesirable

state because fatigued individuals tend to commit errors; fatigue can adversely affect not only the accuracy but also the timeliness of performance.

Since Lindbergh's 1927 transatlantic flight, fatigue has been recognized

as a potential threat to flight safety (22). To mitigate this threat, the

Federal Aviation Administration (FAA) in 1964 imposed specific limitations on "duty aloft"' times on the crews of air carriers (10). This regulation limits

annual, monthly, weekly, and daily flight times and specifies minimum numbers

of off-duty hours for a variety of flying schedules.

SThus far, the special problem of fatigue due to circadian desynchronosis

has not been the subject of regulation, but the possible risks from this type

of fatigue have not escaped the notice of Congress (23). A workshop on the

subject was convened by the National Aeronautics and Space Administration

(NASA) in the sumnmer of 1980 (23). The consensus of the participants was

that disruption of normal circadian rhythms could be associated with increas- ing fatigue and that desynchronosis could result from a variety of circumstances, including time-zone crossings and the switching of employees into

unusual work shifts. Participants also concluded that, at present, pilot fatigue can be assessed only in subjective terms and that sleepiness and

lowered arousal cannot easily be distinguished from the fatigue that ensues

from prolonged and/or intense work demands. In any case, they agreed that performance in the beat measure of the deleterious effects of fatigue, and

"error reduction," regardless of the cause of the errors, "would priobably

lead to statistically increased air safety."

With an increased recognition of fatigue as a cause of aviation accidents

have come increased efforts to assess the prevalence of fatigue in aviation

operations. In November 1978, the National Safety Data Branch of the FAA's Flight Standards National Field Office began to include fatigue an a factor

which may have contributed to an accident or incident; from that time to

August 1981 there were 37 accident or incident reports that mentioned fatigue

as a factor. Involved in these 37 instances were 6 airline transport pilots,

19 commercial pilots (including four flight instuctors), and 12 private

pilots. Extrapolation of the data indicates that an accident or incident

Involving fatigue may be expected to occur about once per month. n For

Other data bases permit higher estimates of the current rate of fatiguerelated flying problems. The NASA Aviation Safety Reporting System (ASRS) o_

provides pilots with a channel for giving unofficial reports of incidents 0

occurring in flight. A recent NASA report (19), which wan restricted to

incidents involving air transport flights, cited 425 occurrences of fatiguerelated decrements in flight crew performance. Although a precise time span yon/

fAvlatLbilitY Codes 'Avail andiori

( S Dt-t Special L _ _ _I
for the study was not given, a conservative estimate of 4 years (ASRS became

operational in April 1976) indicates that fatigue-ascribed problems may occur at a rate of about nine per month in air transport flights alone.

A variety of factors may contribute to the development of fatigue. Such

factors include physical exertion, hypoxia, monotony, medical conditions such

as anemia and cardiovascular problems, aging, enforced bed rest, and some factors related to desynchronosis. As an initial step toward our goal of

understanding this poorly defined and complex phenomenon we have investigated

effects of prior physical exertion on some physiological and biochemical

responses and on complex performance during mild hypoxia.

The detrimental effects of hypoxia on performance have been summarized

by McFarland (20), Tune (27), and Ernsting and Sharp (8). In general, the

altitude at which tasks are first affected by hypoxia varies inversely with

task complexity, and well-learned tasks are less sensitive to the effects of

hypoxia than are novel tasks. Absolute visual sensitivity and tasks involving discrimination of visual signal intensity are especially sensitive to

hypoxia and may show decrements at 5,000-6,000 ft (8). Performance in simple

reaction time tasks is unaffected at altitudes below 16,000 ft while choice

reaction time and complex psychomotor tasks can be affected at 10,000-12,000

ft (3,18). Glideslope tracking by pilots during simulated flight was adversely affected at 12,300 ft while localizer tracking and control of airspeed, heading, and vertical speed were affected at 15,000 ft (25). A cognitive task involving mathematical computations was affected at 12,000 ft (1)

while memory tasks were affected at 10,000 ft (21). Since continuous flight

in unpressurized aircraft is permitted at altitudes up to 12,500 ft without

supplemental oxygen, adverse effects on flying performance due to hypoxia

effects ate possible and civilian and military education programs for pilots

alert them to this possibility. There is need for additional research on the

effects of factors which may adversely interact with hypoxia. Physical exertion is one such factor.

The effects of prior physical exertion on subsequent performance at

altitude have not been studied previously. Studies of the effects of prior

exertion on performance aL ground level have found both positive and negative

effects. These studies have examined the effects of both "local exercise" on

responses from the same limb being exercised and "general exercise" involving

larger body areas, usually the lower body. Simple reaction times were found

to increase with amount of local exercise (13,16,26). More complex psychomotor tasks including tracking have shown enhancement of performance at moderate levels of local exercise and decrements occurring at higher levels

(7,28).

General exercise also has produced varying effects on performance. Performance in a simple "tapping" psychomotor task was consistently enhanced by

exercise, even with exercise to exhaustion (7). No effect of general exercise was found in performance of an easy tracking task (11,12), but perform- ance was decreased in more complex psychomotor tasks such as ball throwing

(5) and pistol shooting (9). Davey (6) found an "inverted-U" shaped

2
relationship between general exercise and performance in an auditory recognition task. Schmidtke (25) found a similar relationship of exercise to performance of a clock-monitoring task.

Studies of prior physical exertion have typically reported effects on

performance for relatively short periods following exercise, typically no

more than a few minutes. Only one study has examined longer time periods;

Bonnet (2) studied performance during a 6.5-h march and for 6 h afterward.

Performance deficits occurred during exercise in both psychomotor and cognitive performance aftet 5 h of marching. Recovery was apparent following the

end of the march, but some decrements were still evident 6 h after marching.

No beneficial effects were noted.

Theoretical interpretations of effects of physictl exertion on performance typically involve the mechanisms of physiologict, activation and associated psychological arousal, and physical fatigue. The latter factor has

been used to explain detrimental effects of exercise. Activation level and

associated psychological arousal have been used to account for both decrements

and increments in performance. Performance has been thought to have an

"inverted-U" shaped relationship to activation level (6). This implies that

there is some optimal level of arousal for performance. Several studies

discussed above have observed such a function in the case of dose-effect

curves for exercise. The above findings concerning exercise effects suggest that both beneficial and adverse consequences of physical exertion prior to

flight are possible depending on the kind and amount of exercise and the type

of task in which performance is measured.

The present preliminary research examined some effects of prior strenuous

physical exertion during subsequent mild hypoxia, studying: (i) their possible interaction in performance, (ii) their effects on performance of flightrelated tasks in a complex time-sharing task, and (iii) their effects over a

21⁄4-h period following exercise.

METhODS

Twelve healthy young men served as experimental subjects. All were fully

informed of the experiment and met the selection criteria; each was qualified

by a physician for the FAA Class III medical certificate, and none achieved a

pulse rate greater than 150 beats per minute (bpm) or a systolic blood pressure greater than 200mm Hg after the first 10 min of the exercise test to be

used in the experiment.

Each subject was given five 3-h training sessions on the Civil Aeromedical Institute's (CAMI) Multiple Task Performance Battery (MTPB). After

training, subjects underwent four 4-h experimental sessions held with at least

2 days of rest between successive test sessions. The four test sessions

involved the four possible combinations of two exercise treatments administered before performance testing (exercise vs. no exercise), and two altitude

treatments administered during performance testing (12,500 ft (3,810 m) vs.

ground level) as described in Table I. A 30-min "break" period always occurred

3
ýABLE I. Experiment Schedule

Experiment Time

Condition 0.00 - 1.00 h 1.00 - 1.50 h 1.50 - 3.75 h

Hypoxia

1 Exercise Break Performance Test

at 12,500 ft

No Hypoxia

2 Exercise Break Perforzance Test

at Ground Level

Hypoxia

3 No Exercise Break Performance Test

at 12,500 ft

No Hypoxia

4 No Exercise Break Performance Test

at Ground Level.

between exercise (or rest) periods and performance testing since soame interval would normally be expected between heavy physical exertion and flight.

The exercise condition consisted, in full, of four 10-mmn trials during

which the subject pedaled a bicycle ergom.eter at loads of 30 watts (W) for 2

min, 60 W for 4 min, and 100 W for the last 4 min of the trial. Five-mmn

rest periods followed each trial, so that the total exercise test period was

1-h long. In the no-exercise control condition subjects sat upright in an

armchair without performing work. A 30-mmn "break" period followed the exercise or no-exercise treatment. A hand-steadiness test and a fatigue checklist

were administered at that time.

Exposure to the altitude condition was simulated by an oxygen/nitrogen

breathing mixture equivalent to 12,500 ft (3,810 m) altitude. In the control

condition each subject breathed an oxygen/nitrogen mixture equivalent to Ground

level.

The four experimental conditions, comprising the four possible combinations of the two exercise and the two altitude conditions, were presented in

a different order to each subject so that over all subjects, each condition

followed each other condition an equal number of times.

Multiple Task Performance Battery.

The CAMM TPB was used to measure time-shared performance in up to six

component tasks simultaneously. The MTPB system is computerized; task presentation and data collection are automatic. The test panel displays and

response controls are depicted in Fig. 1. The system has been describ..l in

4
Figure 1. Console of the Multiple Task Performance Battery.

detail (4.). A brief description follows:

Tasks 1 and 2: Monitoring of Red and Green Warning Lights.

This is a choice/reaction time task involving the monitoring of five

green lights (normally on) and five red lights (normally off). The 10

lights are arranged in pairs of green and red. One pair is located in

each corner of the test panel and a fifth is located in the center of

the panel. The light lenses also serve as the pushbutton/switch. The

subject was instructed to push the light/switch whenever the light

changed state. The measure of performance on these tasks is mean

response latency recorded separately for red and green lights.

Task 3: Monitoring of Meters.

This task Involves monitoring four meters whose pointers move at random

around the midpoint of the meter scale. The subject responds ti a shift

in the mean position of the pointer by pressing one of two butto.os under

the meter to report a left or right shift. The four meters are arranged
across the top of the test panel. The performance measure is mean

response latency.

Task 4: Mental Arithmetic.

The subject is required mentally to add two numbers and subtract a third

number from the sum of the first two. All numbers are of two digits.

Answers are recorded by a 10-key response panel. The arithmetic task

display is located in the lower center of the test panel with the keyboard to the right of the display. Performance measures are the mean

response latency and percent correct answers.

Task 5: Two-Dimensional Compensatory TrackinR (TREK).

The tracking task display is an oscilloscope screen mounted in the top

center of the subject's panel. The target on the screen is a dot of

light about 1 mm in diameter. A varying amplitude disturbance is imparted to the target in each dimension; the s..bject attempts to counteract the disturbance, keeping the dot at the screen's center, by moving a

control stick with his/her right hand. Performance is measured in arbitrary units (volts) by analog circuitry in terms of mean vector absolute

error and mean vector root mean square (EMS) error.

Task 6: Problem Solving (PS).

Each test panel is equipped with five response buttons, a "task active"

light, and three "feedback" lights, all located at the left center of the

test panel. The problem is to discover the correct sequence in which to

press the five response buttons. Each button appears only once in a

given nequence. Subjects are instructed to use a trial-and-error procedure and a left-to-right search pattern. An amber feedback light is

illuminated every time a button is pressed to show that the response is

acknowledged by the system. Pressing a button in incorrect order causes

a red light to turn on and stay on until the next correct response is

made. Pushing all five buttons in correct order causes a blue light to

turn on. When a problem is solved, a lapse of 15 sec occurs, following

which the same problem is presented a second time. The subject is expected to reenter the previous solution from memory on the second, or

confirmation, presentation. After another 15 sec a new problem is

presented. Performance measures for this task are: (i) mean response

latencies for the first solution at.d the confirmation stages; and (ii)

the mean number of errors per problem made during the confirmation phase.

MTPB Procedure. A basic 42-mmn schedule of the six MTPB tasks was used.

This 42-min period was divided into three lA-mmn intervals. Tasks 1, 2, and

3 were given throughout the schedule. In the first 14-mmn interval, Task 4

was also active. In the second interval of each period, Tasks 5 and 6 were

also active. In the third interval, Tasks 4, 5, and 6 were also active.

These three interval schedules were named the low, medium, and high workload

conditions, respectively, and were always presented in the same order in each

period.

6
The five practice sessions were each of four 42-mmn periods. The experimental test sessions contained three 42-mmn periods.

Performance was assessed in terms of raw and composite scores for each

task. Composite scores summarized all measures of performance for the particular task. An overall composite score (all tasks) was also obtained. Individual composite scores were calculated as follows: for each measure of

performance on a task, the scores for an individual subject were converted to

standard scores with a mean of 500 and a standard deviation of 100. The task

composite score for each subject and experimental treatment was the mean of,

standard scores on each performance measurement. The sign of scores was

changed, when necessary, so that higher standard scores always indicated

better performance and lower scores, poorer performance. An overall composite

score was also calculated for each subject and treatment by averaging the

composite scores for different tasks so that each task made an equal contribution to the variance. Analyses of task and overall composite scores were

made because they: (i) simplify the evaluation of a large amount of data;

(ii) have been found to be more sensitive to the effects of experimental

conditions than the individual measuremen 'ts of performance; and (iii) have

higher reliability than raw score data on individual performance measures

(4,13).

On experiment days, subjects reported to the laboratory at 1200. Each

subject -mptied his bladder as completely as possible without collection of

urine. The time was recorded and urine was subsequently collected at the end

of each experiment. The volume was recorded and a portion of the sample was

frozen for later analysis of catecholamines (10). The subjects were then

fitted with adhesive chest electrodes which were connected to an electromagnetic tape recorder for continuous heart rate (H(R) recording and for monitoring during the exercise portions of the experiments. A sphygmomanometer cuff

was placid on the right arm of each subject for the monitoring of blood pressure during exercise. Thirty min after the exercise/no exercise period

subjects donned oxygen masks and the performance testing was begun.

RESUUrS

All data were treated by analysis of variance techniques (29).

Heart Rate. The HR data are presented in Fig. 2. During the exercise/

no exercise portion of the experiments there was a highly significant effect

for exercise (2 < .001), with HR almost 40 percent higher during exercise than

during rest. During the performance testing phase HR was significantly higher

(2 .05) for those who had exercised than when they had not. There was also

a significant altitude effect (p < .01), with HR higher during the 12,500 ft

exposure than during the ground level exposure.

Urinary Excretion Rate of Catecholamines. There were no significant

findings for the urinary excretion rate of epinephrine (E) (Fig. 3). There

was no altitude effect for the urinary excretion rate of norepinephrine (NE).

The NE values were significantly higher (y .05) during exercise experiments

than during the no-exercise experiments (Fig. 4)

7
Heart Rate Mean ± Standard Deviation (N 15)

12.0- 120 -

llO p<.Ol 110 - p<.05 p<.Ol

1 I00 100-

S90 90-

•~SO soo• cC1 70 - 70 -

60 - 6 s 0o 

a0 A

Exercise No Exercise No Ground 12,500 ft

Exercise Exercise Level Altitude

L-efore Performance-J ' Performance Period I

Figure 2. Bargraph of Heart Rate as a Function of Experimental

Condition Before and During Complex Performance.

8
Urinary Excretion Rate for Epinephrine.

Mean± Standard Deviation (N-15)

1500- No Significant Difference

1300

1100

CO900

700

500

300

Ground 12.500 ft Exerrise No

Level Altitude Exercise

Figure 3. Bargraph of Urinary Excretion Rate for Epinephri-fe

as a Function of Altitude or Exercise Condition.
Urinary Excretion Rate for Norepinephrine.

Mean ± Standard Deviation (N 15)

4500) No Signif icant Diffterence P<.05

I

4000

3500

3000

S2500 C

2000

1500

1000

Ground 12.500 ft Exercise No

Level Altitude Exercise

Figure 4. Bargraph of Urinary Excretion Rate for NorepInephrine

as a Function of Altitude or Exercise Condition.

10

~~ - -.. . . - .... . . . . . ..

" t L~1 :.. .7 - - : "..

1'
Fatigue Checklist. There were no significant effects of exercise or

altitude on the subjective feeling of fatigue. Variability, however, was

great (Fig. 5).

Subjective Fatigue Checklist

Mean I Standard Deviation

(N • 15)

No Significant Difference f6 l

15 -

14

13

12

0

U

9

8

Exercise No Exercise

Figure 5. Bargraph of Subjective Fatigue Checklist

Scores as a Function of Exercise Condition.

11

]/

/
Hand Steadiness. The only significant finding for the Hand-Steadiness

Test was for subject variability (2~ < .01). The scores ranged from 0 to 218

counts during the 10-mmn test period (Fig. 6).

Hand Steadiness

Mean ± Standard Deviation

(N -15)

+ 100 -No Significant Difference

+80

460-

0+ 40

920

-20

_40 -No Exercise Exercise

Figure 6. Bargraph of-Hand Steadiness Scores

as a Function of Exercise Condition.

Complex Performance.

Composite Score Data. The overall composite score data (means and

standard deviations) are shown for the main effects of exercise, altitude,

and periods, in Table II. Since all tasks did not occur at all workloads,

these data are averaged over workload conditions. Overall performance was

significantly lower (p < .05) at 12,500 ft than at ground level but exercise

had no significant effect. Overall performance declined in the second period

of a session, with recovery occurring in period three to nearly the level of

the first period of the session. However, the effect of periods was not

statistically significant.

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Composite scores (means and standard deviations) for each task are also

shown in Table II for the main effects of exercise, altitude, period, and

workload. These data show that the effect of altitude on overall scores was

due primarily to a statistically significant decline in performance in the

tracking task and nominally lower performance at altitude in all other tasks

except arithmetic.

The main effect of exercise was statistically significant (2 < .05) only

in the case of the problem-solving task. The exercise treatment in that case

had the effect of enhancing performance.

Increasing task workload typically had the effect of decreasing performance significantly (y < .01) in all tasks except the monitoring of red lights.

In the latter case, the effect of workload was not statistically significant.

Performance was similar at the low and high workload levels and lower in those

conditions than in the medium workload condition.

Table III shows the significant interaction of exercise with altitude on

tracking, the only task in which this significant interaction was found. The

20-unit superiority of tracking performance in the no-exercise condition over

the exercise condition at ground level was completely reversed at altitude,

even though performance was generally lower at altitude in both exercise conditions.

TABLE III. Composite Tracking Scoires as a

Function of Altitude and Exercise

Altitude

Ground Level 12,500 ft Mean

Exercise 507 492 499.218

No Exercise 528 473 500.782

Mean 518 482

The only other interaction in composite score data that was statistically

significant (2- < .01) was the interaction of workload with period in the monitoring of green lights as shown in Table IV.z

TABLE IV. Standard Scores for Monitoring of Green

Lights as a Function of Workload and Period

Period

1 2 3

Low 520 515 508

Workload Medium 520 498 495 .-

High 458 466 520

14
Raw Score Data. Raw score means and standard deviations for individual

performance measures in each task are shown in Table V as a function of the

main effects of exercise, altitude, workload, and period. These data show

that the significant effect of exercise on problem-solving performance was

due to a statistically significant beneficial effect on response times during

both solution and confirmation stages of a problem and on errors during confirmation measures. Performance was also nominally better following exercise

in all other measures in other tasks except for response times in monitoring

of green lights and mererfr and in arithmetic percent correct.

The decrease in performance at altitude was significant in both measures

of tracking performance and in mean response latency in the arithmetic task.

Nominal performance decreases at altitude also occurred, with one exception,

in all other measures of performance in other tasks.

Increasing workload consistently caused a decrease in performance in all

tasks but monitoring of red lights. Measures on all tasks except red lightsmonitoring and problem-solving response times typically showed a decline in

performance in period two with recovery in period three. In monitoring of I green lights and meters, in arithmetic response time, and in tracking RMS

errors, performance in the final period was even better than in the first

period. In red-lights monitoring, response times showed a continued increase

over periods, whereas response times continued to improve (decrease) over the

three periods in both solutions and confirmations of the problem-solving task.

The effect of test period was significant only in response latency raw scores

for arithmetic.'

*Several interactions were significant in the raw score data. These are

shown in Table 4.The interaction of exercise and altitude was significant

in the case of Arithmetic response latency and tracking absolute error. The

workload and test period had a significant interaction in the case of greenlights response ýlatency and tracking RMS error. The only other interaction

of significance involved the interaction of exercise with workload for arithmetic percentage correct. No significant second order interactions occurred.

Subjective Rating Scales. Subjects made subjective ratings before and

after each performance testing session regarding attentiveness, tiredness,

- tenseness, boredom, and irritation. The main effects of exercise, altitude,

and time of measurement on subjective ratings are shown in Table VII. The

main effect of time of measurement (before vs. after the performance testing

session) was significant in the case of all scales except attentiveness.

After sessions subjects were significantly more tired, more tense, more bored,

and more irritated. The only significant interaction was the second order

interaction of exercise, altitude, and time of measurement with tiredness, as

shown in Table VIII. This shows that the increase in tiredness after the

performance sessions occurred only at ground level when exercise was given and

only at 12,500 ft when the no-exercise condition was given.

15
-. I

TABLE V. The Main Effects of Exercise, Altitude, Period, and Workload

in Raw Data for the Individual Performance Measures (Raw

Scores) in all Tasks

Exercise Altitude

No Ground 12,500

Exercise Exercise Level ft

Green Lights

Mean Response Mean 3026 3259 2992 329%

Latency (ma) S.D. 1762 1973 1739 1988

Red Lights

Mean Response Mean 1813 1763 1722 1855

Latency (ma) S.D. 1192 1119 1018 1277

Meters

Mean Response Mean 13474 13204 13276 13402

Latency (ma) S.D. 10957 9022 11640 8123

Problem Solving

Solution

Mean Time/ Mean 719 753* 730 743

Response (ms) S.D. 166 225 203 194

Confirmation

Errors Per Mean .484 .669** .573 .579

Confirmation S.D. .558 .671 .644 .603

Mean Time/ Mean 751 788* 770 768

Response (ms) S.D. 224 234 228 232

Arithmetic

Mean Response Mean 8.117 8.294 8.062 8.349**

Latency (sec) S.D. 1.431 1.390 1.378 1.435

Percent Mean 95.6 95.6 95.3 95.9

Correct S.D. 4.2 5.0 4.6 4.6

Tracking

Absolute Mean 791.9 802.9 775.4 819.4**

Error (Vector) S.D. 232.1 204.7 209.7 225.6

RHS Error Mean 108.6 109.2 106.0 111.9**

(Vector) S.D. 22.7 22.0 21.4 23.0

* p <.05

**p <.0l

16

K, I:

3⁄4 - /- . *-*- S.
TABLE V. The Main Effects of Exercise, Altitude, Period, and Workload

in Raw Data for the Individual Performance Measures (Raw

Scores) in all Tasks - Continued

Period Workload

Green Lights 1 2 3 Low Medium High

Mean Response Mean 3167 3257 3004 2882 3057 3489**

Latency (ms) S.D. 1830 2038 1733 1658 1635 2218

Red Lights

Mean Response Mean 1629 1849 1886 1814 1753 1797

Latency (ms) S.D. 911 1217 1289 1214 1166 1085

Meters

Mean Response Mean 13010 14361 12646 10670 12806 16541**

Latency (ms) S.D. 11300 10981 7233 7701 8292 12511

Problem Solving

Solution

Mean Time/ Mean 749 745 715 -. 686 787*

Response (ms) S.D. 214 211 165 159 220

Confirmation

Errors Per Mean .528 .609 .596 -- .433 .720**

Confirmation S.D. .549 .633 .680 -- .432 .742

Mean Time/ Mean 781 772 754 - 692 846*

Response (ms) S.D. 246 235 208 --- 197 236

Arithmetic

Mean Response Mean 8.250 8.567 7.799** 7.412 -- 8.999**

Latency (sec) S.D. 1.324 1.441 1.367 1.015 1.307

Percent Mean 95.6 95.5 95.7 95.7 -- 95.5

Correct S.D. 4.2 4.8 4.8 4.9 - 4.3

Tracking

Absolute Mean 779.8 813.8 798.7 - 728.0 866.9**

Error (Vector) S.D. 227.0 218.4 209.7 -- 213.5 201.5

PIZ5 Error Mean 106.8 109.8 101.2 --- 102.6 115.2**

(Vector) S.D. 23.7 21.8 21.5 21.7 21.2

*p <.05

**p <.01

37

- I,. .
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Table VI. Significant Interactions in Raw Sce're Data

Arithmetic - Z Correct

Workload

Low High

Exercise 95.26 96.03

No Exercise 96.18 94.94

Arithmetic - RT (sec)

Altitude

Ground Level 12,500 ft

Exercise 7.866 8.367

No Exercise 8.258 8.331

Trackins - Abs Error (arbitrary units)

Altitude

Ground Level 12,500 ft

Exercise 785 798

No Exercise 765 841

Green Lights - RT (e"c)

Period

1 2 3

LoW 2.808 2.810 3.029

Workload Ned 2.871 3.087 3.213

Hi 3.822 3.875 2.771

Tracking - RMS Error (arbitrary units)

Period

1 2 3

Med 97.599 104.023 106.218

Workload

Hi 115.904 115.500 114.210

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DISCUSSION

The intent of the protocol was to induce a degree of physical fatigue

prior to a standard performance test period. However, the level of fatigue

produced by the standard exercise routine appeared to be quite variable and

* possibly was related to the level of physical fitness of the subjects. The

exercise level was sufficient to cause a statistically significant rise in

the urinary excretion rate of NE when the exercise condition was compared to

the no-exercise condition. Although several subjects complained of the exercise being "difficult" and of their legs being "tired," they did not register

a significant increase in subjective fatigue for exercise over no exercise.

The high variability on the fatigue checklist following exercise is reflective of the range of physical conditioning of the 12 subjects. The maximum

HR attained, usually during the last 10 min of exercise, ranged from 117 to

172 bpm and served as another indication of the varied levels of fitness

among the subjects.

The 30 min between the end of exercise and the beginning of the performance testing was apparently not adequate for full recovery from the effects

of exercise. This was demonstrated by the fact that the average HR during

the MTPE period was statistically higher after exercise than after no exercise.

The only physiological index indicating an effect of altitude was HR. In

both exercise conditions HR was slightly, but significantly, higher in the

altitude condition. Epinephrine excretion rate was nominally higher at ground

level, on the average, whereas norepinephrine excretion rate was nominally

higher at 12,500 ft.

It was found that a 1-h period of vigorous physical exercise which ended

1/2 h prior to performance testing had little effect on subsequent complex

performance. Analogous bouts of exercise may normally occur in work or recreation prior to flight. The 1/2-h rest period between exercise and testing

was found to be sufficient to prevent adverse effects on the overall index of

MTPJB performance at both ground level and the 12,500 ft altitude. Corollary

physiological measurements during this experiment indicate, however, that

r=:overy from exercise was not complete at the start of performance testing.

Those residual effects of exercise, perhaps resulting in increased arousal,

may account for the tendency of MTPB performance to be slightly higher in

general and significantly higher in the case of the problem-solving task.

* The physiological data, however, are not entirely consistent with that

* hypothesis. Some support is suggested by the higher NE excretion rate and

higher HR after exercise. Mean E and NE excretion rates were noirinally

higher in the ground level condition, consistent with the higher overall level

of performance at ground level as compared to 12,500 ft, but HR was slightly

* lower at ground level.

One important finding was that there was no adverse effect of prior

* exercise at altitude. The level of exercise was high, though of short (1-h)

duration, and apparently sufficient recovery occurred to prevent adverse

effacts.

20
The present study aco: to the body of literature on the effects of altitude (hypoxia) on performance by demonstrating a significant decrement in

* complex (time-shared) performance at the simulated altitude of 12,500 ft.

That altitude is the highest at which pilots may fly continuously without

* supplemental oxygen in unpressurized aircraft. Particularly important was

the large and statistically significant decrement that occurred at 12,500 ft

in tracking, a skill of well-known importance to pilots. At the 12,500 ft

altitude, performance in the first 42-mmn period of testing was similar in

both exercise and no-exercise conditions. Tracking performance dropped off

markedly, however, in the no-exercise condition during subsequent periods of

the test session. Performance was maintained at a much higher level follow-

*. ing exercise as can be seen in Table II in the case of tracking. This finding suggests that the increase in the rate of cardiovascular circulation

induced by the prior exercise may result in protection from hypoxia effects

over an extended period of performance (2; h in this case). Future research

on the effects of exercise and altitude should examine this possibility.

The present demonstration of sensitivity of MTPB performance to mild

hypoxia at the 12,500-ft general aviation altitude adds to the value of the

SIPB for study of the effects of various physiological, pharmacological, and

environmental factors which are thought to interact with hypoxia in the aviation environment.

21

.- - . .. I
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22
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23

4i
29. Winer, B. J. 1971. Statistical Principals in Experimental Design,

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"24

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