DOT/FAA/AM-95/19 

Office of Aviation Medicine 

Washington, D.C. 20591 

19950622 017 

Shift Work, Age, and Performance: 

Investigation of the 2-2-1 Shift 

Schedule Used in Air Traffic 

Control Facilities 

I. The Sleep/Wake Cycle 

Pamela S. Della Rocco 

Crystal E. Cruz 

Civil Aeromedical Institute 

Federal Aviation Administration 

Oklahoma City, Oklahoma 73125 

May 1995 

Final Report 

Th.is doc:ument hru bee21 approved f~r ~ub~c r~lease and sale; its 

distribution 111 unlimited. 

This document is available to the public 

through the National Technical Information 

Service, Springfield, Virginia 22161. 

U.S. Department 

of Transportation 

Federal Aviation 

Administration 
NOTICE 

This document is disseminated under the sponsorship of 

the U.S. Department of Transportation in the interest of 

information exchange. The United States Government 

assumes no liability for the contents or use thereof. 
Technical Report Documentation Page 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AM-95/19 

4. Title and Subtitle 5. Report Date 

Shift Work, Age, and Performance: Investigation 

of the 2-2-1 Shift Schedule Used in Air Traffic 

Control Facilities I. The Sleep/Wake Cycle 

May 1995 

6. Performing Organization Code 

7. Author(s) 8. Performing Organization Report No. 

Pamela S. Della Rocco and Crystal E. Cruz 

9. Performing Organization Name and Address 

FAA Civil Aeromedical Institute 

P.O. Box 25082 

Oklahoma City, OK 73125 

12. Sponsoring Agency name and Address 

FAA Office of Aviation Medicine 

Federal Aviation Administration 

800 Independence Avenue, SW. 

Washington, DC 20591 

15. Supplemental Notes 

16. Abstract 

10. Work Unit No. (TRAIS) 

11. Contract or Grant No. 

13. Type of Report and Period Covered 

14. Sponsoring Agency Code 

Air Traffic Control Specialists (ATCS) work rotating shift schedules for most of 

their careers. Specifically, many work a counterclockwise rotating shift schedule, 

called the 2-2-1, or some variation of the schedule. The 2-2-1 involves rotating 

from two afternoon shifts to two mornings and, finally, to a midnight shift over the 

course of one work week. The purpose of the present study was to investigate sleep 

patterns during this type of rotating shift and the potential cumulative partial 

sleep loss in a laboratory-based synthetic work environment. METHODS. Four groups 

of five male subjects between the ages of 30 to 35 (n-10) and 50 to 55 (n=10) 

participated in the four week study. Subjects were screened on medical and cognitive 

criteria. The Multiple Task Performance Battery (MTPB) was utilized to provide a 

motivating synthetic work environment. Subjects were asked to work three 2-hour 

sessions on the MTPB per eight hour day for the last three weeks of the protocol. 

During the second and fourth weeks, subjects worked day shift (0800-1630). During 

the third week, subjects worked the 2-2-1 schedule. Sleep duration and quality, as 

well as mood, sleepiness and fatigue ratings were reported in log books. Wrist 

activity monitors were used to verify sleep duration. RESULTS. Average sleep 

durations decreased over the week of the 2-2-1 from an average of 7. 6 hours, on 

Sunday night prior to the first afternoon shift, to 3. 0 hours just prior to the 

midnight shift. Comparison of sleep duration for the first week of day shifts 

(excluding weekends) to the 2-2-1 week revealed that total sleep time was 

significantly less for the 2-2-1 week (p<.01). No differences were found between age 

groups. DISCUSSION. Data suggest that sleep management interventions could improve 

adaptation to the quick-rotating shift schedules. This study was the first report 

from a laboratory-based study of ·the 2-2-1. It was part of a research program 

designed to develop fatigue countermeasures for implementation with Air Traffic 

Control Specialists in the field. 

17. Key Words 

Air Traffic 

Shift Work, 

Sleepiness, 

Control Specialists, 

Sleep/Wake Cycle, 

Sleep Quality 

18. Distribution Statement 

Document is available 

through the National 

Information Service, 

Virginia 22161 

19. Security Classif. (of this report) 

Unclassified 

Form DOT F 1700.7 (8-72) 

1

20. Security Classif. (of this page) 121. No. of Pages 

Unclassified 30 

Reproduction of completed page authorized 

to the public 

Technical 

Springfield, 

122. Price 
SHIFT WORK, AGE, AND PERFORMANCE: 

INVESTIGATION OF THE 2-2-1 SHIFT SCHEDULE USED 

IN AIR TRAFFIC CONTROL FACILITIES 

I. THE SLEEP/WAKE CYCLE 

INTRODUCTION 

Because Air T raffle Control (A TC) operations require 24-hour per day staffing, Air Traffic Control 

Specialists (ATCS), in many cases, are faced with shift 

work throughout their careers. ATCSs in the United 

States work a relatively unique rapidly rotating shift 

schedule, the "2-2-1" (Price & Holley, 1990), as well 

as a variety of schedule modifications based upon a 

backward or counterclockwise rotation of shifts. Problems associated with shift work in other populations 

could be expected to be found in the ATCS population. These include issues related to health, family, 

life styles, sleep patterns, performance on the night 

shift, and stress (Moore-Ede, Czeisler, & Richardson, 

1983; U.S. Congress, Office of Technology Assessment [OTA], 1991). The sources of stress include 

sleep deprivation, circadian rhythm disruption, and 

disruption of social interactions (Scott & LaDou, 

1990). Each of these factors has implications for job 

performance. Because of the safety-related nature of 

the ATCS's job, assessing and understanding the 

factors that potentially affect job performance, and 

the manner in which they interact and change with 

age, is critical. 

The 2-2-1 schedule was the focus of this research. 

The 2-2-1 requires ATCSs to work two afternoon 

shifts, followed by two morning shifts, and finally a 

night shift, within a five-day period. The rapid, counterclockwise rotations require that employees arrive at 

work progressively earlier throughout the schedule, 

thereby compressing the work week. In this schedule, 

a 40-hour work week is completed within 88 hours, as 

opposed to the 112 hours required on a straight-day 

schedule, and it results in 80 hours offbetween work 

weeks, compared to 62 hours on straight days. The 

1 

transitions from the afternoons to mornings and from 

the mornings to the night shift involve "quick-turnarounds," with as few as eight hours off between shifts. 

The 2-2-1 schedule raises a number of specific 

issues about shift design, and arguments can be developed both in support of and against the schedule, in 

the context of chronobiological principles. Certain 

researchers in shift work design would not recommend the counterclockwise rotation because of the 

potential for sleep loss, circadian rhythm disruption, 

and possible resultant feelings of fatigue or performance decrements. On the other hand, the schedule 

minimizes employee exposure to the night shift, and 

has been used successfully in ATC facilities for several 

decades. There is little evidence, however, to support 

either position (Turek, 1986). 

This laboratory-based study was designed to investigate empirically the extent to which the 2-2-1 schedule resulted, or failed to result, in sleep and circadian 

rhythm disruption, performance decrements, and 

changes in subjective measures of sleepiness and mood. 

Because age has frequently been found to relate to 

performance inATC (Collins, Boone, &VanDeventer, 

1981) and to be a factor in the amount of sleep 

obtained by night shift workers (Tepas, Duchon, & 

Gersten, 1993), the study included age as a factor in 

the investigation. 

The results of the study will be presented in a series 

of reports covering the following areas: the sleep/wake 

cycle, performance, physiological measures, and subjective measures. This technical report, being the first 

of the series will present: 1) an overview of the issues 

associated with shift work with particular focus on the 

sleep/wake cycle, 2) the study methodology, and 3) 

the findings related to the sleep/wake cycle. 

Dist 

A-- J 

Avail and 1 or 

Special 

·
Shiftwork, Age, and Performance 

Overview 

ATCSs are responsible for ensuring the separation 

of aircraft and expediting the flow of air traffic through 

the National Airspace System (Federal Aviation Administration [FAA] Order 7110.65H). The ATCS's 

job, particularly in the terminal and en route career 

options, requires complex cognitive performance 

which includes activities such as monitoring complex 

traffic patterns to ensure aircraft separation through 

application of established rules and procedures, resolution of potential aircraft conflicts, traffic sequencing, assessing developing weather patterns, and 

providing appropriate adjustments to routing. In 1987, 

Computer Technology Associates, Inc. (CTA) completed a job task analysis that identified 1,4 cognitive/ 

sensory attributes required for performing the tasks of 

extreme or high criticality associated with performance of computer and radar workstation jobs in the 

current ATC system (Ammerman, Bergen, Davies, 

Hostetler, Inman, & Jones, 1987). These included 

coding, movement detection, spatial scanning, filtering, image/pattern recognition, decoding, visualization, short-term memory, long-term memory, 

deductive reasoning, inductive reasoning, mathematical/probabilistic reasoning, prioritizing, and verbal 

filtering. Many of these cognitive abilities have demonstrated circadian variations and susceptibility to 

circadian disruption (Monk, 1990). Therefore, an 

ATCS' s performance of tasks requiring each of these 

specific skills and abilities could be expected to 1) 

demonstrate circadian variability and 2) be susceptible to the disruptive effects of shift work on circadian rhythms. 

The following excerpt from a report to the Aviation 

Safety Reporting System (ASRS), a voluntary reporting system operated by the National Aeronautics and 

Space Administration (NASA), provides evidence that 

some ATCSs perceive shift work to be a contributing 

source of problems. In this situation, the reporting 

ATCS had been involved in an operational error. An 

operational error occurs when an ATCS allows an 

aircraft to get too close to another aircraft, a controlled airspace, or the ground. The controller listed 

three. factors contributing to the incident, including 

2 

shift work-related problems. Specifically noted in the 

following account was the schedule that is the focus of 

the present investigation, the 2-2-1: 

Our facility went to a '2-2-1' schedule this year in which we 

work a combination of evening, day and midnight shifts in 

each week. Many of the controllers wanted this schedule, but 

many of us did not. Unfortunately, those of us who did not 

want it have had it imposed upon us anyway. This is a vety 

specialized schedule designed for resilient people who function normally on 5 or 6 hours of sleep. I am not one of these 

people. Because my work hours change on a daily basis, I 

have become unable to form any normal sleep patterns and 

suffer from bouts of fatigue and insomnia. I know it affects 

the quality of my performance and I know I am only one of 

many. 

A number of similar reports can be found in the 

ASRS. These reports, as well as anecdotal evidence 

from various ATCSs, suggest that shift work, and in 

particular the 2-2-1, may cause perceived excessive 

fatigue, sleep loss, and stress, impacts performance, 

and contributes to operational errors. 

Two opposing lines of reasoning can be proposed 

with regard to the 2-2-1 schedule. Table 1 presents a 

sample 2-2-1 schedule for reference as the arguments 

are developed (Melton & Bartanowicz, 1986). 

Table 1 

The 2-2-1 Shift Schedule 

Day 2-2-1 Hours Between 

1 1600-2400 14 

2 1400-2200 10 

3 0800-1600 14 

4 0600-1400 10 

5 0000-0800 

The case in favor of the 2-2-1 was made in the 

literature by Melton and Bartanowicz (1986). They 

suggested that one advantage of the schedule was that 

four of the five shifts were worked during normal 

waking hours. Therefore, employees could maintain 

relatively stable sleep/wake cycles for the four days of 

the schedule in order to remain day-adapted. In addition, there was only one shift, the night shift, that was 

disruptive to the circadian rhythms. It was argued, 

then, that the 2-2-1 may be less disruptive than other 
schedules that require weekly shift rotations in which 

an employee works one shift for several days, and then 

rotates to a new schedule, such as "straight-five" 

shifts, a rotating schedule in which employees work 

five days on the same shift, have two days offbetween 

work weeks, and then rotate to a different shift for five 

straight work days. Melton and Bartanowicz specifically suggested that the 2-2-1 was better than straightfive shifts. Straight-five shift schedules can result in 

relatively continuous circadian disruption because 

during each five-day work week, the body's circadian 

rhythms may not entrain to one shift until about the 

time the employee rotates to a different shift. Field 

studies comparing the 2-2-1 to rotating straight-five 

shifts found the 2-2-1 to be less stressful (Melton, 

1982, 1985). More recent evidence suggests that even 

employees permanently working straight night shifts 

do not completely adapt to the schedule (Naitoh, 

Kelly, & Englund, 1990). 

Another advantage of the 2-2-1 schedule may be 

that it includes only one night shift per week. This 

minimizes employees' exposure to the problems associated with working the night shift, in addition to 

minimizing the circadian disruption. The placement 

of the 2-2-1 's single night shift at the end of the week, 

precludes any circadian disruption due to the night shift 

from adversely affecting work on the following day. 

Certain characteristics of the 2-2-1 schedule, however, are in contrast to current research recommendations about shift design. Examination of the 2-2-1 

schedule reveals that it is a continuously counterclockwise, rapidly rotating schedule, involving two 

phase-advances of work start times of six hours, each. 

The quick-turn-arounds provide employees with as 

little as 8 hours between shifts in which to get home 

from work, sleep, and return to work. This arrangement has the potential to result in cumulative partial 

sleep loss during the week because of the two quickturn-arounds, as well as circadian rhythm disruption. 

During the transition from the morning shift to the 

night shift, employees' sleep is additionally compromised by forcing a sleep period during the afternoon. 

Sleeping in the afternoon is likely to result in poor 

quality sleep for a variety of reasons, including the 

daylight in the environment, social and family activities, and circadian rhythms being in a phase that is 

3 

Shiftwork, Age, and Performance 

tending toward increasing rather than decreasing alertness. Depending upon the sleep/wake schedule maintained by the employee, the two quick-turn-arounds 

could be equivalent to two phase advances in their 

sleep schedule. In an extreme case, in which an employee failed to maintain sleep/wake patterns conducive to a day-adaptation, sleep patterns could be 

analogous to flying two west to east jet flights across 

six time zones and could be predicted to result in 

symptoms of jet-lag or shift-lag. Placement of the 

night shift at the end of the week, following the phase 

advances and possible induction of shift-lag symptoms earlier in the week could cause adverse additive 

interactions of problems associated with the night 

shift and shift-lag effects. 

Results from the series of CAM I ATC facility field 

studies on the 2-2-1 schedule indicated sleep loss of 

approximately 30 minutes per week on the average in . 

2-2-1 shift workers, as compared to straight-five shift 

workers. In addition, the results indicated thatATCSs 

working the 2-2-1 schedule reported more fatigue 

than those working non-rotating, steady schedules 

(Melton, 1985). 

Sleep/Wake Cycle 

The sleep/wake cycle and its relationship to circadian rhythm disruption is important to the present 

study because the 2-2-1 shift schedule directly disrupts the sleep patterns of employees working the 

night shift, and the phase-advancing properties of the 

schedule may further disrupt the sleep/wake cycle. 

Sleep, in the entrained state, has essentially a 24-hour 

periodicity. Entrainment to this period is related to 

the more or less consistent timing of awaking in the 

morningandgoingto bed at night (Broughton, 1989). 

Sleep duration was found to vary as a function of 

the time of sleep onset in relation to the phase of the 

circadian body temperature rhythm (Czeisler, 

Weitzman, Moore-Ede, Zimmerman, & Knauer, 

1980). In free-running isolation studies, sleep duration was found to be longer when sleep onset times 

were near the temperature peak, and shorter when 

asleep times were closer to the temperature minimum. 

The mean sleep latency test demonstrated a rhythmic 

pattern with two distinct periods of maximum sleepiness occurring in the middle of the afternoon and the 
Shiftwork, Age, and Performance 

middle of the night (Lavie, 1986; Richardson, 

Carskadon, Orau, & Dement, 1982). These findings 

have implications for shift workers on a schedule like 

the 2-2-1. If sleep is attempted when the temperature 

rhythm is rising, a person would have more difficulty 

falling asleep and the duration would be shorter. 

Data reported on the sleep patterns of shift workers 

{Tepas, 1982) indicated that for workers on day shifts, 

sleep occurs just prior to their shift, with a sleep period 

between approximately 2300-0700. Afternoon and 

night shift workers, however, tended to sleep immediately following their shifts. Afternoon shift workers' 

sleep periods were found to occur between approximately 2430-0830, while night shift workers generally slept between the hours of 0900 and 1700. Tepas 

noted that the patterns were similar for permanent 

and rotating shift workers. Workers on the night shift 

exhibited the shortest sleep periods, while afternoon 

shift workers reported the longest total sleep times. 

Phase Shift Studies 

The term, "phase shift," refers to a shift in the 

phasic relationship of circadian rhythms to time. An 

example of such a shift can occur in the sleep/wake 

cycle as a result of a change in exogenous cues, such as 

that which occurs when crossing time zones, or as a 

result of shift work changes that result in a shift in the 

sleep/wake cycle. The sleep/wake cycle or pattern of 

sleep is measured by the time of sleep onset and 

termination {Webb, 1982). Phase advances or delays 

can occur in either or both of these measures, and may 

or may not result in a net change in sleep duration. 

Examples of laboratory-based procedures for phase 

shifting the sleep/wake cycle have included exposure 

to bright lights, administration of melatonin, and 

manipulating the rest/activity periods of subjects by 

asking them to sleep or work at particular times 

(OTA, 1991). 

Taub and Berger {1976) reported a series of studies, 

in which they concluded that maintaining stable sleep 

schedules was of equal or greater importance than 

sleep duration for maintaining performance. In 1973, 

these authors reported a study to examine the effects 

of four consecutive weeks of phase-shifted sleep on 

performance. They allowed normal 7 to 8 hour sleep 

durations; however, they phase-advanced or phase4 

delayed sleep by 2 or 4 hours. Compared to a baseline 

sleep period from 2400 to 0800, all phase-shifted 

experimental conditions resulted in performance deficits on 2 tasks, calculation and vigilance. In follow-up 

studies with normal sleepers (7 to 8 hours per sleep 

period) and "habitual long sleepers" (9.5 to 10.5 

hours per sleep period), Taub and Berger {1976) 

manipulated both phase and duration of sleep. In the 

phase-shifted conditions, sleep was advanced or delayed by 3 hours. All phase-shift conditions resulted in 

speed and accuracy decrements on a vigilance task, 

compared to performance after normal sleep periods 

for each individual. Other studies, particularly those 

on jet-lag {Wegmann & Klein, 1985; Monk, Moline, 

& Graeber, 1988) indicated that interruptions of 

sleep were more detrimental to performance than 

sleep loss. 

Higgins et al. (1975) reported the effects of a 12-

hour phase shift in the work day. Fifteen male subjects, ages 20-28, were asked to work on the Multiple 

Task Performance Battery {MTPB) during the day 

shift for four days. The MTPB provided a synthetic 

work environment in which the influence of various 

stressors, such as a phase shift of the sleep/wake cycle, 

on complex task performance could be systematically 

investigated in the laboratory. Sleep was scheduled for 

2300-0600 during the first 4 days of the study, during 

which time subjects were working normal day shifts. 

Then, after only 3 hours of sleep (21 00-2400) on the 

fifth night, the work schedule was shifted by 12 hours 

to a night shift, for a period of 10 days. During this 

period, subjects slept between 1030 and 1800. No 

changes in the total sleep quantity or quality were 

found on a subjective sleep survey as a result of the 12-

hour phase shift. Performance on the MTPB, however, revealed that decrements in performance were 

found on the day following the short 3-hour sleep 

period: an 8% drop from the first session of the day to 

the last. In addition, performance on the first three 

days· following the phase shift was relatively high 

during four of the five one-hour MTPB sessions, but 

fell off significantly during the last session. The endof-the-day drop in performance was eliminated by 

days 4-6 after the phase shift, with little variation 

across each day. A reversal of the diurnal pattern of 

performance was shown during the last three days of 
the study such that the performance peak after the 

phase shift was shifted 12 hours from the pre-phase 

shift peak. MTPB scores were generally lower on the 

last three days of the study, probably as a result of an 

end-of-the-study effect. Results from a subjective fatigue questionnaire revealed that the total fatigue 

index for each day was not changed by the 12-hour 

phase shift, but nine days were required for a complete 

reversal of the daily pattern reported for fatigue. 

In a follow-up study, Higgins, Chiles, McKenzie, 

Funkhouser, Burr, Jennings, and Vaughan (1976) 

explored different alterations of the sleep/wake cycle. 

This study was designed as a laboratory analog of both 

a six-hour phase advance and a six-hour phase delay. 

Fifteen male volunteers (ages 21 to 30) spent five 10-

hour days training on a Kugelmaschine and the MTPB. 

Then three days of baseline data were collected, during which time subjects slept from 2230-0600 and 

worked a two hours on, two hours off schedule on the 

MTPB, with work times beginning at 0800, 1200, 

1600, and 2000. On the fourth day, each group spent 

time in the CAMI altitude chamber, equivalent to a 

flight from Oklahoma City to London, with a change 

of planes in Chicago. Three groups were established, 

such that one group slept from 0230-0600 on the 

fourth night, worked the schedule as noted above, and 

then returned to the pre-flight sleep time for the 

duration of the study. A second group experienced a 

6-hour phase delay and began sleeping from 0430-

1200 for the remainder of the study, with work times 

beginning at 1400, 1800, 2200, and 0200. The final 

group slept from 2030-2400 on the fourth night and 

then phase-advanced their sleep/wake cycle by 6 hours 

(1630-2400) for the remainder of the study, with 

work times beginning at 0200, 0600, 1000, and 1400. 

This final condition was analogous to a west-to-east 

flight or a quick-turn-around in a work schedule. 

Little difference was found in the physiological and 

biochemical measures between the six-hour-change 

groups. Rephasal time for body temperature for the 

six-hour phase shift was about half of that reported in 

the 1975 (Higgins et al.) study. Performance on the 

MTPB revealed that the phase-advanced group had 

the greatest deficit in performance, while the phasedelayed group had the best post-phase-shift perfor5 

Shiftwork, Age, and Performance 

mance. However, there was a confound in the number 

of hours slept after the "flight" to London, making it 

difficult to generalize these effects. 

Age, Shift Work, and Biological Rhythms 

Akerstedt and Torsvall (1981) suggest that after 

one's age reaches the mid-40s, shift work may suddenly become intolerable. Monk and Folkard (1985) 

suggested a framework of four possible contributory 

factors to aging effects related to shift work: 1) Cumulative adverse shift work effects; 2) general weakening 

of a worker's health and stress coping mechanisms; 3) 

the flattening of circadian rhythms with age; and 4) 

sleep tends to become more fragile and there is a 

tendency toward "morningness." 

Foret, Bensimon, Benoit, and Vieux (1981) investigated the cumulative adverse effects of shift work in 

750 oil refinery shift workers. Workers over age 40 

reported poorer sleep and greater use of sleeping pills 

than younger workers. However, comparing workers 

within the same age group, workers with longer experience with shift work demonstrated poorer sleep 

patterns. Thus, the issue of age is sometimes confounded with length of time working shifts. 

Weitzman, Moline, Czeisler, and Zimmerman 

(1982) reported that the gradual flattening of circadian rhythms with age has been well-documented. As 

noted in previous studies of biological rhythms, amplitude and phase labiliry can be associated with 

difficulty in coping with shift work. Weitzman et al. 

(1982) also discussed the deterioration of sleep patterns with increasing age. This is characterized by 

increased wakenings and a reduction in the total 

number of hours slept. Research has also demonstrated a shift in circadian phases with age toward a 

more morning rype than evening type. 

Mertens and Collins (1986) investigated the interaction of age, sleep deprivation, and altitude on complex performance on the MTPB. Older subjects 

(60-69) demonstrated somewhat lower performance 

and were more affected by workload. There was a 

significant interaction between sleep deprivation and 

altitude that was enhanced by increasing workload. 

However, age was not found to be an exacerbating 

factor. 
Shiftwork, Age, and Performance 

In 1982, Webb and Levy reported age differences 

in performance after an extended period of sleep 

deprivation. In this study, performance of six younger 

men (age 18-22) was compared with performance of 

10 older men ( 40-49) during the second night of sleep 

deprivation. Twelve experimental tests were administered. These included addition, visual search, word 

memory, word detection, reasoning, numerical estimation, object uses, remote associates tests, auditory 

vigilance, and line judgment. The data demonstrated 

that deprivation effects were greater in older subjects 

on tests emphasizing speed of performance, as well as 

those which did not. 

Thus, as employees age, there is reason to expect 

that changes in sleep patterns and biological rhythms 

would result in increased difficulty in <l;dapting to 

different shifts and shift schedules that result in partial sleep loss or circadian disruption. 

Research Hypotheses 

Based upon the application of chronobiological 

principles to the 2-2-1 schedule, it was hypothesized 

that the phase-advancing properties (counterclockwise rotation and quick-turn-arounds) would disrupt 

the sleep/wake cycle and result in cumulative partial 

sleep loss over the course of the 2-2-1 schedule. 

Specifically, it was hypothesized that: 

a) Phase shifts in the sleep/wake cycle would be 

measurable in the asleep and awake times of the 

subjects during the 2-2-1 schedule. 

b) Total sleep duration during the two quick-turnarounds (between the second afternoon shift 

and the first day shift, and between the second 

day shift and the night shift) of the 2-2-1 

schedule would be significantly less than total 

sleep duration when 14 hours were available 

between shifts (between the two afternoon shifts 

and between the two day shifts). 

c) Total sleep time would be significantly less 

during a 2-2-1 work week when compared to 

total sleep time during a day shift work week. 

d) Ratings of sleep quality would be significantly 

lower during the 2-2-1, especially on the second 

quick-turn-around (between the second day 

shift and the night shift) than sleep periods 

during day shift weeks. 

6 

e) Age differences in terms of the sleep/wake cycle 

would result in greater disruption for the older 

age group than for the younger age group. 

The introduction has presented the theoretical 

background from which the 2-2-1 schedule was investigated, along with the hypotheses associated with the 

potential disruption of the sleep/wake cycle investigated in the study. 

Methodology 

A four-week protocol was designed to investigate 

the effects of the 2-2-1 quick-turn-around schedule. 

The first week of the protocol was allocated for subject 

adaptation to wearing physiological monitors 24 hours 

per day. The remainder of the protocol involved an AB-A work schedule design whereby subjects worked 

straight days (0800-1630) during the second week of 

the study, the 2-2-1 schedule during the third week, 

and returned to a straight day schedule for the fourth 

week. A synthetic work environment was created by 

using the MultipleT ask Performance Battery (MTPB). 

The protocol is represented in Table 2. (All times are 

based upon the 24-hour clock notation.) 

To assess the effect of the schedule on performance, 

circadian rhythms and sleep/wake cycles, as well as 

subjective experiences of mood and sleepiness, anumber of measures were collected during the study: 1) 

Performance on the MTPB; 2) physiological measures (core body temperature, heart rate, and activity 

level); 3) daily logs of sleep/wake times and sleep 

quality ratings; 4) neuroendocrine measures; and 5) 

mood and sleepiness scales. As previously noted, only 

the sleep data are presented here. 

Subjects 

Twenty male subjects were selected from two different age groups for this study. Ten subjects were 

between the ages of 30-35, with a mean age of 32.0 

years. These subjects were termed the "Younger" 

group. The second group of 10 subjects was between 

the ages of 50-55, with a mean age of52.4years. These 

subjects comprised the "Older" group. The younger 

age range was selected to be representative of ATCSs 

after reaching full performance level, and the older age 

range was selected because ATCSs must stop controlling 

air traffic when they reach age 56. Subject selection was 
Shiftwork, Age, and Performance 

Table 2 

Study Protocol 

DAYS LABEL PROTOCOL 

Week1 Baseline Adaptation to Vitalog Monitor 

1 B1 0800-0900 

2 B2 0800-0900 

3 B3 0800-0900 

4 B4 0800-0900 

5 B5 0800-0900 

6 W1 

7 W2 

Week2 DAYS1 Straight Day Shift 

8 T1 0800-1630 

9 T2 0800-1630 

10 T3 0800-1630 

11 T4 0800-1630 

12 CD1 0800-1630 

13 W3 

14 W4 

Week3 2-2-1 2-2-1 Schedule 

15 A1 1600-2430 

16 A2 1400-2230 

17 01 0800-1630 

18 02 0600-1430 

19 N 2400-0830 

20 ws 

21 W6 

Week4 DAYS2 Straight Day Shift 

22 CD2 0800-1630 

23 CD3 0800-1630 

24 CD4 0800-1630 

25 CDS 0800-1630 

26 CD6 0800-1200 

LEGEND 

B=Baseline W=Weekend T=Training 

CD=Control DayA=Afternoon Shift D=Day Shift 

N=Night Shift 

7 
Shiftwork, Age, and Performance 

restricted to males in order to minimize cyclic variations that might have interacted with or masked 

circadian variations in female subjects. 

Human Subject Utilization Committee Reviews. 

The study protocol and subject consent forms were 

approved by the University of Oklahoma Institutional Review Board. In addition, the study protocol 

was reviewed and approved through the research review process of the FAA Office of Aviation Medicine. 

Subject Recruitment and Reimbursement. Subjects were recruited and paid by a subject recruitment 

contractor. Subjects received $10 per hour for their 

participation on-site in the laboratory and $25 per day 

for wearing the physiological monitors. This totaled 

approximately $1900 per subject for completion of 

the study. Subjects were paid in two installments: 

upon completion of the first two weeks and upon 

completion of the study. All of the 20 subjects successfully completed the four-week protocol. 

Subject Selection. Selection criteria were designed 

to match subjects on characteristics of the ATCS 

population. These included a medical examination, 

vision test, memory test, measures ofintelligence, and 

questionnaires about sleep, activities, alcohol, and 

drug usage. Other selection criteria were designed to 

minimize attrition rates and included requirements 

for three-year local residency, three personal references, and an on-site interview with research staff. 

Smokers were excluded from the study. Subjects were 

also screened for caffeine, alcohol, and illicit drug use 

through administration of a drug use questionnaire. 

Subjects reporting excessive use of caffeine or alcohol, 

or any illicit drug use, were excluded from the study. 

Initial screening was conducted by the contractor, 

during which time addresses and references were verified, and informed consent was obtained from each 

subject. Subsequent screening assessments were conducted on-site at CAMI. Research staff reviewed the 

informed consent with each subject individually, again 

at the time of the interview. 

To ensure equivalence of health status with the 

ATCS population, subjects were required to meet the 

requirements for the FAA Class II medical examination (14 CFR, Part 67, Federal Aviation Regulations). 

The Class II examination included screening for nor8 

mal cardiovascular functioning (blood pressure and 

heart rate), vision, color vision, and hearing. Vision 

requirements included assessment for 20/20 or better 

in each eye, without correction, or at least 20/100 in 

each eye separately, with correction to 20/20 or better. Subjects were assessed for normal visual fields and 

absence of pathology, as well as normal color discrimination ability. Examinations were conducted by the 

CAMI physician and clinic staff. 

The Shipley Institute of Living Scale (Zachary, 

1986) was used as a measure of intelligence. A minimum WAIS-R equivalent score of 104, or one standard deviation below the mean WAIS-R equivalent 

score of ATCSs (109.8, SD=5.9), was established for 

inclusion in this study, based upon a study of 414 

students entering the FAA Academy A TCS N onradar 

Screen (Della Rocco, Milburn, & Mertens, 1992). 

One exception was made to this criterion for one of 

the younger subjects with a WAIS-R equivalent score 

of 103. This subject was accepted in order to complete 

a group of five subjects by the designated group 

initiation date. The subject successfully met all other 

criteria. 

The Digit Span subtest from the WAIS-R 

(Weschler, 1955) was also administered. A minimum 

capacity to remember five digits was required to 

successfully complete the MTPB code lock task. Subjects were required to recall a minimum of five digits 

on the Forward Digit Span subtest and four digits on 

the Backward Digit Span subtest. Prior studies from 

this laboratory using the Digit Span demonstrated a 

positive correlation between performance on the 

MTPB task and the Digit Span scores (personal communication with Dr. Henry Mertens). 

Horne and Ostberg's (1976) MorningnessEveningness Questionnaire was administered to subjects at the time of screening, although it was not used 

to select subjects. Data were collected to assist in 

interpretation of the results. 

Table 3 presents descriptive statistics from the 

Digit Span, Shipley Institute of Living Scale, and 

Morningness-Eveningness Questionnaire by age 

group. Analysis of variance comparing age group 

means revealed no significant differences between the 

groups on any of these measures. 
Shiftwork, Age, and Performance 

Table 3 

Descriptive Statistics from Subject Screening Questionnaires 

Younger Group Older Group 

Mean SD Mean SD 

Digit Span 

Forward 

Backward 

Shipley Institute of Living Scale 

Verbal 

Abstract 

Combined 

WAIS-R equivalent 

Morningness-Eveningness 

Definite Morning 

Moderate Morning 

Neither Type 

Moderate Evening 

Definite Evening 

7.3 

5.2 

33.2 

32.6 

66.2 

108.2 

57.1 

Subject Demographics. Seventeen of the 20 male 

subjects were Caucasian. Two subjects, one in each 

age group, were African-Americans. One subject in 

the Younger group was American Indian. Fifteen 

subjects were married. Half of the subjects reported 

prior military experience, eight of whom were in the 

Older group. 

One subject held a Master's degree, eight subjects 

had completed a Bachelor's degree, and three subjects 

completed an Associate's degree. Five additional subjects reported having attended college. The remaining 

subjects had completed high school, with the exception of one subject who reported attaining aGED. 

Eight subjects reported being currently employed 

at the time of their participation in the study. Three 

subjects from the Older group were retired. Six of the 

subjects reported previous employment in an aviation-related field. One subject in the Older group was 

a former air traffic controller with the Air Force. 

n=1 

n=4 

n=5 

n=O 

n=O 

9 

0.8 

1.1 

2.6 

3.1 

4.1 

4.0 

8.7 

Sleep Measures 

7.2 

5.5 

34.9 

32.2 

67.1 

110.3 

62.9 

n=1 

n=7 

n=2 

n=O 

n=O 

1.4 

1.3 

2.4 

4.0 

4.8 

4.6 

5.5 

Data on sleep. times, duration, and quality were 

collected as self-report data in subjects' daily logbooks. The following measures were utilized from the 

logbooks: 1) asleep time; 2) awake time; and 3) sleep 

quality ratings. Total sleep time was computed as the 

difference between asleep time and awake time. These 

times were verified by visual inspection of the Vitalog 

accelerometer records and corrected in cases where 

the amount of activity conflicted with the self-reported times. Long awakenings during the reported 

sleep period (30 minutes or more) were subtracted 

from total sleep time. 

Subjects reported sleep quality ratings in the daily 

logbooks upon arising. A sleep quality questionnaire 

used by NASA (Gander, Myhre, Graeber, Andersen, 

& Lauber, 1989) was modified for use in this study. 

The questions and scales were as follows: 1) "Falling 

asleep," from Not Difficult (1) to Difficult (5); 2) 
Shiftwork, Age, and Performance 

"My sleep was," from Not Deep (1) to Deep {5); 3) 

"Arising was," from Not Difficult (1) to Difficult (5);. 

and 4) "I now feel," from Not Rested (1) to Rested (5). 

The responses were rescored so that high scores on each 

question indicated good sleep. Then responses to all four 

questions were summed to give a possible high score of 20. 

Procedures 

The MTPB Laboratory was designed with five 

workstations. Thus, four groups of five subjects completed the protocol between September 1992 and 

February 1993. Each group of five subjects was balanced for subjects from the Older and Younger age 

groups (i.e., one group consisted of two subjects from, 

the Older group and three from the Younger group, 

while the next group consisted of three subjects from 

the Older group and two from the Younger group). · 

Subjects reported to the laboratory from Monday 

through Friday, but continued wearing the portable 

physiological monitor throughout the weekends. Start 

dates for each of the groups varied due to various 

scheduling difficulties. Groups 1 and 3 began their 

protocols as scheduled on a Monday (Day 1). Group 

2 did not begin, however, until Wednesday (Day 3), 

and Group 4 started the study on a Tuesday (Day 2). 

Protocol. On the start date of the four-week protocol, subjects reported to the laboratory from 0800 to 

1200 for orientation and training on use of the Vitalog 

physiological monitoring equipment. The orientation briefing included: 1) A brief summary of research 

issues about shift work, circadian rhythms, the ATCS' s 

job, and previous studies validating the MTPB with 

ATCS students; 2) a formal briefing on the study 

protocol; 3) FAA facility and parking issues; and 4) 

potential applications of findings. 

Subjects were instructed to treat their participation 

as a full-time job, to refrain from drinking alcohol, or 

taking any drugs or medications during the course of 

the experiment without informing the experimenter, 

and that deviation from the protocol could result in 

their termination from the study. Subjects were asked 

to maintain relatively stable sleeping and eating schedules. Phone numbers for the study staff were provided 

to each subject. Subjects were instructed to contact a 

researcher as soon as possible should a problem arise. 

Subjects were issued a Vitalog portable monitor 

10 

{Model 5000) following the orientation. A two-hour 

training session was provided on the appropriate use 

of the equipment. Subjects were issued activity logbooks, which had been modified from NASA logbooks (Gander et al., 1989), and instructed on 

maintaining daily records. Data collected in the logbooks included times associated with sleep and awakenings, sleep quality ratings, mood ratings, activities, 

naps, meals, caffeine intake, physical symptoms, times 

of urinations and bowel movements, and time and 

dosage of any medicine taken. The logbooks were 

used to verify study compliance. 

For the remainder of the first week, subjects reported to the laboratory for approximately one hour at 

0800 each day. Researchers met with each subject 

individually to assess any reported problems, verify 

completion of logbooks, and download physiological 

data to a computer from the Vitalog monitors. 

During the second week, subjects began a three-week 

period of working 8.5 hour days at the laboratory, 

Monday through Friday. Week 2 consisted of straight 

day shifts from 0800-1630. Subjects began training on 

the MTPB on the first day of the second week. By the 

second day of that week, a daily protocol was established. 

Table 4 presents a sample daily protocol for the day shift. 

The procedures were the same during the 2-2-1 schedule. 

Table 4 

Sample Daily Experimental Protocol 

Time Activity 

0800-0830 --------- Arrive at the laboratory and 

download physiological data 

0830-0835 --------- Tracking and Questionnaires 

0835-1035 --------- MTPB Session 1 

1 035-1 045 --------- Tracking and Questionnaires 

1 045-1130 --------- Meal Break 

1130-1135 ---------Tracking and Questionnaires 

1135-1335 --------- MTPB Session 2 

1335-1345 ---------Tracking and Questionnaires 

1345-1405 --------- Break 

1405-141 0 --------- Tracking and Questionnaires 

1410-1610--------- MTPB Session 3 

1610-1615 ---------Tracking and Questionnaires 

1615-1630 --------- Debriefing, supplies 
Table 5 

The Study 2-2-1 Shift Schedule 

Hours 

Day 2-2-1 Between Shifts 

1 1600-2430 13.5 

2 1400-2230 9.5 

3 0800-1630 13.5 

4 0600-1430 9.5 

5 0000-0830 

During the third week of the protocol, the subjects 

worked a 2-2-1 shift (Melton, 1982). The daily protocol detailed in Table 4 was followed during all 

shifts. The 2-2-1 was scheduled as shown in Table 5. 

Subjects returned to working straight day shifts 

(0800-1630) during the fourth and final week of the 

protocol. Only two MTPB sessions were completed 

on the final day of the study, and the remaining time 

was used for collecting equipment and debriefing. 

Design and Data Analyses 

The study was a mixed-model design with one 

between-groups factor and two repeated-measures 

factors. The between-groups factor was age group. 

The within-subjects factors were Day of the study and 

Session (or Sample in the case of neuroendocrine 

measures). Analyses and factorial models were specific 

to each dependent measure. Data analyses were conducted utilizing the SPSS statistical package, version 

4.1 for VAX/VMS. For the majority of the analyses 

the SPSS MAN OVA procedure for repeated measures 

was employed. 

Multiple comparisons were conducted utilizing 

procedures prescribed by Toothaker (1991) when 

significant interactions or main effects resulted from 

the MANOVA. The multiple comparison procedure 

(MCP) involved a series of paired t-tests on planned 

comparisons. The comparisons were developed as a 

result of application of chronobiological principles to 

the 2-2-1 work schedule. The control for probability 

ofType I error was established by referring the t-value 

to a Dunn critical value with parameters df = J(n-1) 

and C = K(K-1)/2, where J equals the number of 

between-subject groups, n equals the number of subjects per group, and K equals the number of repeated 

11 

Shiftwork, Age, mid Performance 

measurements for computation of all pairwise comparisons. If fewer than all possible pairwise comparisons were computed, then C equaled the number of 

planned comparisons (Toothaker, 1991). Each analysis of a dependent measure utilized a slightly different 

factorial design, based upon when measures were collected and the specific hypotheses tested, as follows. 

To test the hypothesis that the 2-2-1 work schedule 

resulted in a phase advance in the sleep/wake cycle and 

cumulative partial sleep loss, two-way, between-subjects, repeated-measures, 2 x 16 MANOVAs were 

computed for sleep measures where the two age groups 

were the between-groups factor and 16 sleep periods 

of the study were the repeated-measures factor. The 

16 sleep periods were selected to parallel the MTPB 

performance analyses. Therefore, the MANOVA included sleep periods from day CD 1 through CD6 (see 

Table 2) and provided for comparison of day shifts to 

each day of the 2-2-1, as well as the weekend days of 

the study. Analyses were computed for 1) asleep time, 

2) awake time, 3) sleep duration, and 4) sleep quality 

ratings. Planned comparisons for asleep and awake 

times and duration included: 1) Comparison from 

one sleep period to the next, beginning with Saturday 

before the 2-2-1 week through Thursday afternoon's 

sleep, to determine phase shifts from one sleep period 

to the next, 2) CD 1, a day shift, to the weekend prior 

to the 2-2-1, 3) weekend sleeps before and after the 2-

2-1, and 4) the first two sleep periods of the recovery 

week to CD 1, and each other. There were a total of 12 

comparisons. A Dunn's critical value of 3.48 for 15 

comparisons with 15 degrees of freedom was used. 

To assess cumulative partial sleep loss between day 

shift weeks and the 2-2-1, mean differences between 

total sleep time during DAYS 1 shifts to total sleep 

time during the 2-2-1 shift, for 1) the total seven-day 

period, 2) the five days of work and 3) non-work days 

were analyzed utilizing 2 (Age) x 2 (Week) MANOV As. 

Planned comparisons for sleep quality ratings involved comparing 1) a day shift sleep, T4-CD1, to a) 

the weekends before and after the 2-2-1, b) each day 

of the 2-2-1, and c) W6-CD2 to examine recovery from 

the 2-2-1 and2) a weekend sleep (CD1-W3) to each day 

of the 2-2-1. There were a total of 15 comparisons. A 

Dunn's critical value of3.48 for 15 comparisons and 15 

degrees of freedom was used for these comparisons. 
Shiftwork, Age, and Performance 

RESULTS group, were not included in analyses of Asleep and 

Awake Times. In the case of the Older subject, he did not 

To test the hypothesis that working the 2-2-1 shift sleep following the night shift, and therefore, had no 

would result in a phase advance of the sleep/wake cycle Awake or Asleep Times. In the case of the Younger 

and cumulative partial sleep loss, three sets of measures subject, sleep patterns were affected by transportation 

were analyzed on the sleep of subjects during the study: requirements during two weeks of the study. Both subsleep patterns, sleep duration, and subjective sleep quality jects were included in analyses of sleep duration and sleep 

ratings. Data from two subjects, one from each age quality ratings. Results of the analyses were as follows. 

Table 6 

Means and Standard Deviations for Asleep Times 

Younger Older Overall 

Mean so Mean so Mean so 

SLEEP PERIOD LABEL 

Baseline 

Thur-Fri B4-B5 2336 1.2 2243 0.7 2309 1.1 

Weekend 1 

Fri-Sat B5-W1 0040 1.9 2250 2.0 2345 2.1 

Sat-Sun W1-W2 0019 1.2 2340 1.5 2400 1.4 

DAYS1 

Sun-Mon W2-T1 2324 0.8 2236 1.0 2300 1.0 

Mon-Tue T1-T2 2249 0.9 2222 1.0 2236 1.0 

Tue-Wedy T3 2318 1.0 2242 0.6 2300 0.9 

Wed-Thur T3-T4 2249 0.9 2251 0.5 2251 0.7 

Thur-Fri T4-C01 2319 1.3 2222 0.8 2251 1.2 

Weekend 2 

Fri-Sat C01-W3 0021 1.6 2324 1.1 2352 1.4 

Sat-Sun W3-W4 0046 1.8 2336 1.8 0011 1.8 

2-2-1 

Sun-Mon W4-A1 0031 1.6 2343 1.7 0007 1.6 

Mon-Tue A1-A2 0207 0.8 0149 0.8 0158 0.8 

Tue-Wed A2-01 0018 1.0 2352 0.5 0005 0.8 

Wed-Thur 01-02 2154 1.3 2127 0.9 2140 1.1 

Thursday 02-N 1649 1.7 1652 1.2 1651 1.4 

Friday Post N 1125 2.8 0944 0.9 1034 2.2 

Weekend 3 

Fri-Sat N-W5 0109 1.7 2307 1.6 0009 1.9 

Sat-Sun W5-W6 0052 1.6 2352 1.7 0022 1.7 

DAYS2 

Sun-Mon W6-C02 0008 1.2 2213 1.2 2310 1.5 

Mon-Tue C02-C03 2321 1.0 2215 0.7 2248 1.0 

Tue-Wed CD3-CD4 2307 1 .1 2236 0.8 2252 1.0 

Wed-Thur CD4-C05 2311 1.0 2210 1.0 2240 1 .1 

Thur-Fri C05-C06 2356 1.2 2226 1.1 2311 1.4 

12 
Shiftwork, Age, and Performance 

Sleep/Wake Cycle deviations for Asleep and Awake times. Data were 

To assess the extent to which the 2-2-1 schedule included from the end of the Baseline week (after all 

disrupted the sleep/wake cycle and served to phase groups had started the protocol) through the end of 

advance subjects working the schedule, the average DAYS2, the final week of the study, including weekAsleep and Awake times were computed, and the ends and the sleep periods before and after the Night 

changes induced by the 2-2-1 work week were exam- shift, but not including any "naps" that were taken in 

ined. Tables 6 and 7 present the means and standard addition to the major sleep period. 

Table 7 

Means and Standard Deviations for Awake Times 

Younger Older Overall 

Mean SD Mean SD Mean SD 

SLEEP PERIOD LABEL 

Baseline 

Thur-Fri B4-B5 0614 1.4 0554 0.6 0604 1.1 

Weekend 1 

Fri-Sat B5-W1 0757 2.1 0718 1.3 0738 1.8 

Sat-Sun W1-W2 0849 2.8 0745 1.0 0817 2.1 

DAYS1 

Sun-Man W2-T1 0530 1.2 0548 0.4 0539 0.9 

Mon-Tue T1-T2 0549 0.7 0543 0.6 0546 0.7 

Tue-Wed T2-T3 0549 0.7 0545 0.3 0546 0.5 

Wed-Thur T3-T4 0545 0.7 0548 0.3 0546 0.6 

Thur-Fri T4-CD1 0600 0.8 0552 0.4 0556 0.6 

Weekend 2 

Fri-Sat CD1-W3 0820 2.7 0751 1.4 0806 2.1 

Sat-Sun W3-W4 0852 2.4 0807 0.9 0830 1.8 

2-2-1 

Sun-Man W4-A1 0817 2.2 0704 1.0 0740 1.8 

Mon-Tue A1-A2 0845 2.4 0821 1.3 0833 1.9 

Tue-Wed A2-D1 0604 0.7 0555 0.2 0600 0.5 

Wed-Thur D1-D2 0431 0.4 0415 0.3 0423 0.4 

Thursday 02-N 1958 2.0 2056 1.9 2027 2.0 

Friday Post N 1534 2.1 1304 1.9 1419 2.3 

Weekend 3 

Fri-Sat N-W5 0857 2.4 0756 1.5 0826 2.0 

Sat-Sun W5-W6 0915 1.8 0813 1.2 0844 1.6 

DAYS2 

Sun-Man W6-CD2 0613 0.2 0545 0.3 0558 0.4 

Mon-Tue CD2-CD3 0603 0.6 0522 0.6 0543 0.7 

Tue-Wed CD3-CD4 0601 0.8 0551 0.5 0557 0.6 

Wed-Thur CD4-CD5 0549 1.0 0555 0.3 0552 0.7 

Thur-Fri CD5-CD6 0612 0.6 0551 0.6 0601 0.6 

13 
Shiftwork, Age, and Performance 

Figure 1 presents a graphic representation of one 

subject's sleep/wake patterns, selected from the younger 

age group as representative of the effects of the 2-2-1 

schedule on the sleep/wake cycle. Work times have 

been displayed, along with sleep times, to provide a 

reference. 

Figure 1 reveals the disruption of the sleep pattern 

by the 2-2-1 schedule. An Age x Days between groups 

repeated-measures MANOVA was computed for the 

Asleep and Awake times to assess the extent to which 

the sleep patterns were altered. The analysis included 

those sleep periods occurring between days CD 1 and 

CD6, including weekends and the afternoon sleep 

before the night shift, resulting in a 2 x 16 MANOV A. 

Tables 8 and 9 present the results of the MANOVA 

for Asleep and Awake Times, respectively .. 

Results of the MAN OVA for Asleep Time revealed a 

significant main effect of Age, .E(1, 16)=7.25, 12<.001, as 

well as Day, .E(15, 240)=186.04, 12<.001. The simple 

main effect of Age indicated that the Older group 

(M=2151) went to sleep approximately one hour before 

the Younger group (M=2250) on the average throughout the study. Planned multiple comparisons revealed 

the following phase-shifting patterns of Asleep Time due 

to the 2-2-1: 

1) Asleep time was significantly later (phase delayed) 

on the A1-A2 sleep <M=0158) than the W4-A1 

sleep (M=0007) by approximately two hours, 

!06)=4.62, 12<.05, as a result of working until 

0030 on the A1 shift. 

2) There were three significant advances in the Asleep 

times of the three sleep periods following the 

phase delay. 

Sleep Patterns 

-sLEEP -woRK 

1800 2000 2200 0000 0200 0400 0600 0800 1000 1200 1400 1600 180< 

TIME 

Figure 1. Sleep/wake patterns and work times for one subject from the younger age group. Data are 

included for the duration of the study protocol from the end of the Baseline week. 

14 
Table 8 

MANOVA Summary Table for Asleep Times 

Source 

of Variation 

Age 

Between Subjects 

Day of Shift 

Age by Day 

Within Subjects 

*p<.OS 

**p<.001 

Table 9 

Degrees 

of Freedom 

16 

15 

15 

240 

MANOVA Summary Table for Awake Times 

Source Degrees 

of Variation of Freedom 

Age 

Between Subjects 16 

Day of Shift 15 

Age by Day 15 

Within Subjects 240 

*p<.OS 

**p<.001 

Sums 

of Squares 

70.01 

154.59 

3670.09 

23.20 

315.64 

Sums 

of Squares 

20.58 

199.30 

4308.99 

36.59 

306.02 

a) Asleep time was significantly earlier (phaseadvanced) on the A2-D1 sleep (M=0005) 

than on the A1-A2 sleep (M=0158) by approximately two hours, 1(16)= 13.61, 12<.05. 

b) Asleep time for the D1-D2 sleep period 

(M=2140) was significantly earlier than the 

A2-D1 sleep period (M=0005), the first 

quick-turn-around, by approximately two 

and one-half hours, 106)=8.71, 12<.05. 

Mean 

Squares 

70.01 

9.66 

244.67 

1.55 

1.32 

Mean 

Squares 

20.58 

12.46 

287.27 

2.44 

1.28 

Shiftwork, Age, and Performance 

F 

7.25* 

186.04** 

N.S. 

F 

N.S. 

225.29** 

1.91 * 

3) There was no significant difference in Asleep 

times between the weekend nights (CD1-W3 

[M=2352] or W3-W4 [M=0011]) and Sunday 

night before the 2-2-1 (W4-A1 [M=0007]), 

suggesting that the night before the start of the 

2-2-1 was treated like a third weekend night, in 

terms of Asleep time. 

4) No significant differences were found among 

weekend Asleep times either before or after the 

c) Asleep time for the D2-N sleep period 2-2-1. 

(M=1651), the second quick-turn-around, 

was significantly earlier than the D1-D2 

sleep period (M=2140) by approximately 

five hours, 1(16)=11.61, 12<.05. 

For Awake time, there was a significant Age x Day 

interaction, .E(l5, 240)= .91, 12<.05, as well as a main 

effect for Day, .E(l5, 240)=225.29, 12<.001. None of the 

planned comparisons for Age x Day reached statistical 

15 
Shiftwork, Age, and Performance 

significance, indicating that the interaction was not 

within the planned investigation of effects of the 2-2-

1. The results of the planned comparisons for the Day 

effects indicated the following: 

1) Subjects awoke significantly later on the weekends than on the day shift. Awake time on the 

Saturday morning (CD1-W3) before the 2-2-1 

(M=0806) was significantly later than the Awake 

time on T4-CD1 (M=0556) by approximately 

two hours, ,t(16)=4.96, 12<.05. Similar patterns 

were found when comparing CD1 to Awake 

times on the remaining weekend days. Awake 

time on W3-W4 before the 2-2-1 (M=0830) 

was approximately two and one-half hours later 

than CD1 (M=0556), .t(16)=7.06, 12<.05. Compared to T4-CD1, the W4-W5 (M=0826), 

,t(16)=6.27, 12<.05, and W5-W6 (M=0843), 

,t(16)=8.76, 12<.05, morning Awake times were 

also significantly later. 

2) There was no significant difference between the 

Awake times on W4-A1 and the other days of 

the weekend before the 2-2-1, suggesting again 

that the Sunday night before the 2-2-1 was 

treated like another weekend night, in terms of 

Awake time. 

3) There were three significant advances in Awake 

time associated with the advancing Asleep times 

during the 2-2-1. 

a) Awake time for the first quick-turn-around 

sleep, A2-Dl, (M=0600) was significantly 

earlier than Awake time for the Al-A2 sleep 

(M=0833) by approximately 2.5 hours, 

!(16)=6.27, 12<.05. 

b) Awake time was also significantly earlier for 

the Dl-02 sleep (M=0423) than for theA2-

Dl sleep (M=0600) by approximately 1.5 

hours, .t(16)=11.04, 12<.05. 

c) Finally, Awake time on the second quickturn-around sleep, before the night shift 

(D2-N) on Thursday afternoon (M=2027) 

was significantly earlier than Awake time for 

the 01-02 sleep (M=0423) by approximately eight hours, ,t(16)=34.30, 12<.05. 

4) There were no significant differences in Awake 

times between weekend mornings before or 

after the 2-2-1 shift. 

16 

5) When subjects returned to the Day shift on C02 

after the 2-2-1, the Awake time was significantlyearlier (M=0558) compared to the Awake 

time for the W5-W6 sleep (M=0844) by approximately 2.75 hours, ,t(16)=8.23, 12<.05. 

Finally, the sleep patterns on the Friday following 

the Night shift were highly variable. Of the 20 subjects, 19 slept on Friday during the day. Of those, 16 

(seven Younger, nine Older) slept in the morning 

with Asleep times ranging from 0840-1115, and Awake 

times ranging from 1100-1700. The remaining subjects (three younger) slept in the afternoon, with 

Asleep times ranging from 1320-1620 and Awake 

times ranging from 1800-1840. One subject from the 

Older group, who remained awake during the day on 

Friday, fell asleep at 0050 on Saturday. 

Sleep Duration 

Measures of sleep duration were assessed to determine 

whether or not the 2-2-1 resulted in cumulative partial 

sleep loss. Means and standard deviations for mean sleep 

duration (MSD) are presented in Table 10. 

Figure 2 presents MSD by day and week of the 

study. Figure 2 shows that daily sleep duration was 

relatively stable during the Baseline (Week 1), DAYS 1 

(Week2), andDAYS2 (Week4), but exhibited a more 

erratic pattern during the 2-2-1. 

Table 11 presents the MAN OVA Summary Table 

for MSD. 

The results of the 2 x 16 MAN OVA revealed a 

significant main effect of Day, E(15, 270)=28.08, 

12<.001 on MSD. Planned multiple comparisons revealed the following: 

I) Weekend MSDs were generally longer than 

work day MSDs. MSD was significantly longer 

for the W3-W4 sleep (M=8.5 hours) before the 

2-2-1, .t(I8)=3.59, 12<.05, and the N-W5 sleep 

(M=8.2 hours) following the 2-2-1, ,t(18)=3.48, 

12<.05, than the T4-CD 1 sleep period before the 

Day shift (M=7.0 hours). 

2) The Sunday night before the 2-2-1 (W 4-Al) was 

treated like a weekend night. MSD on W4-Al 

(M=7.6 hours) was not significantly different 

from W3-W4 (M=8.5 hours), but was significantly longer than the following night's (AlA2) sleep (M=6.4 hours), ,t(18)=3.52, 12<.05. 
Shiftwork, Age, and Performance 

Table 10 

Means and Standard Deviations for Sleep Duration 

Younger Older Overall 

Mean SD Mean SD Mean SD 

SLEEP PERIOD LABEL 

Baseline 

Thur-Fri 84-85 6.5 1.6 7.2 0.7 6.8 1.2 

Weekend 1 

Fri-Sat 85-W1 7.6 1.9 8.3 1.6 7.9 1.7 

Sat-Sun W1-W2 8.5 1.4 7.8 ·1.5 8.2 1.5 

DAYS1 

Sun-Mon W2-T1 6.0 1 .1 7.0 1.1 6.5 1.2 

Mon-Tue T1-T2 7.0 0.8 7.1 1.3 7.0 1 .1 

Tue-Wed T2-T3 6.4 0.9 6.9 0.7 6.7 0.8 

Wed-Thur T3-T4 6.7 0.9 6.9 0.6 6.8 0.8 

Thurs-Fri T4-C01 6.6 1.5 7.3 0.9 7.0 1.2 

Weekend 2 

Fri-Sat C01-W3 8.2 1.9 7.9 1.2 8.1 1.5 

Sat-Sun W3-W4 8.5 2.0 8.4 1.4 8.5 1.7 

2-2-1 

Sun-Mon W4-A1 7.9 1.7 7.2 1.3 7.6 1.5 

Mon-Tues A1-A2 6.4 1.8 6.3 1.1 6.4 1.5 

Tues-Wed A2-01 5.7 1.1 5.9 0.6 5.8 0.9 

Wed-Thurs 01-02 6.6 1.2 6.6 0.9 6.6 1.0 

Thursday 02-N 3.5 1.6 4.0 1.7 3.7 1.6 

Friday Post N 4.1 1.4 3.0 1.6 3.5 1.6 

Weekend 3 

Fri-Sat N-W5 7.7 1.6 8.8 1.3 8.2 1.5 

Sat-Sun W5-W6 8.4 1.7 8.2 1.9 8.3 1.8 

DAYS2 

Sun-Mon W6-C02 6.1 1.1 7.4 1.2 6.8 1.3 

Mon-Tues C02-C03 6.5 1.1 6.9 0.9 6.7 1.0 

Tues-Wed C03-C04 6.9 1.2 7.0 1.1 6.9 1.1 

Wed-Thurs C04-C05 6.6 1.2 7.5 1.2 7.1 1.3 

Thurs-Fri C05-C06 6.4 1.4 7.2 1.2 6.8 1.3 

17 
Shiftwork, Age, and Performance 

Table 11 

MANOVA Summary Table for Mean Sleep Duration 

Source Degrees Sums 

, of Variation of Freedom of Squares 

Age 3.66 

Mean 

Squares 

3.66 

Between Subjects 18 158.81 8.82 

Day of Shift 15 615.62 41.04 

Age by Day 15 30.80 2.05 

Within Subjects 270 394.63 1.46 

**p<.001 

Mean Sleep Duration By Day of the Week 

Week of the Study 

+Baseline +Days 1 * 2-2-1 _._Days 2 

9r---~ ............ .. 

5 ------------------------------ -----------

4 ---------------------------

3~------------------------------------------~ 

Sun Man Tue Wed 

WeekDay 

Thu Fri Sat 

F 

N.S. 

28.08** 

N.S. 

Figure 2. Mean Sleep Duration by day of the week for each of the four weeks of the study over both 

age groups. 

18 
3) There were no significant differences in MSD in 

the middle of the 2-2-1 week, comparing A1-

A2 (M=6.4 hours), A2-D1 (M=5.8 hours), and 

D1-D2 (M=6.6 hours) nights to the T4-CD1 

sleep or among each of those three nights during the 2-2-1. Of note is the fact that, although 

the MSD dropped on A2-D1, the first quickturn-around, it was not a significant drop. 

4) Significant sleep loss did occur just prior to the 

Night shift on the Thursday afternoon sleep 

period. The MSD on Thursday afternoon was 

only 3. 7 hours and was significantly less than 

D1-D2 sleep (M=6.6 hours),_t(18)=7.69, p.<.05. 

5) MSDs on the weekend following the 2-2-1 (NW5 and W5-W6) were not significantly longer 

than the corresponding weekend days prior to 

the 2-2-1 (CD1-W3 and W3-W4). 

To determine if the 2-2-1 schedule resulted in 

cumulative partial sleep loss, subjects' MSDs were 

assessed in a manner similar to a previous ATCS sleep 

study (Saldivar, 1977), which involved three comparisons between DAYS1 and the 2-2-1 weeks: 1) the 

seven-day week, 2) the five-day work week, and 3) 

non-work days. Sleep durations for each period were 

Table 12 

Shiftwork, Age, and Performance 

calculated for the sleep prior to the work or non-work 

period. Therefore, sleep durations used to calculate 

the five-day work week included Sunday night through 

Thursday. During the DAYS1 week, the Thursday 

sleep period was Thursday night; however, during the 

2-2-1, the sleep period was Thursday afternoon prior 

to the night shift. Sleep obtained after the night shift 

on Friday morning was included in the MSD for the 

seven-day week, but not for the five-day work week or 

the non-work days. Non-work days included Friday 

and Saturday nights. Table 12 presents descriptive 

MSD data for each of the three time frames ·by age 

group and by shift schedule (DAYS1 and the 2-2-1). 

A 2 x 2 MAN OVA with age as the between-subjects 

independent variable and mean sleep duration as the 

dependent, repeated measure across the two shift 

weeks, was computed for each of the three comparisons. Comparison of the MSD for the sleep periods of 

the five work days (Sunday through Thursday) revealed that subjects slept significantly less on the 

average during the 2-2-1 shift (M=6.05 hours), E(1, 

18)=11.77, p.<.01, than during DAYS1 (M=6.80 

hours). However, comparison ofMSD across the seven 

days for Sunday through Saturday night revealed no 

Means and Standard Deviations for Mean Sleep Duration by Age Group and Shift Schedule 

DAYS1 (Week 2) 2-2-1 (Week 3) 

Mean (hours) SD Mean (hours) SD 

5 Work Week Days 6.80 .69 6.05* .83 

Younger Group 6.58 .65 6.09 1.04 

Older Group 7.03 .69 6.01 .62 

7 Work and Non-work Days 7.23 .63 7.19 .86 

Younger Group 7.10 .64 7.24 1.05 

Older Group 7.36 .61 7.14 .69 

Non-Work Days 8.29 1.35 8.26 1.29 

Younger Group 8.40 1.74 8.04 1.41 

Older Group 8.19 .89 8.48 1.18 

19 
Shiftwork, Age, and Performance 

significant differences due to the shift schedule worked. 

No significant differences were found in MSD between the non-work days (Friday and Saturday nights) 

following either shift schedule, suggesting that the 

sleep debt, accumulated during the 2-2-1 schedule, 

was made up by sleep following the night shift on 

Friday. No age differences were found. 

Sleep Quality Ratings 

Subjective ratings of sleep quality were recorded for 

each sleep period, except the Friday morning following the Night shift. Two subjects, one from each age 

group, were excluded from the following data for 

failing to complete all ratings. Ratings for the four 5-

point scale items were summed for a total of twenty 

possible points. Lower ratings represented poor sleep 

quality; higher ratings represented good sleep quality. 

Means and standard deviations for combined sleep 

quality ratings are presented in Table 13. 

Table 13 

Table 14 presents the MANOVA Summary Table 

for the combined Sleep Quality Ratings. 

The results of the 2 x 16 MAN OVA for combined 

sleep quality ratings revealed a main effect for Day, 

E(14, 224)=7.22, 12<.001. Planned multiple comparisons revealed: 

1) Compared to a day shift sleep (T4-C01), only 

the 2-2-1's second quick-turn-around 02-N 

sleep quality (M= 11.1) was rated significantly 

lower than the T4-C01 sleep (M= 14.3), 

106)=4.56, 12<.05. 

2) Comparison of each of the 2-2-1 work days with 

a weekend (CD1-W3) sleep (M=16.2) revealed 

significantly lower sleep quality ratings for three 

of the five 2-2-1 sleep periods: A1-A2 (M= 13.3), 

106)=4.28; D1-02 (M=13.2), 106)=3.67; 02-

N (M= 11.1), 1(16)=6.35, 12<.05, indicating that 

for three of the 2-2-1 sleep periods, sleep quality 

was rated poorer than weekend sleep. This was 

Means and Standard Deviations for Combined Sleep Quality Ratings 

Younger Older Overall 

Mean SO Mean SO Mean SO 

SLEEP PERIOD LABEL 

DAYS1 

Thurs-Fri T4-C01 14.1 1.9 14.4 2.8 14.3 2.3 

Weekend 2 

Fri-Sat C01-W3 16.6 2.7 15.9 3.3 16.2 2.9 

Sat-Sun W3-W4 15.1 2.2 15.9 1.7 15.5 1.9 

2-2-1 

Sun-Mon W4-A1 15.1 3.4 14.7 2.6 14.9 3.0 

Mon-Tues A1-A2 13.4 2.7 13.1 2.8 13.3 2.7 

Tues-Wed A2-01 11.9 3.9 14.4 2.4 13.2 3.4 

Wed-Thurs 01-02 14.3 3.0 12.1 3.2 13.2 3.2 

Thursday 02-N 11.7 2.4 10.4 2.2 11.1 2.4 

Friday Post N 

Weekend 3 

Fri-Sat N-W5 15.4 2.8 16.3 2.2 15.9 2.5 

Sat-Sun W5-W6 16.2 2.2 16.3 1.3 16.3 1.8 

DAYS2 

Sun-Mon W6-C02 13.4 4.2 13.7 2.9 13.6 3.5 

Mon-Tues C02-C03 13.9 3.1 14.9 1.7 14.4 2.5 

Tues-Wed C03-C04 14.1 2.7 15.7 2.8 14.9 2.8 

Wed-Thurs C04-C05 14.6 2.2 14.8 3.1 14.7 2.6 

Thurs-Fri C05-C06 14.1 3.9 14.3 2.3 14.2 3.1 

20 
Shiftwork, Age, and Performance 

Table 14 

MANOVA Summary Table for Sleep Quality Ratings 

Source Degrees Sums Mean 

of Variation of Freedom of Squares Squares F 

Age 2.70 

Between Subjects 16 774.13 

Day of Shift 14 484.53 

Age by Day 14 81.91 

Within Subjects 224 1073.42 

**p<.001 

nottrueforeither 1) theDayshiftsleep, T4-CD1, 

or 2) A2-D1, the first quick-turn-around, neither 

of which was found to be rated significantly lower 

than the weekend ratings. 

Each of the sleep quality rating categories was assessed 

to determine which dimensions were identified by the 

subjects as the source of the perceived sleep disruptions. 

MANOV As on each of the four questions resulted in a 

significant main effect for Day, as follows: 1) Difficulty 

in falling asleep E(4, 224)= 3.18, J2<.001; 2) How deep 

was sleep, E(14, 224)=6.62, J2<.001; 3) Difficulty arising, .E04, 224)=3.44; and 4) Rested feeling .E04, 

224)= 5. 90, Jl<. 001. Planned comparisons on each of the 

four questions revealed the following: 

1) For T4-CD1, a day shift sleep, compared to 

D2-N, the quick-turn-around to the night shift, 

results revealed that the afternoon sleep on D2-

N (M=2.22) was not rated as deep as the T4-

CD1 sleep (M=3.78), !(16)=5.50, J2<.05. No 

differences were found, however, for any of the 

other three sleep rating items. 

2) For a weekend sleep, CD1-W3, compared to 

the sleep periods associated with the 2-2-1 shift, 

results revealed that: 

a) For the A1-A2 sleep, subjects reported significantly poorer ratings for difficulty arising (M=2.83) and for how rested they felt 

(M=2.94) than for CD1-W3 ratings of difficulty arising (M=4.17), !06)=4.26, J2<.05; 

21 

2.70 N.S. 

48.38 

34.61 7.22** 

5.85 N.S. 

4.79 

and how rested they felt (M=4.0), !(16)=4.78, 

J2<.05, respectively. 

b) For the D1-D2 sleep, subjects reported significantly greater difficulty falling asleep 

(M=3.06) than for CD1-W3 (M=4.33), 

!06)=3.86, J2<.05. 

c) For the afternoon D2-N sleep, subjects reported poorer sleep quality ratings on all 

four questions than for the weekend, CD1-

W3. Falling asleep was rated more difficult 

on D2-N (M=2.94) than on CD1-W3 

(M=4.33), !06)=4.74, J2<.05. Subjects reported deeper sleep on CD1-W3 (M=3.72) 

than on D2-N (M=2.22),!(16)=4.34,J2<.05. 

Arising was rated more difficult on D2-N 

(M=3.44) than on W3-W4 (M=4.17), 

!06)=3.71, J2<.05. And finally, subjects reported feeling significantly less rested on 

D2-N (M=2.50) than on CD1-W3 

(M=4.00), !06)=4.60, J2<.05. 

d) One additional finding was that subjects 

reported feeling significantly less rested on 

A2-D1 (M=2.78) than on CD1-W3 

(M=4.00), !(16)=4.27, J2<.05. 

3) Sleep ratings for W6-CD2, the sleep prior to 

the first day shift after the 2-2-1, were no 

different on any of the items than forT 4-CD 1, 

suggesting no extended effects of the 2-2-1 

beyond the weekend. 
Shiftwork, Age, and Performance 

Napping Data 

The calculation of sleep duration did not include 

naps or sleeps taken aside from the major sleep of the 

day. However, napping data were collected and are 

summarized as follows: 

Baseline: A total of 23 naps (by 14 subjects) were 

taken from days B3-B5 during the baseline week. 

These naps occurred on days when subjects only had 

to report to the lab for one hour per day. Thirteen of 

the naps were taken by subjects in the Younger age 

group (M= 1.5 hours), and ten were taken by subjects 

in the Older age group (M= 1.1 hours). 

DAYS I. In contrast, only two naps were reported 

during the five days ofDAYSl. A 1.5-hour nap was 

taken by a Younger subject and a .25-hour nap was 

taken by an Older subject. 

2-2-1 Week. Nine naps (by eight subjects) were 

reported during the 2-2-1 work week. Six of these 

were taken on A1, the day of the first afternoon shift. 

The remaining three were taken on A2, the day of the 

second afternoon shift. Of these naps, four were taken 

by Younger subjects (M= 1.9 hours) and five by Older 

subjects (M=.75 hours). 

DAYS2. Six naps (by four subjects) were reported 

during DAYS2. The mean nap time for the Younger 

subjects (n=2) was 1.25 hours. One Older subject 

took a .25-hour nap, while the other did not report the 

actual length of the nap. 

Weekends. Seven naps were reported for the weekend before DAYS1, eight were reported for the weekend before the 2-2-1, and six were reported for the 

weekend before DAYS2. Of these 21 naps, nine were 

taken by five Younger subjects (M= 1. 7 hours) and 12 

were taken by six Older subjects (M=1.2 hours). The 

number of naps reported did not increase on the 

weekend after the 2-2-1 work week. 

DISCUSSION 

This report presented the results of an investigation 

of a unique, rapidly-rotating shift schedule, the 2-2-1, 

commonly used by Air Traffic Control Specialists. 

Application of chronobiological principles to this 

particular work schedule revealed properties that could 

result in opposing positions supporting or discourag22 

ing the use of the schedule. Both positions have 

various implications for the health and job satisfaction of the work force, as well as maintenance of safety 

in the air traffic system. Even though the schedule has, 

over the past two to three decades, been successfully 

used in ATC facilities, reports, such as those from the 

ASRS, can be found to implicate the schedule as a 

source of fatigue and sleepiness. Because air traffic 

control is a safety-related occupation, it was important to investigate the extent to which the 2-2-1 

schedule could result in possible adverse effects, such 

as sleep disruption. 

The results from the sleep pattern data analyses 

supported the hypothesis that the 2-2-1 significantly 

disrupted the sleep/wake cycle. The disruptions were 

primarily in the form of phase-shifting. The 2-2-1 

schedule, in the present study, resulted in one phase 

delay of two hours, followed by two phase advances of 

2- and 2.5-hours each in Asleep times (not including 

the shortened sleep obtained prior to the night shift). 

Similar patterns were found in Awake times. Thus, 

the schedule created a situation analogous to one eastwest, and two sequential west-east flights. The phase 

advances occurred in this study on Tuesday and 

Wednesday nights (before each of the day shifts). 

Although the advances in Asleep and Awake times 

were statistically significant for the second quickturn-around (from the day to the night shift), it was 

not clear how disruptive this was to the subjects. 

On the weekends, subjects awoke significantly later, 

and therefore, obtained more sleep. The Sunday night 

sleep prior to starting the 2-2-1 was similar to the 

other weekend nights for Asleep and Awake times. 

The Asleep and Awake times on the weekend after the 

2-2-1 were very similar to the weekend after a week of 

day shifts, suggesting that weekend sleep patterns 

were not affected by the phase shifts during the 2-2-

1. It should be noted that, although this protocol 

scheduled days off from work to coincide with "normal" weekends, for a proportion of the ATCS work 

force, the days off would not be Saturday and Sunday. 

Finally, a significant age difference was found in 

Asleep times, indicating that the Older group, on the 

average, fell asleep approximately one hour before the 

Younger group over the course of the study. 
The hypothesis that there would be significant 

decreases in the mean sleep durations (MSD) on the 

two quick-turn-arounds was only partially supported 

by the data. The MSD on the first quick-turn-around 

from the afternoon to the morning shift was shortened, but failed to attain statistical significance in the 

present study. The sleep duration on the rapid transition from the Day to the Night shift, however, was 

significantly shortened to 3. 7 hours. Thus, the 2-2-1 

only significantly decreased MSD on the afternoon 

prior to the Night shift, instead of the dual disruption 

that was possible, due to the two quick-turn-arounds. 

The Sunday night sleep, just prior to the first 2-2-

1 afternoon shift, was significantly longer in duration 

than the other days of the 2-2-1 work week. In 

combination with the Asleep and Awake time data, 

this would suggest that Sunday was treated, and could 

be perceived by employees, as a third weekend night. 

Cumulative partial sleep loss was assessed by comparing the MSDs during the first day shift week with 

the 2-2-1 week on three measures: 1) the five days 

prior to each work day, 2) the total seven days in the 

week, which included the weekend after the shift, and 

3) the weekend nights. While sleep debt accumulated 

over the 5 workdays, the subjects made up the deficit 

by sleeping during the day on Friday after the Night 

shift. Based upon the fact that the only significantly 

shortened sleep duration was prior to the Night shift, 

the 2-2-1 schedule could not be characterized as 

resulting in cumulative partial sleep loss in the present 

study. 

Sleep quality ratings generally deteriorated over the 

course of the 2-2-1 week. Sleep was rated on the 

following four dimensions: difficulty falling asleep, 

depth of sleep, difficulty arising, and how rested the 

subjects felt. Scores from these four dimensions were 

combined into an overall sleep rating. Weekend sleep 

periods received the highest quality ratings. The Control Day shifts were not significantly different than 

weekends. After the first afternoon shift (A1) of the 2-

2-1, which ended after midnight, subjects reported 

having more difficulty arising and feeling less rested 

(when compared to a weekend sleep). On the first 

quick-turn-around from afternoon shifts to day shifts, 

subjects reported feeling significantly less rested, as 

23 

Shiftwork, Age, and Performance 

compared to weekend sleep. Even though subjects 

had nearly 14 hours off between Day shifts, the sleep 

pattern was phase-advanced between the first day and 

the second day for the second time by 2.5 hours, and 

subjects reported difficulty falling asleep. 

As anticipated, combined sleep ratings indicated 

that subjects found the afternoon sleep during the 

transition to the Night shift to be the worst. This was 

related, in this group of subjects, to perceived depth of 

sleep when compared to sleep on a control day shift 

(CD I). Compared to weekend sleep quality ratings, 

however, the afternoon sleep of the second quickturn-around was rated significantly lower on all four 

quality rating measures. 

Findings from the present study paralleled those 

from previous studies. Sleep duration over the course 

of the 2-2-1 from this laboratory-based study demonstrated a similar pattern to sleep durations in CAMI 

studies fromATC field facilities (Saldivar et al., 1977; 

Melton, 1985). In the previous CAMI studies, however, sleep duration was significantly reduced for the 

sleep associated with Day shifts, which included the 

first quick-turn-around. Similar findings were recently reported from ATC field facility studies by 

Schroeder, Rosa, and Witt (1995) in which sleep 

duration declined throughout the 2-2-1 week. This 

was probably associated with ATC field facility Day 

shift start times before the 0800 start time on the first 

2-2-1 day shift in this study. Early morning shift start 

times have been demonstrated to result in shortened 

sleep durations (Folkard, 1989). As with the Saldivar 

study ( 1977), the data in the present study on sleep 

duration suggested that any sleep debt accumulated 

during the 2-2-1 was recovered by the end of the 

weekend following the 2-2-1. 

The most important finding from the present study 

was the demonstration of the impact of the 2-2-1 on 

the subjects' sleep/wake cycles. None of the previous 

studies had addressed the phase-shifting issues associated with the 2-2-1 schedule. Taub and Berger (1973, 

1976) conducted a series of phase shift studies, in 

which they concluded that maintaining stable sleep 

schedules was of equal or greater importance than 

sleep duration to maintenance of performance. Phase 

shifts from these studies ranged from 2 to 4 hours in 
Shiftwork, Age, and Performance 

both phase-advancing and phase-delaying directions. 

All phase-shifted conditions resulted in speed and accuracy decrements on a vigilance task, compared to performance after sleep periods normal for each individual. 

Even though the 2-2-1 was found to substantially 

disrupt sleep patterns, performance decrements were 

apparent only on the night shift. (Performance data 

will be presented .in the next report in this technical 

report series.) The hypothesized sleep loss and performance decrements following the first quick-turnaround were not supported in the present study. The 

sleep literature was examined for an explanation for 

this finding. Naitoh (1992) proposed the notion of 

"sleep quantum", or the amount of sleep needed by an 

individual for efficiently performing a day's work. In 

reviewing the partial-sleep-deprivation literature, 

N aitoh cited a current proposal that between from 4. 5 

to 5.5 hours of continuous sleep (the sleep quantum) 

should be taken, and that to prevent decrements in 

vigilance performance, a minimum of 4 hours of sleep 

is necessary. Examination of the sleep durations in the 

present study revealed that the sleep period just prior 

to the first turn-around was 5.7 hours, exceeding the 

4-hour threshold. Sleep duration on the second quickturn-around to the night shift (3.7 hours), however, 

fell below the 4-hour minimum. 

Because this was a laboratory-based study with 

such a restrictive protocol, caution should be used in 

generalizing the results. The ARTCC field data collected recently suggested that the 2-2-1 schedule, as 

implemented in the field, was more stable, such that 

the work start times were more likely to be the same 

for the two afternoon shifts and for the two day shifts, 

respectively, as opposed to the 2 hour advances used 

in this study (Cruz & Della Rocco, 1995). Thus, 

employees would start both day shifts at 0600, rather 

than changing from an 0800 start time to an 0600 

start time, as was done in this laboratory study. Analyses of the field study data suggested that the phaseshifting properties of the schedule were not as dramatic 

in employees who regularly work a 2-2-1 schedule as 

that observed in the present laboratory-based study, 

and that employees may adapt by stabilizing their 

sleep/wake patterns. On the other hand, consideration 

of individual differences might reveal greater disruptions 

in sleep patterns than were revealed in either study. 

24 

The present study was an improvement upon methodological problems inherent in a number of circadian performance studies. Instructions to subjects 

were to maintain stable sleep/wake patterns, mealtimes, and activities throughout the study. Daily 

logbooks, in conjunction with accelerometer data 

from the Vitalogs, were used to monitor compliance 

with the protocol during the study. Noncompliance 

was cause for dismissal from the study. Meals and 

breaks were provided at the same point in the work 

day, although subjects were not as well controlled 

outside of the laboratory work sessions. The A-B-A 

protocol was designed to ensure that subjects were 

day-oriented for one full week prior to introduction of 

the 2-2-1 schedule. Circadian core body temperature 

rhythms were measured during the study to verify the 

day-orientation. These data will be presented in one 

of the subsequent technical reports on this study. Selfreports of sleep data were validated in the present 

study through comparison to accelerometer data provided from the Vitalog physiological monitors. 

The study was conducted using non-ATC subjects 

in a laboratory environment; therefore, the results 

may be conservative estimates of the effects of the 2-

2-1. However, it was encouraging that the sleep patterns were similar to field studies with ATC personnel. 

Thus, the results obtained from this study should have 

applicability to serve as a basic foundation for developing of a research program on countermeasures and 

coping strategies. 

The findings related to age differences were minimal in the present study. A possible explanation for 

this finding may be related to subject instructions to 

both groups that they maintain the most stable sleep 

patterns possible during the study. In addition, the 

Older group was selected to fall within the working 

ages of actual ATCSs. Therefore, the Older group was 

only 50-55 years old in this study. It is possible that 

age-related sleep changes were not observable in this 

particular group of subjects. 

As a result of the findings in the present study, three 

areas were suggested for examination as candidates for 

countermeasures. These include the development of 

direct interventions to improve alertness on the night 

shift (bright light exposure and/or napping), sleep 

management education for employees, designed to 
coincide with the basic tenants of the 2-2-1 schedule 

design, and finally, schedule redesign to minimize the 

number of quick-turn-arounds. 

Sleep management is a critical concept for effective 

coping strategies with the 2-2-1 schedule. One of the 

basic tenants of the 2-2-1 (Melton & Bartanowicz, 

1986) is that employees can maintain a day-orientation. The results of the present study, however, call 

this purported stability into question. Thus, employees should be instructed about the importance of 

maintaining a stable sleep/wake schedule, even on 

days off from work. This includes standardizing arise 

times, as well as times for exposure to sunlight in the 

mornings to maintain the timing of the biological 

clock (OTA, 1991). 

Under the category of sleep management, it might 

be possible to improve the quality of sleep during the 

afternoon on the quick transition between the day and 

night shifts. The afternoon sleep quality could be 

enhanced by a) improving the sleep environment 

(ensuring complete darkness and quiet in the room), 

and b) initiating the sleep period earlier, thereby 

providing a greater opportunity for the individual to 

fall asleep, as well as increasing the duration of the 

sleep period. 

The present study addressed only the acute effects 

of working one week of the 2-2-1 schedule. Future 

research should address the effects of working a quickturn-around schedule on a chronic basis, as well as 

identification of individual differences in adaptation 

to the quick-turn-around schedules. 

REFERENCES 

Akerstedt, T. & Torsvall, L. (1980). Age, sleep and 

adjustment to shift work. In W.P. Koella (Ed.), 

Sleep (pp. 190-194). Basel, Karger. 

Ammerman, H., Bergen, L., Davies, D., Hostetler, C., 

Inman, E., & Jones, G. (1987). FAA air traffic 

control operations concepts. Volume VI· ARTCC/ 

HOST en route controllers. (DOT/FAA/AP-87-

01). Washington, DC: Federal Aviation Administration. 

25 

Shiftwork, Age, and Performance 

Broughton, R. (1989). Chronobiological aspects and 

models of sleep and napping. In D.P. Dinges & 

R.J. Broughton (Eds.), Sleep and alertness: 

Chronobiological medical and behavioral aspects of 

napping(pp. 71-98). New York: Raven Press. 

Collins, W., Boone,]., &VanDeventer, A. (1981). The 

selection of air traffic control specialists: History 

and review of contributions by the Civil Aeromedical Institute, 1960-80. Aviation, Space, and 

Environmental Medicine , .22 (April), 217-240. 

Cruz, C. & Della Rocco, P. (1995). Sleep patterns in air 

traffic controllers working rapidly rotating shifts: A 

field study (DOT/FAA/AM-95/12). Washington, 

D.C.: Federal Aviation Administration, Office of 

Aviation Medicine. 

Czeisler, C., Weitzman, E., Moore-Ede, M., Zimmerman, J., & Knauer, R. (1980). Human sleep: 

Its duration and organization depend on its circadian phase. Science, 210 (Dec.), 1264-1267. 

Della Rocco, P., Milburn, N., & Mertens, H. (1992). 

Comparison of performance on the Shipley Institute 

of Living scale, air traffic control specialist selection 

test, and FAA Academy screen (DOT/FAA/AM92/30). Washington, DC: Federal Aviation Administration, Office of Aviation Medicine. 

Federal Aviation Administration. (1994). Air traffic 

control. Federal Aviation Administration Order 

7110.65H(Change 1). Washington, DC: Federal 

Aviation Administration, Air Traffic Rules and 

Procedures Service, Procedures Division. 

Folkard, S. (1989, July). Shiftwork-a growing occupational hazard. Occupational Health, pp. 182-186. 

Foret,]., Bensimon, G., Benoit, 0., &Vieux, N. (1981). 

Quality of sleep as a function of age and shiftwork. 

In A. Reinberg, N. Vieux, & P. Andlauer (Eds.), 

Night and shift work: Biological and social aspects, 

(pp. 149-154). Oxford: Pergamon Press. 

Higgins, E., Chiles W., McKenzie, J., Funkhouser, G., 

Burr, M., Jennings, A., & Vaughan, J. (1976). 

Physiological biochemical and multiple-task-performance responses to different alterations ofthe wakesleep cycle (DOT/FAA/AM-76-11). Washington, 

DC: Federal Aviation Administration, Office of 

Aviation Medicine. 
Shiftwork, Age, and Performance 

Higgins, E., Chiles W., McKenzie, J., larnpietro, P., 

Winget, C., Funkhouser, G., Burr, M.,Vaughan, 

J., & Jennings, A. (1975). The efficts of a 12-hour 

shift in the wake-sleep cycle on physiological and 

biochemical responses and on multiple task performance (DOT/FAA/AM-75-10). Washington, DC: 

Federal Aviation Administration, Office of Aviation Medicine. 

Horne, J. & Ostberg, 0. (1976). A self-assessment 

questionnaire to determine morningnesseveningness in human circadian rhythms. International journal ofChronobioloby, 1, 97-110. 

Lavie, P. (1986). Ultrashort sleep-waking schedule. III. 

"Gates" and "forbidden zones" for sleep. 

Electroencephalography and Clinical Neurophysics, 

QJ, 414-425. 

Melton, C. (1982). Physiological stress in azr traffic controllers: A review (DOT/FAA/AM-82-17). Washington, DC: Federal Aviation Administration, 

Office of Aviation Medicine. 

Melton, C. (1985). Physiological responses to unvarying 

{steady)and2-2-1 shifts: Miami International Flight 

Service Station (DOT/FAA/AM-85-2). Washington, DC: Federal Aviation Administration, Office 

of Aviation Medicine. 

Melton, C. & Bartanowicz, R. ( 1986). Biological rhythms 

and rotating shiftwork: Some considerations for air 

traffic controllers and managers (DOT/FAA/AM86-2). Washington, DC: Federal Aviation Administration, Office of Aviation Medicine. 

Mertens, H. & Collins, W. (1986). The effects of age, 

sleep deprivation, and altitude on complex performance. Human Factors, 28 (5), 541-551. 

Monk, T. (1990). Shiftworker performance. InA. Scott 

(Ed.), Occupational Medicine: State of the Art 

Reviews,2(2): 183-198. Philadelphia,PA: Hanley 

& Belfus. 

Monk, T. & Folkard, S. (1985). Individual differences 

in shiftwork adjustment. InS. Folkard & T. Monk 

(Eds.), Hours of work: Temporal factors in work 

scheduling, ed. S. Folkard and T.H. Monk (pp. 

227-237). New York: John Wiley & Sons Ltd. 

Monk, T., Moline, M., & Graeber, R. (1988). Inducing 

jet lag in the laboratory: Patterns of adjustment to 

an acute shift in routine. Aviation, Space, and 

Environmental Medicine, .5.2 (Aug), 703-710. 

26 

Moore-Ede, M., Czeisler, C., & Richardson, G. (1983). 

Circadian timekeeping in health and disease. Part 

I. Basic properties of circadian pacemakers. NE]M, 

.2Q.2. (8), 469-476. 

Naitoh, P. (1992). Minimal sleep to maintain performance: The search for sleep quantum in sustained 

operations. In C. Stampi (Ed.), Why we nap: Evolution, chronobiology, and functions of polyphasic 

and ultrashort sleep (pp. 199-216). Boston: 

Burkhauser. 

Naitoh, P., Kelly, T., & Englund, C. (1990). Health 

effects of sleep deprivation. In A. Scott (Ed.), 

Occupational Medicine: State of the Art Reviews, 2 

(2): 209-237. Philadelphia, PA: Hanley & Belfus. 

Price, W. & Holley, D. (1990). Shiftwork and safety in 

aviation. InA. Scott (Ed.), OccupationalMedicine: 

State of the Art Reviews, 2 (2): 343-377. Philadelphia, PA: Hanley & Belfus. 

Richardson, G., Carskadon, M., Orau, E., & Dement, 

W. (1982). Circadian variation of sleep tendency 

in elderly and young adult subjects. Sleep, 2, s82-

s92. 

Saldivar, J., Hoffman, S., & Melton, C. (1977). Sleep in 

air traffic controllers (DOT /F AAJ AM-77-5). Washington, DC: Federal Aviation Administration, 

Office of Aviation Medicine. 

Schroeder, D., Rosa, R., & Witt, L. (1995). Efficts ofBvs. 1 0-hour work schedules on the performance/alertness of air traffic control specialists (DOT /F AAJ 

AM-95/in press). Washington, DC: Federal Aviation Administration, Office of Aviation Medicine. 

Scott, A. & LaDou, J. (1990). Shiftwork: Effects on 

sleep and health with recommendations for medical surveillance and screening. In A. Scott (Ed.), 

Occupational Medicine: State of the Art Reviews, 2 

(2): 273-299. Philadelphia, PA: Hanley & Belfus. 

Taub, J. & Berger, R. (1973). Performance and mood 

following variations in the length and timing of 

sleep. Psychophysiology, 10, 559-570. 

Taub, J. & Berger, R. (1976). The effects of changing 

the phase and duration of sleep. journal of Experimental Psychology: Human Perception and Performance, 2 (1), 30-41. 

Tepas, D. (1982). Work/sleep time schedules and performance. In W. Webb (Ed.), Biological rhythms, 

sleep, and performance, (pp. 175-204). Chichester, 

England: John Wiley & Sons. 
Toothaker, L. ( 1991). Multiple comparisons for researchers. Newbury Park: Sage Publications. 

Turek, F. (1986). Circadian principles and design of 

rotating shift work schedules. American journal of 

Physiology, ill, R636-638. 

U.S. Congress, Office ofTechnology Assessment. (1991). 

Biological rhythms: Implications for the worker 

(OTA-BA-63). Washington, DC: U.S. Government Printing Office. 

Webb, W. (1982). Sleep and biological rhythms. In W. 

Webb (Ed.), Biological rhythms, sleep, and performance (pp. 87-110). Chichester, England: John 

Wiley & Sons. 

27 

Shiftwork, Age, and Performance 

Webb, W., & Levy, C. (1982). Sleep deprivation and 

performance. Psychophysiology, 12 (3), 272-276. 

Wegmann & Klein. (198 5). Jet-lag and air crew scheduling. In S. Folkard & T. Monk (Eds.), Hours of 

work: Temporal factors in work scheduling(pp. 263-

276). New York: John Wiley & Sons Ltd. 

Weitzman, E., Moline, M., Czeisler, C., & Zimmerman, 

J. (1982). Chronobiologyofaging. Neurobiology of 

Aging, .2, 299-309. 

Weschler, D. (1955). Manual for the Weschler Adult 

Intelligence Scale. New York: The Psychological 

Corporation. 

Zachary, R. (1986). Shipley Institute of Living Scale 

Revised Manual Los Angeles: Western Psychological Services, 

"ku.s. GOVERNMENT PRIN11NG OmCE: 19M- "'-"7/00131