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Physical fitness and sleep

Griffin, SJ 1985 , 'Physical fitness and sleep', PhD thesis, University of Tasmania.

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Physically fit athletes have been found to have
elevated slow wave sleep (SWS) , longer sleep duration and
decreased sleep onset latency (SOL) compared with unfit
sedentary individuals. It has been hypothesized that the
critical variable in these effects is the subject's level
of fitness resulting from habitual exercise. Certain
negative findings, however, cast doubt on this interpretation.
The aim of the current series of experiments was to further
investigate the effects of physical fitness on electroencephalographic
(EEG) and hormonal aspects of sleep. These
investigations are of theoretical interest as they potentially
provide information regarding the functional significance
of sleep and SWS in particular. Those theories which hypothesize
a relationship between peripheral metabolism and
sleep, for example, the restorative and energy conservation
theories, would predict that chronic physical exercise would
promote SWS and sleep-related anabolic hormones. In contrast,
those theories which do not propose a direct relationship
between peripheral metabolism and sleep, for example, the
cerebral restitution and immobilization theories, would
predict no effect of physical fitness on sleep.
By using independent group designs, previous
studies have potentially confounded aerobic fitness with
other characteristics of athletic individuals. Therefore,
the first experiment in this thesis assessed the sleep of
proficient athletes on two occasions; initially when they
were unfit and subsequently when aerobically fit. In
addition, the sleep of athletes was compared with that of an unfit, non-athletic, sedentary group. The athletes
tended to sleep longer and had elevated SWS and non-rapid
eye-movement (NREM) sleep compared with non-athletes.
These differences were independent of the aerobic fitness
of the athletes. Thus, it was concluded that aerobic
fitness was not a critical factor but, rather, had been
confounded with a more enduring variable associated with
physical fitness.
A secondary issue addressed in Experiment 1 was
the relationship of daytime exercise, physical fitness and
SWS. It has been hypothesized that a facilitative effect
on SWS of a single exercise session is dependent on the
subjects being physically fit. This hypothesis was tested
by assessing the effect of exercise on sleep in the athletes
when they were unfit and subsequently when they were fit.
The hypothesis was not supported as no effect of exercise
on sleep was observed. It is possible, however, that fitness
may increase the probability of an exercise effect occurring
when one or more other conditions are met.
Experiments investigating the effects of physical
fitness on sleep have typically concentrated on EEG variables.
A number of factors have also suggested that hormonal aspects
of sleep may be influenced by physical fitness. Experiment 2,
therefore, was designed to examine the effect of physical
fitness on the night-time secretion of human growth hormone
(hGH), prolactin and cortisol. In addition, the relationship
between the secretion of these hormones during the night and
body composition was assessed. Two groups of 17 subjects, one of fit athletes and
the other of unfit non-athletes, were selected so that the
groups were matched for weight, height, lean body mass (LBM)
and fat levels. Subjects slept in a sleep laboratory for
3 non-consecutive nights; an adaptation night and two
experimental nights. On one experimental night blood samples
were collected, while on the other, baseline sleep was
assessed and the catheter was not inserted. Weight and height
were measured and LBM assessed by 24hr urinary creatinine.
The effect of physical fitness was tested by a comparison
of the two groups, while the effect of body composition was
assessed by correlation analyses.
Physical fitness did not have a significant effect
on either sleep or hormone levels, though in the latter case
the results were marginal and are worthy of further investigation.
Body composition was related to hGH level,
percentage LBM being positively correlated with hGH levels.
These results were significant for all subjects combined
and for the fit group, though not the unfit group alone.
Consistent with the findings of Experiment 1, it was
concluded that physical fitness is not a critical factor
influencing sleep variables and that previous studies may
have confounded it with other variables.
Since body composition is related to physical
training it was hypothesized that differences in SWS
observed between athletes and non-athletes may be related
to differences in body composition. This hypothesis was
tested by comparing sleep and anthropometric variables of fit athletes and unfit non-athletes. Two sets of data
were analysed. One from the Hobart laboratory included
subjects from Experiment 1 plus others run in other
experiments at that time (designated Experiment 3a) , while
the other consisted of the subjects from Experiment 2
(designated Experiment 3b). Twenty-five fit and 22 unfit
subjects were run in Experiment 3a and 17 fit and 17 unfit
in Experiment 3b. LBM and fat were estimated using a
different method in each experiment. The results showed
percentage LBM was negatively correlated to SWS in fit
subjects while the amount of LBM and weight were negatively
related in the unfit groups. When all subjects were
combined within each experiment, significant negative
correlations were found between SWS and both LBM and
percentage LBM in Experiment 3b. The results, therefore
supported the hypothesis that body composition influences
SWS levels.
Different types of physical training develop
different anthropometric characteristics and other physiological
attributes. Thus, it was considered possible that
different types of training would influence sleep. This
hypothesis was tested in Experiment 4. The sleep of four
groups of 10 young male subjects who differed with respect
to the type of athletic training in which they habitually
engaged~was compared on two consecutive, non-exercise nights.
The groups were : aerobically trained endurance runners,
power trained weight lifters and bodybuilders; athletes with
mixed anaerobic, aerobic and power training; and an unfit,
non-athletic, sedentary, control group. Pre-planned comparisons showed that the control
group did not differ from the combi~ed athletic groups on
any sleep variable. However, the aerobic group had more
SWS and NREM sleep, slept longer and had shorter SOLs than
the power group. The mixed group was intermediate on each
of these variables. The data show that the type of physical
training in which athletes engage has substantial effects of
their sleep. It was not possible to determine from
Experiments 3a, 3b and 4 if the effects of type of training
and body composition are related. The results, however,
demonstrate that variations in peripheral physiological
factors are related to sleep architecture; particularly to
The results of the experiments reported in this
thesis clearly show that aerobic fitness has no direct
effect on the sleep variables assessed. They do, however,
indicate that peripheral factors associated with physical
training are related to aspects of sleep architecture. The
results also have implications for theories of sleep. While
sleep may serve cerebral restitution and immobilization
functions it also appears to be influenced by peripheral
factors and thus the findings are inconsistent with present
formulations of the cerebral restitution and immobilization
theories of sleep. However, despite finding peripheral
effects on sleep, the data were not consistent with a
general restorative view as the direction of the results
was largely incompatible with this theory. Finally, in relation to the energy conservation theory of
sleep as applied within species or within individuals,
the data indicate that athletes as a broad group do not
use the elevation of SWS or TST to compensate for high
energy expenditure. A subgroup of athletes (endurance
athletes), however, may use this method to balance their
energy intake and expenditure.

Item Type: Thesis - PhD
Authors/Creators:Griffin, SJ
Keywords: Sleep, Physical fitness
Copyright Holders: The Author
Copyright Information:

Copyright 1985 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1985.

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