Sleep, 18(1):30--38
© 1995 American Sleep Disorders Association and Sleep Research Society
Sleep Deprivation: Effects on
Work Capacity, Self-Paced Walking,
Contractile Properties and Perceived Exertion
*c. D.
Rodgers, tD. H. Paterson, t:j:D. A. Cunningham, tEo G. Noble, tF. P. Pettigrew,
§W. S. Myles and t:j:A. W. Taylor
*School of Physical and Health Education, University of Toronto,
Toronto, Ontario, Canada;
tFaculty of Kinesiology and +.Department of Physiology, The University of Western Ontario,
London, Ontario, Canada; and
§Defense and Civil Institute of Environmental Medicine
Toronto, Ontario, Canada
Summary: The primary purpose of this study was to examine the effect of a 48-hour period of sleep deprivation
on the performance of selected physical work tasks [30-45% of maximum oxygen consumption (V0 2 max)]. In
addition, this study assessed the effect of continual performance of physical work during sleep deprivation on
standardized physiological and psychological test scores. Nineteen male subjects performed six different physical
tasks, designed to involve all major muscle groups, during a 48-hour period of sleep deprivation. Fourteen subjects
served as sleep-deprivation controls. Performance on all physical work tasks decreased significantly. Neither sleep
deprivation (SD) or sleep deprivation in conjunction with continuous physical work (SDW) had any effect on muscle
contractile properties, anaerobic power measures or resting blood glucose and lactate concentrations. Only SD
subjects demonstrated a decline in cardiorespiratory function. Self-selected walking pace decreased and perceived
exertion increased significantly in the SDW group. Positive and negative mood scores were adversely affected in
both groups, the total change being greatest in SD subjects. The results indicate that performance of physical work
tasks requiring 30-45% V0 2 max declines significantly over a 48-hour period of sleep deprivation. However, maximal
physiological function is not unduly compromised by either the work tasks in conjunction with sleep deprivation
or by sleep deprivation alone. Key Words: Sleep deprivation-Work capacity-Muscle contraction-Self-paced
walking-Perceived exertion-Mood-Physicallabor.
Previous studies that have examined the effect of sleep
deprivation on functional task performance have focused
primarily on cognitive tasks or tasks demanding a high
degree of visual effort (1). In instances where the effects
of sleep deprivation on the ability to sustain physical
tasks have been examined, the results are dependent upon
the nature of the "tasks" evaluated and the duration of
the sleep-deprived period. Most often the physical tasks
have been either a series of physiological measurement
tests (2), interspersed low-intensity [25-30% maximum
oxygen consumption (V02max)] treadmill exercise periods (3,4), or military performance tasks, the intensity
of which has not been well documented (5). To date,
Accepted for publication August 1994.
Address correspondence and reprint requests to Dr. C. D. Rodgers,
School of Physical and Health Education, The University ofToronto, 320 Huron Street, Toronto, Ontario M5S IAI Canada.
30
there are no studies that have examined the effect of 48
hours of sleep deprivation on the performance of physical
work tasks requiring an intensity of work effort equivalent to 35-40% V0 2max. This intensity is important in
that it has been shown to be equivalent to the self-paced
intensity of industrial workers over an 8-hour work day
(6,7). Furthermore, it is believed to represent an intensity
of effort that is able to be sustained up to 24 hours (8).
However, no studies exist that have ascertained whether
or not this functional level of activity can be maintained
under sleep-deprived conditions. Hence, the first objective of this study was to examine the effects of sleep
deprivation on performance of physical tasks requiring
a work effort equivalent to 35-40% V0 2max.
A secondary objective of this study was to examine
the effect of sleep deprivation on physical work task
performance in conjunction with regular evaluation of
physiological function on standardized tests. In a study
31
SLEEP DEPRIVATION AND WORK CAPACITY
by Haslam (5) both military exercises and performance
on various physical fitness tests during sleep deprivation were examined. However, the physical fitness
tests utilized were not clearly discussed, and it is difficult to determine the effects of sleep deprivation on
both the functional tasks and physiological parameters.
This type of evaluation has particular implications for
situations such as military operations, which might
require continuous physical effort in a sleep-deprived
state as well as under the threat of potential emergency
efforts. If performance of maximal physiological function is unduly compromised, the consequences are of
major significance.
METHODS
SO subjects read or watched television in a lounge. In
addition, every 2 hours SD subjects went for a short
(less than 100 m) walk. The only interruptions to either
groups' activities were meals, which were served approximately every 6 hours (at least 2 hours before testing), and repeated physiological assessment of some
parameters at 12, 36 and 48 hours. A supervisor was
assigned to each group at all times to ensure continued
wakefulness of the subjects. Total kilocalories consumed (C = 8, 158 ± 1,150; E = 8,237 ± 1,283) across
2 days and the percentage of proteins (15 ± 3%), carbohydrates (50 ± 7%) and fat (35 ± 6%) distributed
across the diet (six meals and two snacks) did not differ
between the groups. Subjects were not allowed to consume any caffeine-containing substances, alcohol or
drugs during the experimental period.
Subjects
Thirty-three male volunteers were randomly subdivided into two groups: sleep deprived + work tasks
(SOW: n = 19; 23.0 ± 3.2 years; 76.5 ± 7.6 kg) and
sleep deprived only (SD: n = 14; 22.6 ± 2.0 years;
77.6 ± 8.9 kg). During a 48-hour period of sleep deprivation subjects in the SDW group performed a continuous series of work tasks, whereas SO subjects read
or watched TV. Both groups were tested on a variety
of physiological parameters prior to, during, and upon
completion of the 48-hour experimental period. All
testing procedures conformed to, and the subjects were
made aware of, the Declaration of Helsinki statement
for the testing of human subjects.
Testing procedures
Phase I-familiarization
One week prior to the onset of the experimental
period, subjects in both groups were given a briefphysical examination and were familiarized with the Wingate test (9) and muscle contractile properties measurement protocol. The medical examination was done
to ensure that all subjects were in good health and
would not be unduly compromised by 48 hours of sleep
deprivation. Familiarization with the Wingate test and
contractile properties protocol was necessary to prevent contamination of the actual experimental data
due to lack of familiarity with the testing procedures.
Phase II -experimental period
General procedures. A 12-hour fasting blood sample
was drawn from each subject upon their arrival (7:00
a.m.) at the laboratory (Time 0). Subjects were then
assessed on a variety of physiological and psychological
parameters. Upon completion of this baseline test, the
SOW group began a repeated series of work tasks and
Physiological parameters - measurement techniques
The following series of assessment tests were administered to all subjects at the onset ofthe experiment
(Time 0) and upon completion of the 48-hour sleep
deprivation period. The self-paced walking test was
also repeated at 8 and 32 hours.
1. Blood glucose and lactate levels
Blood samples were drawn from the antecubital vein
and analyzed for plasma glucose and lactate levels on
a Model 23 L Lactate/Glucose Analyzer (Yellow Springs
Instruments). Hematocrit and hemoglobin levels were
determined using standard micromethods as described
by Bauer (10).
2. Muscle contractile properties
Contractile properties of the triceps surae group were
determined according to the methods of Klein et al.
(11) using an apparatus similar to that which has been
described previously by Davis and White (12). Briefly,
the subject's left knee and foot were placed in a steelbar restraining apparatus, the knee being held in place
by a metal plate connected to a strain gauge. A surface
electrode was placed over the belly of the gastrocnemius muscle for surface electrical stimulation of the
triceps surae muscle group. Muscle contractile properties were assessed at the level of twitch contraction,
and at 10- , 20- and 50-Hz contractions. The contractile force signal obtained from the strain gauge was
amplified and fed into a DEC A/D converter, digitalized and stored for later analysis. A measure of maximal voluntary contraction of the triceps surae group
was also obtained on each subject upon completion of
the contractile properties test.
Sleep, Vol. 18, No.1, 1995
32
C. D. RODGERS ET AL.
3. Anaerobic peak power and average power output
The Wingate test of anaerobic power (9) was used
to assess anaerobic peak power (over 5 seconds) and
average power output (over 30 seconds). This was done
by having the subject pedal all-out for 30 seconds
against a predetermined load setting [0.075 x body wt
(kg)] on a Monark bicycle ergometer. From the data
input of pedal revolutions per unit time and resistance,
values for total work, peak, mean and low-power outputs were calculated. A fatigue index was also calculated by subtracting the low-power output from the
high-power and dividing the resulting value by the
high-power output.
4. Submaximal work capacity
The PWC 170 test was administered to determine the
submaximal work capacity of each subject. Subjects
began pedaling (50-60 rpm) an electrically braked cycle
ergometer at 150 W. The workload was then increased
25 W every 2 minutes until a heart rate of 170 beats/
minute was achieved. At this time the test was terminated and the final workload attained recorded.
5. Self-paced walking
A self-paced walking test was administered to each
subject to evaluate the effect of sleep deprivation on
self-selected speeds of walking. The protocol selected
was a modification of the tests ofBassey et al. (13) and
Ekblom et al. (14) as has previously been described by
Cunningham et al. (15). Briefly, each subject was asked
to walk two lengths of an outdoor course of 30 m, in
response to each of the following pace instructions: a)
walk rather slowly (slow pace); b) walk at a normal
pace, neither fast nor slow (normal pace); and c) walk
rather fast but without overexerting yourself (fast pace).
For each of these self-selected paces, velocity and pace
frequency were determined. The measure of velocity
has been shown to be reliable and reproducible (15),
with a correlation coefficient of 0.81 and no significant
differences between repeated tests.
6. Perceived exertion test
To determine each subject's perception of work effort, two cycle ergometer protocols were administered.
The first, the response protocol (R), necessitated that
each subject pedal an electrically braked cycle ergometer (Collins Pedal mate) at 70 rpm for seven 45-second
exercise bouts at loads ranging from 100 to 180 W,
each separated by 15 seconds of rest. Immediately after
each work bout the subject was asked to rate their
perceived intensity of work effort according to the Borg
scale. For the production protocol (P) the subject once
again performed seven 45-second exercise bouts, sepSleep. Vol. 18. No.1. 1995
arated by 15 seconds of rest. However, in this instance
the subjects themselves were responsible for setting
appropriate work settings to yield an exercise intensity
corresponding to a Borg scale rating of either fairly
light (a rating of 11), somewhat hard (a rating of 13)
or hard (a rating of 15). The order of perceived intensity
for the seven workbouts was 13, 15, 11, 13, 11, 15 and
13. During both protocols subjects were prevented from
observing the control panel work-load reading. A rest
period of 1 minute was given between the two test
protocols. Test score was calculated by averaging either
the perceived rating (R protocol) or the exercise work
load (P protocol) of exercise bouts 2 through 6.
Psychological parameters - measurement techniques
At 0, 8, 32 and 48 hours, questionnaires were administered to the subjects to assess their mood and
level of fatigue (16). The mood scale contained 20
positive and nine negative words that could be used
to describe one's mood (e.g. alert, jittery, happy,
grouchy, etc.). Subjects were asked to score each word
using a Lichert scale (not at all-O points; a little-l
point; quite a bit-2 points; extremely-3 points). The
higher the score on the positive words, the more positive the mood of the subjects; the higher the score on
the negative words, the more negative the mood. For
the assessment of fatigue, subjects rated a series of 10
statements, ranging from "very lively" to "ready to
drop" on a better than (2 points), same as (1 point),
or worse than (0 points) scale. Scores were totaled with
low scores being indicative of a more fatigued state.
Work Tasks
Each subject in the SDW group performed the following series of six tasks approximately six times during the 48-hour sleep-deprivation period. The order of
tasks was randomized across subjects. Breaks were only
given between items to allow the subjects to walk to
the next work task station, for meals or for physiological/psychological testing (8, 12 and 32 hours). All tasks
were designed to provide demands similar to tasks of
military field operations.
The individual task protocols were as follows. Task
1: the number of sandbags carried over a distance of
5 meters in 30 minutes. Task 2: the distance walked
in 30 minutes with a 12-kg packsack. Task 3: the work
rate on a cycle ergometer was set at 80% of V0 2 max
(predicted from submaximal exercise) for a 2-minute
period. This task was repeated three times with a 10minute rest interval between each repeat. The measure
used was the completion of a set work load. Task 4:
the number of stakes planted in 45 minutes. Task 5
the number of revolutions of an arm ergometer wheel
33
SLEEP DEPRIVATION AND WORK CAPACITY
TABLE 1. Sleep-deprived work task performance
24-48 hours
0-24 hours
SDW work tasksa
18.5 ± 5.4*
Task I (n = 6): Sandbags carried/30 minutes
32.5 ± 11.1
1,260 ± 480 m *
1,830 ± 810 m
Task 2 (n = 9): Distance walked/30 minutes
Completed
Task 3: Completion-set bicycle work load
Completed
29.7 ± 14.5*
43.7±9.1
Task 4 (n = 7): Stakes planted/45 minutes
995 ± 96*
1,207 ± 138
Task 5 (n = 8): Arm ergometer revolutions/2 x 15 minutes
462.5 ± 136.2 m*
812.5 ± 277.5 m
Task (n = 9): Wheelbarrow loads x 15 m/30 minutes
Values are represented as means ± standard deviation.
a Variation in number of subjects completing different tasks is due to incomplete rotation of all subjects through all six tasks in each
time segment.
* Indicates a significant (p < 0.05) difference in performance between the first 24 hours and the last 24 hours.
(load equivalent to 40% of the subject's V0 2 max) that
could be generated in 15 minutes. Task 6: the number
of times a wheelbarrow was loaded with top soil and
pushed 15 m in a 30-minute period. Items were scored
by counting the number of tasks completed within the
defined time frame.
Statistics
Paired t tests were used to compare performance
scores on the work tasks. Scores on the psychological
and physiological performance tests were compared
using analysis of variance (time, group) and analysis
of covariance (self-paced walking test) techniques
(BMDP program #P2V). When indicated, post hoc between-group comparisons were assessed using the Bonferroni procedure (BMDP program #P7D).
perimental period. There was no significant effect of
work and/or sleep deprivation on measurements of
anaerobic power as determined by the Wingate test
(Table 4). A significant (p < 0.05) decrease in cycle
ergometer work rate at 170 beats/minute (PWC 170) was
noted only in the SD group (Table 4).
Figure 1 displays a synopsis of the percentage change
in each of the physiological parameters for the two
groups. Although there were no significant betweengroup differences, the SDW group did demonstrate a
greater negative (undesirable) change in all but two
(MVC; submaximal work capacity) of the 14 parameters assessed. The total percentage change across all
the physiological parameters (excluding blood parameters) was -38.78% (range -10.99 to 1.57%) in the
SD group and -48.6% (range -8.63 to -0.36%) in
the SDW group.
Physiological and psychological measurements of perception
RESULTS
Work tasks
Over the final 24 hours of sleep deprivation, performance scores on all but the cycle ergometer task
(task 3) decreased significantly (p < 0.05) (Table 1).
Physiological parameters
Forty-eight hours of sleep deprivation had no significant effect on blood glucose or blood lactate concentration (Table 2) in either the SD or SDW group.
Muscle contractile properties of the triceps surae group
(Table 3) remained relatively constant across all frequencies examined for both groups throughout the ex-
Although both SD and SDW showed a decrease in
self-selected walking pace at all speeds (slow, normal
and fast), after 48 hours of sleep deprivation this decline was only significant (p < 0.05) in the SDW group.
There was no significant difference between the two
groups in the number of steps necessary to cover the
30-meter distance (Table 5).
The ratings of an imposed work load (R protocol)
or the production of a work load corresponding to a
Borg scale rating (P protocol) did not change significantly after 48 hours of sleep deprivation in the SD
group. In contrast, SDW subjects showed a significant
(p < 0.05) increase in perception of work (R protocol)
TABLE 2. Resting blood glucose and lactate concentrations for sleep-deprived and sleep-deprived work task groups
SD group (n = 14)
Parameter
o hours
48 hours
4.30 ± 0.30
4.18 ± 0.48
Glucose nM/1
0.54 ± 0.29
0.58 ± 0.57
Lactate mM/1
Values are represented as means ± standard deviation.
SD = sleep deprived only; SDW = sleep deprived + work tasks.
SDW group (n
=
19)
o hours
48 hours
4.85 ± 1.00
0.65 ± 0.52
4.47 ± 0.32
0.42 ± 0.34
Sleep. Vol. 18, No.1. 1995
C. D. RODGERS ET AL.
34
TABLE 3. Contractile properties of the triceps surae for sleep-deprived and sleep-deprived work task groups
SD group (n
o hours
=
SDW group (n
14)
o hours
48 hours
=
19)
48 hours
8.9 ± 2.4
8.5
8.7 ± 3.0
8.5 ± 2.9
Pt (Newtons)
46.7 ± 13.1
44.1
42.6 ± 14.5
43.8 ± 15.7
Po 10 Hz (Newtons)
75.3 ± 20.9
70.3 ± 23.1
68.8
67.0 ± 21.6
Po 20 Hz (Newtons)
97.6 ± 29.6
92.3
91.9 ± 28.0
87.1 ± 26.8
Po 50 Hz (Newtons)
136.6 ± 25.9
128.1
137.1 ± 39.4
125.2 ± 34.3
MVC (Newtons)
Values are represented as means ± standard deviation.
Pt = twitch tension; Po = tension at Hz indicated; MVC = maximal voluntary contraction; SD = sleep deprived only;
deprived + work tasks.
and a significant (p < 0.05) decrease in performance
(P protocol) (Table 6).
As was to be expected, both groups demonstrated a
significant (p < 0.05) decrease (indicative of being more
fatigued) in their fatigue rating after 48 hours of sleep
deprivation (Table 6). SDW subjects demonstrated a
significant (p < 0.05) deterioration in their mood by
32 hours (Table 7). This was in contrast to SD subjects
who did not show a significant (p < 0.05) decline in
mood until 48 hours.
A summary of the percentage change in each of the
physiological/psychological measurements of perception is displayed in Fig. 2. The SDW group demonstrated a greater negative (undesirable) change in all
but one (negative psychological score) of the nine parameters assessed. Total percentage change across
measurements of perception was -426.3 in the SD
group (range - 281.3 to - 6.6) and - 396.0 in the SDW
group (range - 215 to - 7.7).
DISCUSSION
Of critical importance in this study was the finding
that performance on all work tasks decreased significantly after 48 hours of sleep deprivation. Moreover,
this decrease in performance occurred despite a continued ability to maintain performance on physiological test items reflecting functional capacity. This would
suggest that although sleep-deprived individuals may
have the physiological capacity to do the work, the
interference of mood, perception of effort or even the
± 2.5
±
±
±
±
13.5
20.9
26.5
22.2
SDW = sleep
repetitive nature of the tasks decreases the ability of
individuals to maintain a constant level of work output
in a sleep-deprived state. This speculation is further
supported by the decrease in performance in the SDW
condition only on all tasks involving the perception of
effort. The primary implication of these findings is that
continuous physical tasks at 35-40% V0 2 max are inhibited by 48 hours of sleep deprivation but maximal
efforts can still be achieved. Thus, in situations requiring an all-out effort, it appears that the necessary
level of physiological function could still be achieved.
The primary purpose of this study was to determine
the effect of a 48-hour period of sleep deprivation on
the performance of physical work tasks requiring a
work intensity of 35-40% V0 2 max. The observed decrement in physical work task performance suggests that
such tasks are unable to be continued at optimal levels
of performance during 48 hours of sleep deprivation.
This finding is particularly important because most
industrial environments require a self-paced effort of
this intensity over a typical work day (6,7). Although
Home and Pettitt (8) have indicated that this intensity
of effort can be sustained up to 24 hours, results from
the present study indicate that by 48 hours of continued
wakefulness significant performance declines occur.
Previous work by Haslam (5) found that 48-72 hours
of continued wakefulness is likely to render soldiers
militarily ineffective. Although the intensity of the work
effort by the soldiers in the Haslam study was not
documented, many of the tasks performed (shooting,
weapon-handling, digging, marching and patrolling)
TABLE 4. Peak power, mean power, fatigue index and PWC170 workrate for sleep-deprived and sleep-deprived + work task
groups
SD group (n
Parameter
Peak power output (W·kg-)
Mean power output (W·kg-')
Fatigue index (%)
PWC 170 (watts at 170 beats/minute)
o hours
=
14)
48 hours
SDW group (n = 19)
o hours
12.0 ± 1.8
11.7 ± 2.0
11.9±1.4
9.3 ± 0.9
9.5 ± 1.0
9.0 ± 1.6
44.5 ± 8.2
45.2 ± 7.8
40.3 ± 9.0
273 ± 41.0
243 ± 35.0*
276 ± 50
Values are represented as means ± standard deviation.
SD = sleep deprived only; SDW = sleep deprived + work tasks.
* Indicates a significant (p < 0.05) difference in performance after 48 hours of sleep deprivation.
Sleep, Vol. 18, No. I, 1995
48 hours
10.9
8.9
39.1
275
± 2.2
± 1.2
± 12.8
± 79
SLEEP DEPRIVATION AND WORK CAPACITY
35
TABLE 5. Self-paced walking speed andfrequency (30-m course) for sleep-deprived and sleep-deprived + work task groups
SD group (n
= 14)
= 19)
SDW group (n
o hours
48 hours
o hours
48 hours
Slow
Speed (m/second)
Frequency (steps/minute)
1.60 ± 0.58
118 ± 19
1.37 ± 0.47
111 ± 16
1.14 ± 0.24
96 ± 13
0.93 ± 0.18*
79 ± 11
Medium
Speed (m/second)
Frequency (steps/minute)
2.30 ± 0.77
145 ± 12
2.02 ± 0.66
136 ± 16
1.60 ± 0.35
108±8
1.31 ± 0.24*
96 ± 8
Fast
Speed (m/second)
Frequency (steps/minute)
3.13 ± 1.21
165 ± 8
2.66 ± 1.02
152 ± 9
2.14 ± 0.53
125 ± 8
1.78 ± 0.32*
113 ± 10
Pace
Parameter
Values are represented as means ± standard deviation.
SD = sleep deprived only; SDW = sleep deprived + work tasks.
* Indicates a significant (p < 0.05) difference in performance after 48 hours of sleep deprivation and physical activity.
were similar in nature to those used in the present
study. In contrast, other studies have demonstrated
that physical work can be maintained over similar or
longer periods of sleep deprivation. However, the intensity and/or duration of the physical work tasks assessed in these studies was lower than that required by
the subjects in the present study. This would suggest
that either the required work intensity of the tasks in
the present study was too high, or that the duration of
work time was too long.
A more frequent analysis of performance data, perhaps on l2-hour intervals, might have provided a
clearer picture of the duration over which this intensity
of effort can be maintained. Evaluation of task performance of both the SD and SDW groups at time 0
and at 48 hours might also have provided a clearer
picture of the role of self-pacing in continued task performance. The addition of a non-sleep-deprived control group would also help to isolate more clearly the
effects of the sleep-deprived condition from the potential confounding effects of the repetitive nature and/or
inherent boredom of the tasks on task performance.
It is interesting to note that the greatest decrements
in performance occurred in those tasks requiring significant involvement of both the upper and lower body.
The number of sandbags carried in 30 minutes and the
distance traveled with a loaded wheelbarrow showed
a mean loss of 55% and 40%, respectively, after 48
hours of sleep deprivation. In contrast, pedal rate on
the bicycle ergometer was maintained, whereas the
number of revolutions on the arm ergometer and the
distance walked during 30 minutes decreased by only
17% and 23%, respectively. This variation in response
would suggest that the exact nature of the task that is
to be performed over a prolonged period of time plays
a significant role in the degree of decrement experienced. Although physiological function (as reflected by
the lack of difference in the individual parameters measured in this study) was not unduly compromised, the
total percentage decline in physiological function experienced by the SDW subjects was greater than that
observed in the SD subjects. It is possible that the effect
of this combined total body decrement is, in part, reflected in the greater percentage change in the performance of these "total" body physical activities. However, the importance of the role of psychological factors
and the need for self-pacing in the observed task performance decrement can also not be overlooked.
The second objective of this study was to examine
the effect of the continuous performance of physical
work tasks on various psychological and physiological
parameters. It is quite common in military situations
to require maximal efforts after long-term periods of
sleep deprivation and physical work; however, the impact of this combined condition has received limited
attention.
In general, as assessed by the individual standardized tests, there was no significant effect of physical
work during sleep deprivation on physiological functional capacity. The SDW group did demonstrate,
however, a greater total decline in physiological capability over the 48-hour sleep-deprivation period. This
TABLE 6. Perceptual task scores for sleep-deprived and sleep-deprived + work task groups
SD group (n = 14)
Parameter
RPE response protocola
Workrate production (watts)
Fatigue ratings
o hours
9.9 ±
211 ±
13.1 ±
(n=
1.1
22
2.7
7)
SDW group (n
=
19)
48 hours
o hours
48 hours
10.6 ± 1.3
197 ± 31
6.0 ± 3.3*
(n = 7)
10.4 ± 0.8
197 ± 39
13.8 ± 2.8
11.2 ± 1.1*
175 ± 39*
5.3 ± 1.8*
(n = 11)
(n = 11)
Values are represented as means ± standard deviation.
SD = sleep deprived only; SDW = sleep deprived + work tasks; RPE = .
a Increase in score indicates more "difficult".
* Indicates a significant (p < 0.05) difference in performance after 48 hours of sleep deprivation.
Sleep. Vol. 18. No. I. 1995
C. D. RODGERS ET AL.
36
Perception Related Parameters
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Physiological Parameters
FIG. 1. Percentage change in performance on physiological tests
following 48 hours of sleep deprivation. MPO/kg bw = mean power
output (Wingate test); PPO/kg bw = peak power output (Wingate
test); PI = fatigue index (Wingate test); SMWC = submaximal work
capacity; Pt = twitch tension; PolO = tension at 10 Hz; Po20 =
tensio"n at 20 Hz; Po50 = tension at 50 Hz; MVC = maximal voluntary contraction.
FIG. 2. Percentage change in performance on perceptual and psychological tests following 48 hours of sleep deprivation. SPW-S =
self-paced walk: slow speed; SPW-N = self-paced walk: normal speed;
SPW-F = self-paced walk: fast speed; Positive = positive mood score
test; Negative = negative mood score test.
In the present study, both SD and SDW subjects showed
no significant decline in performance in either muscle
finding is similar to the work of others but expands contractile ability or anaerobic power output. Thus the
the physiological parameters examined to include mus- addition of physical work tasks during the sleep-decle contractile properties and self-paced walking ef- prived period indicated no further physiological impairment to the SDW subjects, and when maximal
forts.
Symons et al. (2) demonstrated that after 60 hours efforts were required, both groups could perform. An
of sleep deprivation neither anaerobic ability nor max- analysis of the low-frequency tetanic tension data does
imal isometric and isokinetic strength were impaired. suggest, however, that SDW subjects may have experienced a degree of low-frequency muscular fatigue as
TABLE 7• Mood scale ratings for sleep-deprived and sleep- a result of their physical task performance. Although
the decrease in tension for isometric tetanic contracdeprived + work task groups
tions obtained through electrical stimulation was not
Parameter
SD(n= 14)
SDW (n = IS)
statistically different between the two groups, the dePositive scalea
crease was twice as great in the SDW group. This type
o hours
37.3 ± 6.1
35.7 ± 7.8
of low-frequency fatigue following muscular contrac8 hours
35.3 ± 7.9
34.9 ± 6.3
tion has been demonstrated in several earlier studies
32 hours
30.1 ± 10.1
24.2 ± 8.0*
48 hours
23.0 ± 11.4*
19.7 ± 7.7*
(for review see reference 17) and, when taken in conjunction with a lack of change in anaerobic power outNegative scaleb
o hours
3.2 ± 3.3
4.0 ± 2.0
put, suggests that the high-threshold or fast-twitch mo8 hours
3.3 ± 3.1
4.3 ± 2.8
tor units were not fatigued by the added physical tasks,
32 hours
7.8 ± 4.9
11.4 ± 6.4*
whereas low-frequency (slow twitch) motor units did
48 hours
12.2 ± 5.8*
12.6 ± 3.9*
tend
to exhibit signs of early impairment. Such a specValues are represented as means ± standard deviation.
ulation might also explain the greater percentage decSD = sleep deprived only; SDW = sleep deprived + work tasks.
a Decrease in score = less positive mood.
rement observed in performance in those physical tasks
b Increase in score = more negative mood.
that
required a more "total body" effort.
* Indicates a significant (p < 0.05) difference in mood rating when
In the present study, the effect of sleep deprivation
compared to 0 hours.
Sleep, Vol. 18, No.1, 1995
37
SLEEP DEPRIVATION AND WORK CAPACITY
and sleep deprivation plus work on cardiorespiratory
function was examined by evaluating each subject's
work capacity at a heart rate of 170 beats/minute. It
was of interest to observe in this study that only the
SD subjects showed a loss of cardiorespiratory function
over the period of sleep loss, as demonstrated by their
decrease in work rate at this heart rate. SDW subjects
were able to maintain their initial level of work capacity, and thus their initial level of cardiorespiratory
performance. Previous studies have shown V0 2 max
to be unchanged (18-21) or to be decreased (3,22) following periods of sleep loss. The decline in V0 2 max
most often has been attributed to an increased plasma
volume and associated decrease in O 2 carrying capacity
of the blood (22,23) and/or to a decrease in the oxygen
cost of breathing (3). Recent work by Goodman et al.
(23) has extended the potential role of plasma volume
despite the conflicting V0 2 max data and has suggested
that the variable effects of sleep deprivation on cardiorespiratory performance may in fact reflect the conflicting influence of the positive features of enhanced
plasma volume, such as increased preload in conjunction with a decrease in blood viscosity, and the negative
features of a decrease in hemoglobin. In light of the
discrepancy in results observed in the present study
between the SDW and SD groups, it is possible that
performance of the physical work tasks by the SDW
subjects enabled the positive influences of enhanced
blood volume to outweigh the negative effects, thus
enabling a greater level of cardiorespiratory performance to be maintained.
The final group of parameters assessed in this study
were indices related to perception of effort and measures of mood and fatigue. Results of the self-paced
walking test, R protocol and P protocol indicated that
only the SDW group experienced a significant change
in their perception of work effort over the course of
the study. This would suggest that it is not the fatigue
elicited by sleep deprivation that accounts for this
change in perception, but, more likely, the fatigue associated with physical work in conjunction with sleep
deprivation. In a series of experiments using a combination ofRPE assessment over prolonged work bouts
(50 minutes) and somewhat similar Rand P protocols,
Myles (24) showed that the duration of the exercise
bout and the physical fatigue associated with the exercise bout are critical factors in determining whether
a change in RPE occurs. In short-duration activities
(30 seconds) sleep deprivation of 54 hours was found
to have no effect on RPE, whereas physical fatigue had
only a small effect. In contrast, for activities lasting
more than several minutes, RPE increases progressively as a function of both physical fatigue and sleep
loss. The present data would support an even greater
role of physical fatigue in altering the perception of
work effort in short-duration (45-second) activities. It
is likely that the difference between these two studies
is due to the extensive nature of the physical activity
performed during the sleep-deprived period.
To date, this is the first study to examine the effects
of sleep deprivation and physical work on self-paced
walking. The lack of change in self-paced walking speed
in the SD group in this study supports earlier findings
of Soule and Goldman (25), who failed to show any
change in self-paced treadmill walking with a 150-30kg backpack after 31 hours of sleep deprivation, despite
an increase in RPE. However, the significant change
in walking speed at all paces in the SDW group emphasizes once again the role of the performance of
physical tasks during the sleep-deprived period in altering the subject's perception of effort.
Although there was a more rapid decline in mood
in the SDW group, the overall percentage decline (positive + negative mood rating) was greatest in the SD
subjects (SD = 317; SDW = 262.8). This difference
appears to be primarily due to the greater increment
in the negative mood score in the SD subjects. Exercise
previously has been identified as a non-task-situation
factor that might enhance arousal during sleep deprivation (26). The present data suggest that exercise,
although not improving overall mood state, might serve
to offset negative mood changes.
In summary, the data from the present study indicate
that although the performance of physical work tasks
requiring an effort equivalent to 35-40% V0 2 max declines significantly over a 48-hour period of sleep deprivation, maximal physiological function is not unduly
compromised by either the work tasks in conjunction
with sleep deprivation or by sleep deprivation alone.
Individuals who do participate in physical activity while
sleep deprived are more likely to experience both a
significant change in their perceived effort to complete
certain tasks and a more rapid change in mood state.
The total percentage decline in mood state does appear,
however, to be offset by physical work task performance during the sleep-deprived period.
Acknowledgements: This research was supported by a
grant from the Defence and Civil Institute of Environmental
Medicine, Downsview, Ontario. The authors thank former
graduate students M. A. Babcock, P. M. MacPherson, K. M.
Roberts, C. L. Rice, M. M. Sopper and R. T. Thayer for their
valuable assistance in the data collection for this project.
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