ArticlePDF AvailableLiterature Review

Sleep and exercise: A reciprocal issue?

Authors:
  • Rythm, San Francisco, CA
  • Université Paris Descartes - Sorbonne Paris Cité; APHP

Abstract and Figures

Sleep and exercise influence each other through complex, bilateral interactions that involve multiple physiological and psychological pathways. Physical activity is usually considered as beneficial in aiding sleep although this link may be subject to multiple moderating factors such as sex, age, fitness level, sleep quality and the characteristics of the exercise (intensity, duration, time of day, environment). It is therefore vital to improve knowledge in fundamental physiology in order to understand the benefits of exercise on the quantity and quality of sleep in healthy subjects and patients. Conversely, sleep disturbances could also impair a person’s cognitive performance or their capacity for exercise and increase the risk of exercise-induced injuries either during extreme and/or prolonged exercise or during team sports. This review aims to describe the reciprocal fundamental physiological effects linking sleep and exercise in order to improve the pertinent use of exercise in sleep medicine and prevent sleep disorders in sportsmen.
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CLINICAL REVIEW
Sleep and exercise: A reciprocal issue?
Mounir Chennaoui
a
,
b
,
**
, Pierrick J. Arnal
a
,
b
,
c
, Fabien Sauvet
a
,
b
, Damien L
eger
b
,
d
,
*
a
Institut de recherche biom
edicale des arm
ees (IRBA), Br
etigny-sur-Orge, France
b
Universit
e Paris Descartes, Equipe d'accueil VIgilance FAtigue SOMmeil (VIFASOM) EA 7330, France
c
Laboratoire de Physiologie de l'Exercice, Universit
e de Lyon, Saint Etienne, France
d
Universit
e Paris Descartes, Sorbonne Paris Cit
e, APHP, H^
otel Dieu, Centre du Sommeil et de la Vigilance, Paris, France
article info
Article history:
Received 24 February 2014
Received in revised form
17 June 2014
Accepted 20 June 2014
Available online 30 June 2014
Keywords:
Exercise
Physical activity
Sleep
Sleep loss
Review
Insomnia
Obstructive sleep apnea
summary
Sleep and exercise inuence each other through complex, bilateral interactions that involve multiple
physiological and psychological pathways. Physical activity is usually considered as benecial in aiding
sleep although this link may be subject to multiple moderating factors such as sex, age, tness level,
sleep quality and the characteristics of the exercise (intensity, duration, time of day, environment). It is
therefore vital to improve knowledge in fundamental physiology in order to understand the benets of
exercise on the quantity and quality of sleep in healthy subjects and patients.
Conversely, sleep disturbances could also impair a person's cognitive performance or their capacity for
exercise and increase the risk of exercise-induced injuries either during extreme and/or prolonged ex-
ercise or during team sports.
This review aims to describe the reciprocal fundamental physiological effects linking sleep and exer-
cise in order to improve the pertinent use of exercise in sleep medicine and prevent sleep disorders in
sportsmen.
©2014 Elsevier Ltd. All rights reserved.
Introduction
Over the last decade exercise has been extensively recom-
mended as a major factor for improved health in the general pop-
ulation, in the elderly and in many groups with chronic diseases
such as obesity, type 2 diabetes, cardiovascular diseases, depression
and even cancer [1,2]. Increasing exercise has been found benecial
for reducing weight, preventing pain, improving mood and
enhancing the quality of sleep in patients with insomnia [1,3e5].
Getting sufcient sleep has also been recommended as insuf-
cient sleep has been identied as an associated risk factor for major
public health concerns: obesity, type 2 diabetes, cardiovascular
diseases, depression and accidents [6e8]. Sleeping 7e8 h has sys-
tematically been found to be associated with lower risks of
morbidity and mortality.
However it is still difcult to understand exactly how exercise
impacts on sleep and vice versa. In particular, very frequent asso-
ciations have been found between sleep loss and exercise-induced
injuries [9,10] suggesting physiopathological interactions between
sleep and injuries. Conversely, good sleeping habits and moderate
physical activity could be mutually benecial [11e13] and trigger a
virtuous circle that improves tness, particularly in sleep disorders
patients.
The aim of this review is therefore: 1) to understand how ex-
ercise affects sleep physiology, via its impact on temperature, car-
diac and autonomic function and the endocrine and immune
systems; 2) to clarify how the duration of sleep affects exercise
(exploring the impact of sleep loss, sleep restriction ad sleep
extension); 3) to observe the reciprocal inuence between sleep
disorders (insomnia and sleep apnea) and exercise.
Effects of exercise on sleep physiology (Fig. 1)
Denitions
Physical activity, sport, exercise and physical tness are terms
that lead to confusion. The term physical activity describes any
form of movement that results in energy expenditure and in-
cludes all the activities in day-to-day living, whether professional,
*Corresponding author. Centre du sommeil et de la vigilance, H^
otel Dieu, APHP, 1
Place du parvis Notre-Dame, 75181, Paris Cedex 4, France. T
el.: þ33 01 42 34 82 43;
fax: þ33 01 42 34 82 27.
** Corresponding author. Institut de Recherche Biom
edicale des Arm
ees (IRBA),
Br
etigny-sur-Orge cedex, BP73, 91223, France. Tel.: þ33 (0) 1 42 34 89 70; fax: þ33
(0) 1 78 65 14 58.
E-mail addresses: mounir.chennaoui@irba.fr (M. Chennaoui), damien.leger@htd.
aphp.fr (D. L
eger).
Contents lists available at ScienceDirect
Sleep Medicine Reviews
journal homepage: www.elsevier.com/locate/smrv
http://dx.doi.org/10.1016/j.smrv.2014.06.008
1087-0792/©2014 Elsevier Ltd. All rights reserved.
Sleep Medicine Reviews 20 (2015) 59e72
domestic or leisure-time activities [14]. Contrary to sport, phys-
ical activity is not performed competitively. Exercise is a
component of physical activity; it is planned, structured and
dened by its frequency, intensity and duration. Physical tness is
the ability to perform physical activity. A recent recommendation
from the American College of Sports Medicine and the American
Heart Association regarding physical activity and public health in
adults advises that, in order to promote and maintain health,
moderate-intensity aerobic physical activity for a minimum of
30 min on ve days each week, or vigorous-intensity aerobic
physical activity for a minimum of 20 min on three days each
week should be carried out [15]. Schematically, moder-
ateeintensity activities are those in which the heart rate (HR) and
breathing are raised but where it is still possible to speak
comfortably; whereas vigorous-intensity activities are those in
which the heart rate is higher, breathing is heavier and conver-
sation is harder.
Effects of exercise on sleep architecture
The effects of exercise on sleep are modulated by factors such as
individual characteristics and exercise protocol. Individual character-
istics include sex, age, tness level, type of sleeper and body mass
index (BMI), whereas exercise protocol includes acute or regular,
aerobic or anaerobic, and different characteristics such as intensity,
duration, environment (indoor or outdoor, hot or cold environment)
and the time of day. These variables have contradictory effects on
sleep. Various studies of this topic have concentrated on good and
relatively young sleepers (<35 y) [1619]; the scientic literature on
the elderly and poor-sleepers using objective measurements (poly-
somnography) is poor [17,20]. It is important to k eep in mind a possi ble
ceiling and oor effect of exercise on sleep in good sleepers (i.e., little
room for improvement in sleep); subjects with sleep disorders would
have the greatest potential for improvement. Interestingly, several
studies have since focused on these groups [2,11,21,22].
Abbreviations
AHI apnea-hypopnea index
BDNF brain-derived neurotrophic factor
BMI body mass index
CPAP continuous positive air pressure
GH growth hormone
HR heart rate
HRV heart rate variability
ICSD-2 international classication of sleep disorders-2nd
edition
MAE moderate-intensity aerobic exercise
NO nitric oxide
NREM non-rapid eye movement
OSA obstructive sleep apnea syndrome
PSG polysomnography
PSQI Pittsburgh sleep quality index
REM rapid eye movement
RLS restless leg syndrome
SD sleep deprivation
SMD standardized mean difference
SNS sympathetic nervous system
SOL sleep onset latency
SWS slow wave sleep
TST total sleep time
VO
2
max maximal oxygen consumption
WASO wake after sleep onset
Fig. 1. Possible effects of acute or regular moderate intensity aerobic physical activity on sleep. ANS ¼autonomic nervous system, BDNF ¼brain-derived neurotrophic factor,
Circadian R. ¼circadian rhythm, GH ¼growth hormone, IR ¼insulin resistance, PGE
2
¼prostaglandin E
2
, SWS ¼slow wave sleep, Tco ¼body core temperature, TNF-
a
¼tumor
necrosis factor alpha, link, probable link, inhibits (red).(For interpretation of the references to colour in this gure legend, the reader is referred to the web
version of this article.)
M. Chennaoui et al. / Sleep Medicine Reviews 20 (2015) 59e7260
Acute exercise
More specically, two meta-analyses reported that the effects of
acute exercise on sleep architecture showed a small increase in
slow wave sleep (SWS) and rapid eye movement (REM) sleep la-
tency and a decrease in the amount of REM sleep [16,18]. The in-
uence of exercise on improving sleep onset latency (SOL) and
decreasing wake after sleep onset (WASO) was found positive when
the exercise took place 4e8 h before bedtime, and negative when
the exercise was performed more than 8 h or less than 4 h before
sleep [16,18,19]. However, the studies reporting these de-
teriorations after exercising in the evening may be biased by the
fact they were performed on sedentary women (mean V0
2
max:
32 ml kg min
1
)[23], or after an extreme race (30 or 43 km) [24].In
these studies, the stress induced by exercise was very important
and sleep was disturbed, probably by the stress. It has also been
found that exercising before bedtime may not necessarily disturb
sleep (evaluated by actigraphy or questionnaire) [25,26]. Further-
more, recent studies have reported that vigorous or moderate late-
night exercise in children and young good sleepers (2e3 h before
bedtime) did not affect the SOL or WASO but using objective pol-
ysomnographic (PSG) measurements was actually seen to improve
SOL [27,28].
In conclusion, these ndings seem well established and
contradict long-standing sleep hygienetips that advise not to
exercise close to bedtime. The National Sleep Foundation has
amended its sleep recommendations for good sleepers to
encourage exercise without any caveat as to time of day as long as
this is not at the expense of sleep duration. Furthermore, once the
working day is over, the evening is a moment when exercise can be
incorporated into the daily routine as a leisure activity.
Regular exercise
Regular exercise represents an interesting non-pharmacological
treatment for poor sleepers [29]. In Kubitz's meta-analysis, regular
exercise (called chronic) was commonly found to be associated with
increased SWS, total sleep time (TST) and decreased REM sleep, SOL
and WASO in good sleepers [16]. A study of fty-one adolescents(53%
female) over a 3-wk period, including 30 min of moderate-intensity
exercise every weekday morning conrms theseresults. It showed an
improvement of objective duration and sleep efciency, SOL was
decreased and REM sleep latency increased compared to the control
group (without exercise) [30]. Moreover, the adolescents reported an
enhancement of subjective sleep quality, mood, and concentration
during the day. Other recent studies reported longer TST, shorter
WASO and greater sleep efciency in adolescents with high physical
activity levels [31,32]. Over the past decade, a few studies have
investigated the effect of regular exercise in older populations and in
people with sleep complaints [33e35]. Indeed, in middle-aged and
older adults with sleep problems, pooled analyses indicate that ex-
ercise training has a moderate benecial effect on sleep quality, sleep
latency and medication usage [34,36,37]. However in the 23 behav-
ioral intervention trials for insomnia reviewed by these authors, just
three of them used objective measurements (e.g., PSG). Moreover, a
long training program is usually needed to observe any signicant
effect of exercise on an objective(e.g., PSG study) improvementin the
sleep quality of older adultswith sleep complaintswas observed after
a 12-month exercise program [34,36]. However a shorter period of
exercise training (i.e., 16 wk of moderate-intensity exercise) only
impacted on subjective sleep quality assessed by the Pittsburgh sleep
quality index (PSQI) and the global sleep score but not objective sleep
[38]. The doseeresponse effect of exercise training on the subjective
sleep quality of postmenopausal women has been conrmed
recently [39]. Naylor and Penev also recently observed a similar in-
crease in SWS with only daily social and physical (low intensity)
activity over 2 wk in a 65e92-y old group [35].
Basic research in animals may be helpful in understanding the
link between exercise and sleep. A period of 8-weeks of chronic
aerobic exercise performed at night onset (equivalent to the
morning for humans) in old rats signicantly decreased sleep
fragmentation (35%) and increased EEG delta power (0.5e4 Hz)
during non-rapid eye movement (NREM) sleep. The changes in
sleep persisted for 2 wk after the end of exercise, indicating the
enduring effects of exercise on the central nervous system [40].
Either way, more rigorous methodological studies need to be
conducted to better demonstrate the benecial effects of exercise
training on sleep patterns as previous studies have not always
controlled the indirect effects of factors such as light exposition,
changes of food intake, mood, the effects of antidepressants and
circadian rhythms. Moreover, because exercise leads to signicant
long-term improvements in body composition, basic metabolic
rate, cardiac function, glucose control, mood and immune function
[18,41], it is actually hard to discriminate the direct and indirect
pathways implicated in the exercise-induced changes to sleep.
Effects of exercise on body temperature during sleep
Many studies have reported a clear link between sleep and body
temperature [42,43]. Indeed, sleep could be promoted by a
decrease in body temperature (0.5e1
C) [44] whereas an increase
in body temperature (1.5e2.5
C) alters sleep onset [45,46]. This
decrease at the level of the brain, in particular the pre-optic area,
seems to trigger sleep [47]. So since exercise affects body temper-
ature both during the exercise and recovery, it has been suggested
than exercise could inuence sleep.
Exercise induces an increase in central, skin and cerebral tem-
perature, related to the intensity and duration of the exercise and
the climatic conditions (temperature, humidity) [48,49]. So when
the exercise ceases, the body temperature is raised [44] with the
same effects on sleep as passively changing the body temperature.
When subjects are acutely exposed to heat immediately before
sleep, decreases in total sleep time and SWS occur, being often
accompanied by synchronic (concomitant) diminution in REM
sleep [49] .
Conversely, immersion in warm water, inducing a rise in body
temperature of 1.5e2.5
C, decreased the SOL and enhanced the SWS
the following night [45,46].Horneetal.(1985)alsocomparedthe
effects of a running exercise in the hot condition (by wearing extra
clothes) and cold condition (via body cooling); only exercise in the
hot condition elicited increases in SWS [50]. Indeed, after the initial
passive or exercise-induced hyperthermia, the thermoregulatory
mechanism comes into play, decreasing the body temperature via a
peripheral heat dissipation mechanism corresponding to peripheral
vasodilation. This gradient between distal and proximal skin tem-
peratures seems to be essential for initiating sleep [51,52]. This rapid
decline in core body temperature following active or passive
heat exposure increases the likelihood of sleep onset and may
facilitate entry into the deeper stages of sleep [42,53].Moreover,
regular physical activity (1 h, three times per week), induces a more
regular decrease in body temperature and promotes sleep [53].
Effects of exercise on cardiac and autonomic function during sleep
Sleep is characterized by important changes in the circadian
rhythm of heart rate and blood pressure induced by declining
sympathetic and increasing parasympathetic activity during the
night, in particular during SWS [54]. As investigation of cardiac
function in humans is straightforward, many studies have assessed
the changes in autonomic nervous system activity non-invasively
by using heart rate variability (HRV) and HRV is frequently
applied to understand autonomic changes during different sleep
M. Chennaoui et al. / Sleep Medicine Reviews 20 (2015) 59e72 61
stages and the effect of insomnia, sleep disordered breathing dur-
ing sleep and the daytime (See for review [55]). Sleep disorders and
particularly sleep loss induces a well-known constant sympathetic
overactivity associated with heart rate, blood pressure and an
increased risk of cardiovascular and metabolic diseases [55e57].
During chronic insomnia, patients showed an increase in heart rate
and a decrease of HRV, before sleep onset and during stage-2 NREM
sleep, but compared to controls, showed no differences during
Stage-3 NREM sleep. These results are consistent with the hy-
pothesis that autonomic hyper-arousal is a major pathogenic
mechanism in primary insomnia [58]. During exercise, the sym-
pathetic nervous system (SNS) is widely stimulated [59]. Several
investigators have examined the changes in cardiac and autonomic
function immediately after a single bout of sub-maximal exercise
(15e180 min), characterized by an increase in heart rate caused by a
decrease in parasympathetic activity and an increase in sympa-
thetic activity [60,61]. These changes in sympathovagal balance
immediately post exercise gradually return to pre-exercise values
during the following 24 h [61]. A meta-analysis on the effects of
exercise on heart rate variability has reported that regular exercise
improves vagal modulation, with a resulting decrease in heart rate
[62]. Several studies have shown an increased heart rate during
sleep after daytime exercise [24,27,63,64]. Similarly, moderate and
heavy exercise (marathon) leads to decreased nocturnal global
HRV, indicative of a decrease in parasympathetic activity [63].
However, when exercise was taken very late in the day, other
studies observed either no change in HRV parameters during sleep
or only at the beginning of the night [65,66]. Thus, the elevated
heart rate during early sleep seen after exercise may be a result of a
non-signicant decrease in vagal activity and increased sympa-
thetic activity [27].
Conversely, a period of 2 mo of intensive training has been seen
to increase vagal activity and decrease sympathetic activity during
sleep in sedentary subjects [59]. This enhancement of vagal mod-
ulation after regular exercise is interesting as increased heart rate
variability is a predictor of reduced risk of future cardiovascular
events [67]. Overtraining (dened as excessive training with
insufcient recovery and chronic decrement of performance)
induced a contrary effect, i.e., a progressive decrease in para-
sympathetic activity and an increase in sympathetic activity during
sleep in sedentary or trained subjects [59,68] and reduced heart
rate variability was seen to predict poor sleep quality in a case-
controlled study of chronic fatigue syndrome [69].
Nevertheless, we failed to nd evidence that changes in HR and
autonomic activity could directly affect or improve sleep quality
and quantity. Burgess et al. [70] observed that cardiac sympathetic
activity did not signicantly change across NREM-REM cycles. Their
results also indicate that the effect on cardiac sympathetic activity
of the time spent asleep may be greater than the inuence of sleep
cycles. Recently, Myllamaki et al. [65] observed that neither
increased exercise intensity nor duration disturbed sleep quality
(actigraphic study) although signicant increases in HR and
changes in HRV were observed.
Effects of exercise on endocrine function during sleep
The main hormonal axes, which respond to exercise, are
the gonadal and somatotropic axes, the hypothal-
amoepituitaryeadrenal axis and the SNS axis. The metabolic and
hormonal changes during exercise are responsible for important
modications, both to some central neurotransmitters and some
immune functions.
During human sleep, the hypothalamoepituitaryeadrenal and
SNS axes are down-regulated with the decrease of plasma cortisol,
epinephrine and norepinephrine levels but at the same time there
is a marked increase in growth hormone (GH), prolactin, and
melatonin [71,72]. A rapid increase in plasma thyroid stimulating
hormone is observed in the early evening and at around the
beginning of sleep [73]. However at the end of sleep, there is a
decrease in thyroid stimulating hormone levels.
Nocturnal GH concentrations following daytime physical activ-
ity have been reported to increase [74,75], decrease [76,77] or
remain unchanged [75,76].
In the 1995 study by Kern et al. [75], the authors investigated the
hypothesis that long-duration exercise of moderate, but not low
intensity, during the day changes the typical temporal patterns of
GH and cortisol during subsequent nocturnal sleep in tri-athletes.
They observed that this exercise did not affect the nocturnal
plasma levels of GH or cortisol. However, when the night was
divided into two periods, the long-duration exercise of moderate
intensity induced a decrease in GH secretion and increased cortisol
secretion during the rst part of sleep, while in the second part of
sleep GH secretion was increased and the increase in cortisol
secretion was lower.
More recently Tuckow et al., 2006 [78], investigated the ef-
fects of a daytime exercise bout on subsequent overnight GH
secretion. They demonstrated that despite the modication in
secretory dynamics, no change in 12-h mean or integrated GH
concentrations were noted in the control and exercise protocol
conditions. So although quantitatively similar total levels of GH
were secreted overnight in the two conditions, resistance exer-
cise modied the dynamics of secretion by attenuating burst
mass and amplitude but increasing burst frequency.
Exercise can also affect the levels of melatonin; however the
results are conicting due to indirect effects (light exposure, time of
day, intensity of exercise, gender and age) [79,80] and have an in-
direct effect on sleep.
Effects of exercise on metabolic functions during sleep
In the last forty years, there has been great interest in the role of
sleep on metabolic and endocrine function in the relationship be-
tween sleep loss, obesity and diabetes [81,82]. Yet as Uchida et al.
pointed out in their 2012 review, no data are available for the ef-
fects of exercise on metabolic functions during sleep [83].
However, growth hormone and cortisol are two hormones that
have an impact on glucose regulation. The effect of exercise on GH
and cortisol secretion can induce increased glucose utilization
during the REM phase of sleep and increased glucose levels in the
evening with reduced insulin sensitivity [84]. More research needs
to be done on the effects of exercise on metabolic functions during
sleep.
Effects of exercise on the immune-inammation response during
sleep
Sleep and the circadian system inuence the immune functions
[80,85] and there is increasing evidence to suggest bi-directional
communication between sleep and the immune system. In-
vestigations of the normal sleepewake cycle indicates that immune
parameters (numbers of undifferentiated naive T cells) and the
production of pro-inammatory cytokines (interleukin-6, tumor
necrosis factor alpha, interleukin-12) increase during early
nocturnal sleep whereas immune cells (natural killer cells) and the
production of anti-inammatory cytokines (interleukin-10) in-
crease during daytime.
Because sleep loss induces elevated levels of cortisol, decreased
testosterone and growth hormone levels [83], these results could
explain the potential protective effect of exercise in sleep deprived
subjects. Nevertheless, a new study must be conducted in order to
M. Chennaoui et al. / Sleep Medicine Reviews 20 (2015) 59e7262
conrm this hypothesis. And new research needs to be done on the
anti-inammatory effects of physical training on immuno-
inammatory responses induced by sleep deprivation (SD) and/or
sleep restriction.
Effects of exercise on mood during the night
In addition to physiological changes, it is well known that ex-
ercise also improves mood state [86e88], which can also be an
important additional factor in improving sleep. Moreover, sleep
disorders are associated with an increased risk of anxiety and the
development of depression [89]. Physical training is signicantly
associated with a decrease in anxiety and its physiological in-
dicators and can reduce the prevalence of depression and improve
the mental health of large populations [90]. Moreover, regular ex-
ercise decreases REM sleep which has a signicant anti-depressant
effect over time [91]. The anti-depressant effects of exercise have
recently been well studied, and the improved mood results from
elevated levels of brain-derived neurotrophic factor (BDNF) which
is directly attributable to exercise and so indirectly, to improved
sleep quality [83,86,87,90]. Such pathway relationships between
the acute and chronic effects of exercise and alterations in sleep
should be examined in future studies.
To conclude this part, we have shown that many interdependent
pathways may explain the impact of exercise on sleep quality.
Further research is required to explain how exercise impacts on the
quantity of sleep and how these pathways interact to modify SWS
and REM sleep.
Effects of sleep on exercise
Introduction
Improving the sleep quality of sportsmen and high-level ath-
letes is important, because it is vital for high levels of mental and
physical performance, general well-being and the recovery process
but also for the prevention of exercise-induced diseases [92e95].
Athletes do not usually benet from optimal sleep conditions and
are exposed to circadian disruption (jet lag during international
events), sleep habit changes (hotel, two players per room ),
stress and muscular pain due to intense night time exercises as
explained previously. Moreover, sleep loss could also alter exercise
activity in non-trained subjects and patients via many direct (fa-
tigue, sleepiness) and indirect effects (mood, vigilance ) (see
Fig. 2).
Effects of acute sleep loss on exercise performance
It is consensually admitted that sleep loss may have substantial
psychological effects. However, the impact of sleep loss on exercise
performance appears to us both inconclusive and unconvincing.
Exercise performance depends on physiological, psychological and
biomechanical parameters and the impact of sleep deprivation on
these is poorly understood at the moment.
Regarding maximal oxygen consumption (VO
2
max), a deter-
mining factor in aerobic effort, some authors have shown SD to be
associated with a decrease in VO
2
max [96e98], others did not nd
any change of VO
2
max associated with SD [99e102]. Similarly,
oxygen consumption during constant-load efforts seems not to be
inuenced by SD [97,103e105], while exercise performance during
constant-load efforts was decreased in the SD condition
[102e104 ,106] . Some authors have explained the impact of SD on
exercise as an enhanced perception of the exertion during exercise
known to decrease sub maximal performance [107e109]. These
psychological changes during exercise and the many adverse effects
of SD on cognitive performance such as increased lapsing, cognitive
slowing, memory impairment, a decrease in vigilance and sus-
tained attention, shifts in optimum response capabilities [110] or
dysfunctional emotional regulation [111] may inuence physical
performance especially during sports.
Fig. 2. Possible effects of acute or chronic sleep deprivation/sleep loss on physical performance, muscle recovery and exercise-induced diseases. ANS ¼autonomic nervous system,
BDNF ¼brain-derived neurotrophic factor, BP ¼blood pressure, Circadian R. ¼circadian rhythm, IR ¼insulin resistance, GH ¼growth hormone, HR ¼heart rate,
PGE
2¼
¼prostaglandin E
2
, RPE ¼rating of perceived exertion, TNF-
a
¼tumor necrosis factor alpha, link, probable link.
M. Chennaoui et al. / Sleep Medicine Reviews 20 (2015) 59e72 63
Based on scarce literature it appears that in both males and fe-
males, SD (one night) is not associated with any change in anaer-
obic performance [112] nor in the contributions of the anaerobic
energy systems to high-intensity exercise [101,112]. Maximal
strength loss was not observed during either isometric or isokinetic
contractions of upper or lower limbs during 60 h of continuous
wakefulness [105,113]. However, other studies observed a modest
decrease in functional performance of the upper and lower limbs
after a complex combination of sleep loss and exercise or after
prolonged SD (36e100 h of wakefulness) [114e117]. Moreover SD
seems to reduce the difference between morning and afternoon
performance assessed with anaerobic power variables [114,118].
It is also hypothesized that acute SD may affect exercise via
immuno-inammatory changes. In particular it was observed that
sleep restriction increased pro-inammatory cytokine, GH, and
testosterone concentrations after physical exercise (brief sprints)
but did not affect cortisol responses [119]; nor did a 30-h period of
SD alter leukocyte trafcking, neutrophil degranulation or secre-
tory immunoglobulin A responses either at rest or after sub-
maximal and strenuous exercise [120]. However, an increase in
insulin resistance and a decrease in glucose tolerance, both asso-
ciated with SD (although partially reversed by physical activity)
[121] were also seen as contributing to exhaustion.
Effects of chronic sleep restriction and sleep quality on exercise
performance
Short sleep is very prevalent among industrial populations and
may affect up to 30% of young adults [122]. However there is, to our
knowledge, no literature devoted to the association between
chronic sleep restriction and the level of physical exercise in
healthy subjects and little is known about the effects of chronic
sleep restriction (sleep debt) on exercise and performance.
Similarly, the role of sleep quality on exercise is still an unex-
plored eld of research. We have found only one study in a 14,148
sample of United State Army active, reserve, and National Guard
members (83.4% male), in which sleep quality was assessed from
two questions validated by the PSQI (0e6). Poor sleepers (5e6)
were signicantly (P<.001) more likely than good sleepers (0e1)
to meet aerobic exercise and resistance training recommendations,
and pass their army physical tness test in the last quartile [123].
Effects of sleep loss on exercise-related injuries
Some studies indicate that chronic or acute sleep loss is directly
correlated to athletic injuries [121,122]. Other authors dened a
specic disease called fatigue-related injuries, related to sleeping
6 h the night before the injury and stated that this reduced
amount of sleep is a direct, independent risk factor for injuries
during exercise [9]. In particular, sleep deprivation increases the
risk of over-strain injuries to the locomotor system [123] that could
be linked to the decrease of proprioception and postural control
[124,125] and reaction time [104] observed after acute sleep loss.
Recent sleep loss also impairs the functional recovery of muscles
following injury. Specically, 8 h of sleep deprivation acutely down
regulated activity of the protein synthesis pathway that repairs
muscle damage and triggered contractile function decits during
recovery [95,124]. These ndings highlight the role of sleep in the
regeneration of damaged muscle tissue. Resistance exercise could
be a non-pharmacological strategy to minimize or reverse sleep
deprivation-induced muscle damage [92].
Moreover, athletes practicing contact sports who experienced
concussions during the previous year reported more symptoms of
sleep disturbance and poorer sleep quality than did the controls
[125] and subjects with a low sleep quantity the night before the
concussion reported both a greater number greater number of
symptoms and more severe symptoms after the concussion [126].
Sleep restriction is a potent contributor to the development of so-
matic symptoms, particularly in males associating both sleep
deprivation and exercise [10] who reported increased pain sensi-
tivity [127]. In particular, sleep problems are associated with an
increased risk of chronic pain in the lower back, neck and shoulders
[13]. Nevertheless, regular exercise and maintenance of normal
body weight may reduce the adverse effects of mild sleep problems
on the risk of chronic pain [13]. Taken together, these results sug-
gest the creation of a pernicious circle including sleep loss, injuries,
decreased recovery patterns, an increased pain that themselves
favor sleep disturbances.
Sleep disturbances are also associated with overtraining during
periods of high volume training [94,128,129]. Moreover reduced
sleep quality can be associated with higher prevalence of upper
respiratory tract infections in overreaching populations [130].
The physiopathological pathways implicated probably associate
elevated levels of cortisol and inammation and the decreased
levels of testosterone and growth hormone observed during acute
and chronic sleep loss, that may interfere with tissue repair and
growth [124,127,131,132].
Moreover, some epidemiological and laboratory studies have
suggested that SD could decrease the tolerance to exercise in
extreme weather (i.e., heat or cold) [133e138]. So, sleep needs to be
preserved before and during exposition to environmental thermal
constraints. This question is of importance for subjects who do
outdoor sports with their inherent environmental constraints and
those who take part in long trail competitions with their additional
sleep deprivation constraints [133].
Indeed, among United States high school athletes, heat illness is
the third leading cause of death and SD has been identied as one
of the risk factors for heat illness and exercise-induced injuries
[134]. In particular, SD has been observed in more than 20% of cases
of passive heat stroke [135,136]. SD is also considered as a predis-
posing factor for heat acclimation inability [137] or exertional
heatstroke [134,135]. Landis et al. [137] interestingly observed that
one night of total SD (24e33 h of wakefulness) alters thermoreg-
ulatory responses. This response is characterized by 1) the atten-
uation of peripheral vasodilatation during passive or active heat
exposure [137e139] and 2) a lower sweat rate during moderate
intensity exercise [139,140]. The impact of SD was rather strong,
even in trained athletes as it has been observed that 28 h of
wakefulness were sufcient to alter the benet of 10 d of exercise-
heat acclimation [141]. Conversely, Moore et al. [142] observed that
three nights of partial SD (i.e., 2 h of sleep per night) did not alter
thermal strain, whole-body sweat rates or performance during
exercise in the heat.
The mechanisms that link SD to environmental diseases are not
well known and require further study. Adaptation to environmental
stress or exercise-induced heat exposure requires intact vaso-
motricity and sweat gland activity [143]. In particular, during heat
exposure, a decrease in heat-induced vasodilatation, a well-known
nitric oxide (NO)-dependent endothelial mechanism, leads to
decreased tolerance to heat and caloric dissipation through the skin
[144]. Many studies have described that, in healthy subjects, an
alteration of endothelial NO production occurred after only one
[145] or three nights of sleep restriction [146] or after 29 h of
continuous wakefulness [56]. This dysfunction could be related to
an increase in sympathetic vasoconstrictor activity [147] and/or
localized endothelial dysfunction [148] induced by a low-grade
inammatory response to sleep deprivation [56,131], that could
persist after two nights of recovery [132]. It has been demonstrated
that low-grade inammation, as observed after upper respiratory
or gastrointestinal illness, is sufcient to decrease endothelial-
M. Chennaoui et al. / Sleep Medicine Reviews 20 (2015) 59e7264
dependent vasodilatation and tolerance to heat [135] via an alter-
ation of the bio-availability of endothelial-NO [149].
Other authors have suggested that acute sleep loss is also a risk
factor for cold injuries (i.e., hypothermia and freezing of the ex-
tremities) [150]. Recent work has demonstrated that 29 h of
wakefulness alters local response to cold [151] characterized by
lower skin temperatures and cutaneous blood ow during cold
exposure and recovery. These changes are considered as risk factors
for local cold injuries (frostbite) and decreased dexterity during
cold exposure [152]. These potential effects of sleep loss need to be
taken into account when physical activity is carried out in the cold,
in particular for sports needing high dexterity (biathlon, moun-
taineering ). The mechanisms involved are probably a combina-
tion of increased sympathetic activity and alterations to endothelial
NO availability [153] both implicated in cold-induced vasodilation
[153], a frostbite and dexterity protective mechanism.
Protective effects of exercise before and during sleep deprivation
To date, only a few studies have evaluated the extent to which
exercise modies performance in the SD condition and most of
these have regarded exercise as an additional stress factor
[154,155]. In particular, it has been shown that, in humans, short
bouts of exercise may improve the sleepiness and fatigue associ-
ated with SD. However, acute exercise is not likely to prevent per-
formance decrements [154]. Similarly, the effect of eight, intense
cycling sessions (15 min at 20 km/h against a load of 2.5 kg) during
48 h of continuous wakefulness was seen to be associated with an
improvement in complex addition tasks, short-term memory and
auditory vigilance [155].
More recently, it was observed in rodents that regular physical
exercise improves many aspects of brain function and could even
induce neuroprotection. Indeed, 4 wk of physical training has been
shown to prevent the impairment of long-term memory associated
with sleep deprivation (24-h continuous wakefulness or 96-h REM
sleep deprivation) [156,157]. One possible explanation advanced by
the authors was that alterations of synaptic plasticity in the hippo-
campus (CA1 area) [157] and the dentate gyrus [158] were blocked,
probably via a decreased level of BDNF [156,158] and an increase in
the protein phosphatase calcineurin [158] and oxidative stress [159].
Sleep extension
Recent research has investigated how physical performance
may be improved using sleep extension. Mah et al. [12] studied the
impact of extended sleep over 5e7 wk on physical performance in
young basketball players. Extended sleep contributes to improved
athletic performance especially in shooting percentage and sprint
times. Cognitive performance (reaction time), mood, fatigue, and
vigor were also improved with increased TST. However, even if
subjects were well-trained before beginning the study, these re-
sults need to be conrmed with traditional controls. Moreover, one
week of sleep extension (10 h in bed per day) improved resilience
during subsequent sleep restrictions and facilitated task acquisition
during recovery, demonstrating that nightly sleep duration exerts
long-term (days, weeks) effects [160]. The extent to which sleep
restriction, measured objectively, impaired alertness and perfor-
mance and the rate at which these impairments were subsequently
reversed by recovery sleep, varies as a function of the amount of
nightly sleep obtained prior to the sleep restriction period. This
suggests that the physiological mechanism(s) underlying chronic
sleep debt may undergo long-term (days/weeks) accommodative/
adaptive changes [161]. Crediting a sleep bankmay be an pro-
tective countermeasure to subsequent sleep deprivation. Thus
behavioral interventions designed to increase sleep duration may
be an effective strategy in the treatment of various pathologies
[162,163].
Clinical issues
Exercise and insomnia
Insomnia affects one adult in four in most countries [164] and
10% of these are severely affected. Insomnia is consensually dened
based on the criteria of the DSM-IV [165] or the international
classication of sleep disorders-2nd edition (ICSD-2) [166]. Due to
its high prevalence and to the possible emotional impact of per-
formance and competition on sleep, it is understandable that
insomnia may affect exercise and performance. Conversely exercise
has been proposed as a way to improve sleep in subjects with
insomnia. Baron et al. [11] demonstrated that sleep inuences next-
day aerobic exercise rather than exercise inuencing sleep. The
relationship between TST and next-day exercise was stronger for
those with shorter TST at baseline. These results suggest that
improving sleep may encourage exercise participation. There are
two sides to this issue that will be discussed in more detail.
Does insomnia affect exercise?
Even if a large consensus exists regarding the fact that its day-
time impact is a major issue in the denition of insomnia
[165e167], the nature and the magnitude of this impact are still
controversial. Some studies have underlined objective impairments
in subjects with primary insomnia: a high level of cortisol [168] and
a higher heart rate variability [169]. However, these objective data
do not suggest a clear link between insomnia and fatigue, irrita-
bility or a decrease in daytime functioning. In a review on insomnia
and daytime functioning, Riedel and Lichstein [170] proposed that
the paucity of objective ndings in the literature may be due to the
fact that a) attempts at objective verication have focused on var-
iables that are unimpaired rather than areas of actual impairment,
or that b) methodological problems, such as between-subject
variability, have hidden actual differences between insomniacs
and persons without insomnia. Daytime sleepiness has received
the most attention, but it is becoming clear that a large number of
insomniacs are not sleepy during the day [89,170] except when they
have other sleep disorders (such as sleep apnea) or associated
sedative treatments [171]. Using a multiple sleep latency test
Bonnet and Arand [89] demonstrated that insomniacs were even
more alert than good sleepers during daytime.
Consequences of insomnia: relevance for athletic performance
There is no doubt that the question of the impact of insomnia on
athletic performance is a crucial issue. Competition is considered by
many athletes as stressful enough to impact their sleep the night
before an event and they may worry about the inuence of poor
sleep on their performance. There are few studies devoted to the
impact of insomnia on performance in athletes [172]. Performance
is a mix of physical and cognitive excellence and the question is to
understand how insomnia may affect both aspects. Travel and jet-
lag are also disrupting sleep and are frequently experienced by
athletes before a competition [173]. The jet-lag disorder is a circa-
dian rhythm sleep disorder that occurs as a consequence of rapid
travel through multiple time zones. The traveler may experience
excessive sleepiness, fatigue, insomnia, irritability, dysphoric mood,
gastrointestinal disturbance, or other symptoms after arrival at the
destination. Jet lag symptoms arise from the desynchronization
between the body's circadian rhythm, which is synchronous with
the location of departure, and the new sleep/wake cycle required at
the destination. The body clock desynchronization may affect sleep
quality, quantity, sleepiness and performance which appear to be
M. Chennaoui et al. / Sleep Medicine Reviews 20 (2015) 59e72 65
very sensitive to a global synchronization of physiological circadian
variables such as internal temperature, cortisol levels and cardiac
and respiratory rhythms which are all synchronized by the clock
[174]. It is therefore in the interest of the individual athlete and
team to understand the effects of jet lag and the potential adap-
tation strategies that can be adopted such as light, chronobiotics
(e.g., melatonin), exercise, and diet and meal timing [175].
Regarding the impact of insomnia on the physical performance
of athletes, several mechanisms may be involved. Insomnia may be
associated with SD and it is well documented in this review that
sleep decit has consequences on several physical factors for per-
formance in young athletes [103,109]. Insomnia may also be asso-
ciated with increased sleep fragmentation, which may also impact
negatively on daytime activity, as has been shown in shift workers
[176,177]. However we have no knowledge of specic data
regarding the performance of athletes with insomnia. Alongside
physical performance, it is easy to understand that attention, con-
centration and memory can also have a major impact in some
sporting competitions and that insomnia may alter these cognitive
factors of excellence in performance. However it is still unclear
exactly how insomnia impacts on next-day cognitive performance.
In a recent review examining neurobehavioral impairments in
primary insomnia and attempting to identify which cognitive do-
mains were most consistently impaired in this group, the authors
found that it was attention tasks, which have a high cognitive load,
and working memory tasks that showed performance decits in
insomnia patients [178].
Insomnia may also result from the competition itself. Increased
internal temperatures due to high intensity exercise, muscular pain
and increased emotions may contribute to disturbed sleep which
may have implications for subsequent exercise training.
The interaction between insomnia, mood and anxiety has been
extensively described [179] and is very relevant, even in young
adults and college students [180]. Insomnia may be an early
symptom of depression and anxiety, which may themselves affect
performance. Conversely insomnia is a risk factor in the develop-
ment of stress, anxiety and depression [179].
Finally drug treatments for insomnia may also affect alertness
the following day and therefore impact on an athlete's perfor-
mance. Again there is little literature either on the prevalence of
athletes taking hypnotics or on the effects of hypnotics on perfor-
mance. In a questionnaire survey completed by 1459 high school
student athletes in the east of France, 4% stated that they had used
doping agents at least once in their life (their main source of supply
being peers and health professionals). Thirty-four percent of the
sample smoked some tobacco, 66% used alcohol, 19% cannabis, 4%
ecstasy, 10% tranquillizers, 9% hypnotics [181].
One study compared cognitive function using the critical icker
fusion test in athletes treated with zolpidem versus placebo [182].
They estimated that the effect of zolpidem was only hypnotic and
did not disturb psychomotor and physical performance on the
following day in healthy adults. They then suggested that Zolpidem
could be used in healthy athletes to adjust their extrinsic sleep
disturbances and the resulting psychomotor and physical impair-
ments. This was also found with both zolpidem and zaleplon in a
survey of 12 healthy male trekkers who used these treatments to
improve their sleep, but who demonstrated no alteration in per-
formance or acute mountain sickness at 3613 m altitude [183].Ina
review devoted to the effects of melatonin in sport medicine [175],
the authors estimated that melatonin could be useful for treating
some sleeping disorders, even though the interactions between
sleep, melatonin and exercise had not been studied extensively
with trained study participants. It is unknown whether melatonin
plays a role in some exercise training-related problems such as
amenorrhea and over-training syndrome.
Does exercise inuence insomnia?
Alongside cognitive behavioral therapy, exercise is commonly
recommended as a treatment for insomnia. How exercise may
affect sleep has already been discussed, but we will look here at the
literature studying exercise and insomnia from an epidemiological
and clinical point of view.
There has been to our knowledge only one study (by Merrill
et al.) to look at the epidemiological effects on insomnia of an
intensive lifestyle modication program. The program associated
sport and stress management, 10 h per week over 4 wk in 2624
adults with insomnia [184]. Insomnia was decreased by 64% in the
group. Those who failed to lower their coffee/tea use after four
weeks were signicantly more likely to have a sleep disorder and be
highly emotive. Other studies have concentrated on sleep disorders
in general rather than insomnia, using the PSQI. Yang et al. recently
reviewed the effects of exercise training on sleep quality in middle-
aged and older adults with sleep problems [36]. From six studies
involving 305 participants (241 females) and an average training
duration of 10e16 wk they found that the participants with an
exercise program had a better global PSQI score, with a standard-
ized mean difference (SMD) of 0.47 (95% CI 0.08e0.86) than did the
control group. The exercise group also had signicantly reduced
sleep latency (SMD 0.58, 95% CI 0.08e1.08), and medication use
(SMD 0.44, 95% CI 0.14e0.74). However, the groups did not differ
signicantly in sleep duration, sleep efciency, sleep disturbance,
or daytime functioning.
Clinically, we found relatively few studies devoted specically to
exercise and insomnia. Guilleminault et al. used 22 patients with
insomnia to test the effects of moderate-intensity aerobic exercise
(MAE) associated with sleep hygiene therapy on their sleep, eval-
uated by a sleep log and actigraphy. After four weeks of the
regimen, they observed a non-signicant trend towards an
increased total sleep time and a reduced total wake time [185].
Passos et al. tested the effects of three different modalities of acute
physical exercise, assessed by polysomnography, on the sleep of 48
patients with chronic primary insomnia [5]. The patients were
assigned to four groups: control, MAE, high-intensity aerobic ex-
ercise, and moderate-intensity resistance exercise. Signicant
changes in sleep were only observed in the MAE group, with a 55%
reduction in sleep onset latency, a 30% reduction in total wake time,
as well as an increase in total sleep time (18%) and sleep efciency
(13%). This MAE program incorporated the following exercises:
shoulder press, chest press, vertical traction, leg press, leg curl, leg
extension, abdominal crunch, and lower back exercise. Three sets of
10 repetitions at 50% of one-repetition maximum were performed,
interspersed with 90-s recovery intervals. The exercise session time
was approximately 50 min. Passos et al. [22] also investigated the
effects of long-term (6 mo) moderate aerobic exercise on insomnia,
in a smaller group of subjects, using polysomnography. They found
a signicant decrease in sleep onset latency (from 17.1 to 8.7 min)
and wake time after sleep onset (from 63.2 to 40.1 min), and a
signicant increase in sleep efciency (from 79.8 to 87.2%)
following exercise. These effects did not vary between morning and
late-afternoon exercise. Sleep quality after aerobic exercise was also
assessed in 17 sedentary adults aged 55 y with insomnia, using
the PSQI [186]. Patients were randomized into two groups: 16 wk of
aerobic physical activity plus sleep hygiene compared to non-
physical activity plus sleep hygiene. The physical activity group
improved in sleep quality on the global PSQI, sleep latency, sleep
duration, daytime dysfunction, and sleep efciency PSQI sub-scores
compared to the control group.
However the intake of many other sedative antihistaminic or
benzodiazepine hypnotic drugs may be associated to side effects
such as daytime sleepiness in the morning, confusion, nausea,
muscle weakness [162,163]. The prescription of hypnotics in
M. Chennaoui et al. / Sleep Medicine Reviews 20 (2015) 59e7266
athletes has therefore to be limited and if possible not proposed for
the rst time at the eve of competitions.
Exercise and sleep apnea
Sleep apnea affects from 5 to 10% of adults. Males, and those
who are overweight or obese are more frequently and severely
affected [187]. Sleep apnea is consensually dened based on the
criteria of the ICSD-2, which lists non-restorative sleep, sleepiness
and intermittent hypoxemia as crucial signs of the disease; this
may potentially impact on exercise. Reciprocally it is not at the
moment obvious that exercise may have an impact on the sleep
apnea symptomatology. However, as it is well recognized that
exercise has a powerful impact on weight loss and that weight loss
improves sleep apnea [188], it is therefore not easy to clarify the
relationship between sleep apnea and exercise independently of
weight.
Does sleep apnea affect exercise?
It is widely recognized that sleep apnea does in fact limits ex-
ercise due to several associated factors.
From a cardiovascular point of view, obstructive sleep apnea
syndrome (OSA) is commonly associated with specic exercise
response characteristics, like exaggerated blood pressure [21,189]
or delayed heart rate recovery [190,191]. Recently Mansukhani
et al. carefully examined the link between OSA severity and exer-
cise testing outcomes independently of BMI and other cardiopul-
monary risk factors in a sample of 1204 patients [190]. They
concluded that patients with severe OSA (apnea-hypopnea index,
AHI 30) had a signicantly lower functional aerobic capacity and
heart rate recovery, and a higher post exercise blood pressure than
those without OSA (AHI <5) after accounting for confounding fac-
tors (all p<0.05). They concluded that OSA severity was associated
with reduced functional aerobic capacity and increased post-
exercise blood pressure independently of other confounding
variables.
Sleepiness may be one explanation for reduced physical activity
in patients with OSA. From a behavioral point of view, sleepiness
reduces the need and the time for physical activity. In a survey of 40
patients with obstructive OSA aiming to clarify their exercise ca-
pacities and their possible relationships with other ndings, a
battery of aerobic and anaerobic exercise tests was performed in
these patients and 40 control subjects [191]. They showed that the
apnea-hypopnea index was a signicant independent predictor of
aerobic capacity after controlling for a variety of potential con-
founders including BMI. They also suggested that the lower aerobic
exercise capacity of patients with OSA might be due to daily
physical activity that is restricted by the OSA itself. Sleepiness also
reduced the hypertensive response to exercise [21]. However the
lack of exercise itself seems to be predictive of the degree of
sleepiness in OSA. In an important survey of 1106 consecutive pa-
tients (741 men and 365 women) referred to a sleep clinic for OSA,
daytime sleepiness was assessed with the Epworth sleepiness scale
and activity evaluated with a quantiable physical activity ques-
tionnaire [192]. Linear regression analysis of the total sample after
adjusting for age, BMI, sex, central nervous system medication, and
diabetes showed that AHI, depression, and lack of regular exercise
were signicant predictors of sleepiness. Predictors of mild or
moderate sleepiness for both sexes were depression and AHI,
whereas predictors of severe sleepiness for men were lack of reg-
ular exercise, depression and minimum saturation of oxygen and
for women, AHI.
It is also clearly possible that the reduced observed VO
2
peak
observed in sleep apnea may explain the reduced activity and fa-
tigue [189,191]. Understanding how continuous positive air
pressure (CPAP) may improve physical exercise in patients treated
for OSA may clarify the relation between sleep apnea, fatigue and
exercise. Alonso-Fernandez et al. found nasal CPAP reversed the
depressed cardiovascular response to exercise in their study of 30
patients with OSA before and after CPAP versus sham CPAP (con-
trol) and 15 healthy subjects [193]. CPAP therapy was associated
with highly signicant improvements in all the indices of left
ventricular systolic performance response during exercise, whereas
with sham CPAP, all of them remained unchanged. CPAP also
allowed an increase in walking distance in 12 subjects with OSA
recovering from heart failure [194]. It was observed that during an
exercise test, CPAP increased the distance covered (538 ±78 m
versus 479 ±83 m) when compared to placebo. Ackel d'Elia et al.
found nasal CPAP plus exercise to be more efcient for reducing
sleepiness in 32 males with OSA than CPAP alone [195]. They
showed that a 2-mo exercise program associated with CPAP
treatment has a positive impact on subjective daytime sleepiness,
quality of life (physical functioning and general health perception),
and mood state (tension and fatigue) in OSA patients. It is generally
acknowledged that OSA causes inammation, with elevated levels
of C-reactive protein and tumor necrosis factor alpha and
interleukin-6 which are associated with sleepiness and fatigue
[196]. Physical exercise and CPAP improves inammatory proles
and possibly excessive daytime sleepiness due to its improvement
of inammatory proles.
Does exercise impact on sleep apnea?
Here also the relationship with obesity, cardiovascular function,
inammatory state and sleepiness makes it difcult to understand
how exercise may play a role in preventing or improving sleep
apnea syndrome. However several recent studies have insisted on
the benecial impact of exercise on sleep apnea. It seems that
combining both exercise and weight loss with CPAP may provide
the most effective treatment for many patients with OSA.
In an epidemiological setting, Awad et al. recorded the exercise
habits of 1521 adults of the Wisconsin sleep cohort between 1998
and 2000 [197]. The study demonstrated that exercise was associ-
ated with a reduced incidence of sleep-disordered breathing.
Controlling for BMI did not explain all the exercise-sleep disordered
breathing associations and there remained a non-signicant trend
in reduced incidence of sleep disordered breathing. This nding
suggests that exercise may also affect sleep-disordered breathing
via pathways other than weight loss.
From a clinical point of view, two recent studies have shown
that exercise may improve the severity of OSA by up to 50% of the
AHI, independently of the effect of weight loss [198,199], but this
improvement in AHI is not always found to be signicant [200].
Kline et al. showed in 42 subjects a signicant independent weight
loss effect of chronic exercise on AHI. They observedthat while only
25% of individuals who completed the exercise-training program
experienced treatment success (i.e., post-intervention AHI <20 and
reduction 50%), 63% experienced an AHI reduction 20%. Thus,
when evaluated as a stand-alone treatment for OSA, the efcacy of
exercise training seems to be lower than with CPAP or multilevel
surgery, but similar to other surgical treatments and approximately
equivalent to a 10% reduction in body weight. The mechanisms of
action remain unclear. Exercise clearly decreases sleepiness and
improves daytime functioning in patients with OSA. Kline et al.
observed this in 43 sedentary adults with OSA randomized to 12 wk
of moderate-intensity aerobic and resistance exercise training or a
low-intensity stretching control treatment [199]. Sleepiness and
functional impairment due to sleepiness were also improved, in the
exercise versus control groups, to a similar degree in terms of effect
sizes (d>0.5), though these changes were not signicant. More
work has certainly to be done on inammatory pathways in order
M. Chennaoui et al. / Sleep Medicine Reviews 20 (2015) 59e72 67
to better identify how exercise improves OSA independently of
weight reduction.
Along with insomnia and OSA, other sleep disorders such as
restless leg syndrome (RLS) or hypersomnia may also have conse-
quences on sleep and consequently on athletic performance. RLS is
dened according to the ICSD-2 as [165] an urge to move the limbs
that is usually associated with paresthesias or dysesthesias [201]
symptoms that start or become worse with rest [202] and who's
symptoms are at least partially relieved by physical activity, and
[202] who's symptoms worsen in the evening or at night. RLS
frequently also has a primary motor symptom that is characterized
by the occurrence of periodic leg movements during sleep. To our
knowledge only one short letter has been published, stating that in
Brazil 13% of 61 marathon runners had RLS compared to a preva-
lence of 7% in the general population [201]. Several studies have
shown that aerobic exercise is efcient in improving RLS in patients
with uremic RLS [202,203].
What exercise to recommend to sleep-disorder patients?
As described previously, exercise has been recommended as a
non-pharmacological treatment for insomnia [5,22,36,184,185] or
sleep-disordered breathing [197]. However, physical activity needs
to be progressive in patients suffering from sleep disorders, starting
at low intensity and preceded by a physical/cardiovascular check-
up. Indeed, growing epidemiological evidence indicates that short
duration sleepers and those with sleep disorders are at greater risk
of sudden cardiac death [204], coronary heart disease, myocardial
infarction, angina, stroke [205] or diabetes [206].
Every heart disease is a risk factor for exercise-induced acute
cardiac events, during the exercise itself or the immediate recovery
period [207], so we need to be cautious when recommending acute
intense exercise to subjects with sleep disorders.
Indeed, short periods of sleep due to restriction or deprivation
are a sufcient stress to induce increased blood pressure [208],
increased coronary vascular tonus [209], coronary calcications
[210], increased sympathetic activity [211,212], systemic inam-
mation (interleukin-6, e-selectin) [211,212] and endothelial
dysfunction [213,214]. Moreover, Sekine [145] et al. showed in
healthy subjects that just one night of sleep restriction (50%)
resulted in a decrease of coronary ow velocity reserve, a sign of
coronary endothelial dysfunction. An alteration of endothelial
function has also been described after three nights of sleep re-
striction in nurses [146] or just one night of total sleep deprivation
[56] in healthy subjects.
Endothelial dysfunction, an early predictive indicator of car-
diovascular disease, is characterized by a decrease in endothelial-
dependent NO production [215], which plays a protective role for
the vascular bed, preventing the abnormal coronary artery vaso-
constriction that leads to heart stroke [216]. Endothelial dysfunc-
tion is thus directly associated with exercise-induced myocardial
ischemia [217]. Indeed, the increased myocardial metabolic de-
mand and tachycardia [217] is only observed during exercise with
the respect of an intact endothelial-dependent vasodilatation
mechanism.
So, we can hypothesize that patients suffering from sleep dis-
orders are probably at risk for exercise-induced myocardial
ischemia or coronary heart failure and acute coronary events. We
therefore emphasize the importance of cardiologic medical
screening before starting a physical activity program with subjects
with poor sleep or sleep disorders [218]. Moreover, physical exer-
cise must be progressive and initially moderate, in order to improve
endothelial function [219] and decrease the risk of death [220].
Indeed, aerobic exercise appears to be more benecial than resis-
tance exercise for improving endothelial function [221]. Moderate
aerobic exercise training is considered as sufcient to decrease
oxidative stress, inammation, insulin resistance and to prevent
the risk of heart attack in patients with coronary spastic angina
[222]. Based on the study by Kemi et al. in rats, which showed that
moderate and high exercise training have the same benecial effect
on endothelial function [223] we strongly recommend moderate
aerobic exercise training in subjects suffering from sleep disorders.
Conclusion
Sleep and exercise inuence each other through complex,
reciprocal interactions including multiple physiological and psy-
chological pathways. Following practical recommendations, mod-
erate aerobic exercise training could be prescribed as a pertinent
non-pharmacological treatment of sleep disorders. New funda-
mental research must be carried out to improve our knowledge of
the complex physiological effects and to understand the benetof
exercise in the promotion of sleep in both healthy subjects and
patients. Sleep is also often mismanaged in sportsmen, with pejo-
rative consequences on cognitive performance, effort perception
and exercise-induced diseases. Better understanding of the physi-
ological responses to sleep loss is needed to enhance physical
performance.
Practice points
1. Regular moderate-intensity aerobic exercise is recom-
mended in the treatment or the prevention of sleep
disorders.
2. Exercising before bedtime may not necessarily disturb
sleep in good sleepers.
3. Beneficial effects of regular exercise on sleep may be
explained by multiple pathways with the interaction of
circadian rhythm, metabolic, immune, thermoregula-
tory, vascular, mood and endocrine effects.
4. Except for its psychological patterns, the effects of sleep
loss on exercise performance appear inconclusive.
5. Sleep loss must be considered as a risk factor for
exercise-related injuries
6. Sleep quantity and quality must be studied in athletes
using easy and inexpensive methods such as a sleep
questionnaire, actigraphy or ambulatory
polysomnography.
Research agenda
In the future, we need to:
1. Assess more precisely how exercise impacts on meta-
bolic functions during sleep.
2. Have more standardized exercise protocols for pop-
ulations with sleep disorders, insomnia and sleep apnea
(with objective measurements).
3. Evaluate the effects of acute and intense exercise in
sleep-deprived subjects.
4. Understand the anti-inflammatory effects of physical
training on immuno-inflammatory responses induced by
sleep deprivation and/or sleep restriction.
M. Chennaoui et al. / Sleep Medicine Reviews 20 (2015) 59e7268
Acknowledgments
Pierrick Arnal was supported by a doctoral research grant from
the General Directorate for Armament (DGA, ministry of defense).
The authors declare no conict of interest.
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