Sleep and Biological Rhythms 2006; 4: 199– 206 doi:10.1111/j.1479-8425.2006.00234.x
© 2006 The Authors
Journal compilation © 2006 Japanese Society of Sleep Research 199
Blackwell Publishing AsiaMelbourne, AustraliaSBRSleep and Biological Rhythms1446-9235© 2006 The Authors; Journal compilation © 2006 Japanese Society of Sleep ResearchOctober 200643199206Review ArticleExercise and human circadian rhythmsY Yamanaka
Correspondence: Graduate student Yujiro Yamanaka,
Department of Physiology, Hokkaido University Graduate
School of Medicine, N-15, W-7, Kita-ku, Sapporo 060-8638,
Japan. Email: email@example.com
*Presented at the World Federation of Sleep Research and
Sleep Medicine Societies 2nd Interim Congress, New Delhi,
India, 22–26 September 2005.
Accepted for publication 17 May 2006.
Effects of physical exercise on human circadian rhythms*
Yujiro YAMANAKA, Ken-ichi HONMA, Satoko HASHIMOTO, Nana TAKASU, Toshihiko MIYAZAKI
and Sato HONMA
Department of Physiology, Hokkaido University Graduate School of Medicine, Sapporo, Japan
Bright light is the principal zeitgeber for the biological clock in mammals, including humans. But
there is a line of evidence that non-photic stimuli such as physical activity play an important role in
entrainment. Scheduled physical activity, such as wheel and forced treadmill running, has been
reported to phase-shift and entrain the circadian rhythm in rodent species. In humans, several stud-
ies have reported the phase-shifting effects of physical exercise. A single bout of physical exercise
at night was demonstrated to phase-delay the circadian rhythm in plasma melatonin. However, for
the entrainment of human circadian rhythm, a phase-advance shift is needed. Previously, we dem-
onstrated that scheduled physical exercise in the waking period facilitated the entrainment of
plasma melatonin rhythm to the sleep/wake schedule of 23 h 40 min. This result suggested that
timed physical exercise produced phase-advance shifts. A regular physical exercise also facilitated
entrainment of the circadian rhythms associated with acute phase-delay shifts of the sleep/wake
and light/dark schedule. These ﬁndings suggest that physical exercise is useful to adjust the cir-
cadian rhythm to external time cues, especially for totally blind people and elderly people.
Key words: circadian rhythm, entrainment, human, phase shift, physical exercise.
The performance as well as the effects of physical exer-
cise are known to depend on the time of day when the
exercise is performed.1,2 The biological clock is gener-
ally involved in such time-of-day effects, but the pre-
cise mechanisms for these particular issues are not
The circadian pacemaker, the central structure of the
biological clock, is located in the hypothalamic supra-
chiasmatic nucleus (SCN) in mammals and is entrained
by a light/dark cycle through the photic input from the
retina. The SCN consists of ca 8000 neurons on each
side and most of them show robust circadian oscillations
in neural activity with a period slightly different from
exactly 24 h.3,4
When healthy, sighted people are shielded from a 24-
h light/dark cycle without knowledge of the time of day,
their endogenous circadian rhythms such as plasma
melatonin and core body temperature free run with a
period that is not exactly 24 h. Therefore, to adjust to the
24 h local environmental time, our biological clock must
make a phase-advance shift by about 1 h every day. It has
been demonstrated that natural sunlight is the principal
zeitgeber for the human biological clock, and morning
bright light phase advances and evening bright light
phase delays the circadian clock (Fig. 1).5,6 However,
approximately half of blind people have been reported to
show normal entrainment of the circadian rhythm in
plasma melatonin, but the other half exhibited altered
or free-running rhythms.8 In addition, non-photic
Y Yamanaka et al.
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200 Journal compilation © 2006 Japanese Society of Sleep Research
stimuli such as a forced sleep/wake schedule has been
reported to synchronize the endogenous circadian
rhythms of totally blind individuals with a non-24 h
schedule while living in a constant condition of dim
light.9 This ﬁnding supports an idea that the non-photic
stimuli act as a time cue for the human biological clock.
Is physical exercise able to entrain the mammalian
biological clock? It is well known that physical activity,
such as wheel and forced treadmill running, phase shifts
and entrains the circadian rhythms in rodent species.
Several studies have assessed the effectiveness of phys-
ical exercise as a phase-resetting cue (non-photic zeit-
geber) in humans as well.10,11
PHYSICAL EXERCISE AND CIRCADIAN
RHYTHM IN NOCTURNAL RODENTS
Physical activity such as wheel running and forced
treadmill running phase-shifts the circadian rhythms in
nocturnal rodents.12–14 Brieﬂy, free-running rhythms
under constant dark or light in several rodent species
were phase shifted or entrained by the periodical induc-
tion of running wheels in a cage.15–21 In addition, the
period of free-running rhythms was shortened by access
to a running wheel.17,22,23 A complete phase response
curve (PRC) for a 3-h pulse of novelty-induced wheel
running was demonstrated in the Syrian hamster.15 The
PRC shows a prominent phase-advance portion in the
subjective day (rest phase) and small delay portion in
the late subjective night. These ﬁndings indicate that
physical exercise is able to entrain circadian rhythms
in nocturnal rodents. However, the critical variable for
clock resetting associated with wheel running remains
unknown. Possible explanations for clock resetting by
non-photic stimuli in rodent species have been
advanced. For example, physical activity affects the SCN
circadian pacemaker via the geniculo-hypothalamic
tract.24 Neurotransmitters such as neuropeptide-Y
(NPY) and serotonin have been proposed to mediate
non-photic effects of physical activity.25–27 Physical activ-
ity increases an arousal state, which may eventually feed
back though the NPY pathway from the intergeniculate
leaﬂet to the SCN, and/or through the serotonergic affer-
ents from the raphe nuclei.13,28
It has been suggested that the elevation in body tem-
perature may act as an input to the circadian pacemaker
of mammals, since temperature is a strong zeitgeber for
non-mammalian vertebrates and insects.
Physical activity increases core body temperature, the
level of which is circadian phase-dependent, and the
increment is larger in the rest phase than in active phase
in mammals including humans.29,30 In the PRC for 3-h
wheel running in the Syrian hamster,15 the maximum
phase-advance shift is observed during the middle of the
inactivity phase, which corresponds to the phase of tem-
perature trough and to the phase exhibiting the largest
increment of body temperature by 4-h wheel running.29
These results do not contradict the notion that physical
exercise phase-shifts the pacemaker by changing the
body temperature. On the other hand, injections of
the benzodiazepine, triazolam, induce phase shifts in
the circadian rhythm of hamsters by acutely increasing
their locomotor activity.31,32 The PRC for the triazolam
injection is similar to that for wheel-running31 but the
increase in body temperature is not the signal mediating
the phase-shifting effects of triazolam,32 because triaz-
olam increases body temperature in both restrained and
unrestrained animals but phase-shifts the circadian
rhythms only observed in unrestrained animals.32 Fur-
thermore, Mrosovsky and Biello (1994) suggested that it
is not running per se that is critical for phase shifting the
pacemaker but it may be the motivational context for
running.33 Therefore, at present, there is limited and
small evidence that a change in the body temperature is
the mediator of the phase shift induced by physical
Further studies are needed to fully understand the
mechanism of clock resetting by physical exercise in
rodents and the relation between photic and non-photic
Figure 1 A human phase response curve for bright light
which is measured under free-running conditions. The two
results5,6, represented by open and closed circles,
respectively, are combined (adapted from Beersma and Daan,
Circadian time of mid pulse (h)
(O: Honma & Honma, 1988 and : Minors et al., 1991)
Phase shift (h)
Exercise and human circadian rhythms
© 2006 The Authors
Journal compilation © 2006 Japanese Society of Sleep Research 201
EFFECTS OF PHYSICAL EXERCISE ON
HUMAN CIRCADIAN RHYTHMS
A single bout of physical exercise
In hamsters, increased physical activity by 3-h wheel-
running during the rest period is associated with phase-
advance shifts of the biological clock. Van Reeth et al.
(1994) examined whether or not physical exercise
induced phase-advance shifts in humans when carried
out in a usual rest period (nocturnal sleep time).10 In
this study, the circadian rhythms in plasma melatonin
were assessed twice under constant routine conditions,
once in the absence of physical exercise and once with
low intensity physical exercise of 3-h duration [40–60%
of peak oxygen uptake (VO2)]. The light condition was
constant dim light exposure (<300 lux). The phase
shifts were measured on the 1st day after physical exer-
cise. The timing of the physical exercise ranged from
−5 to +4 h around the trough of the core body temper-
ature rhythm. A single bout of exercise induced a robust
phase-delay shift. The result was inconsistent with the
rodent data. Using the same protocol, Buxton et al.
(1997) reported that physical exercise with a higher
intensity (75% of peak VO2) and a shorter duration
(1 h) elicited signiﬁcant phase-delay shifts when exer-
cise were cantered at a clock time of 0100 under dim
light (70–80 lux).11 The timing of the onset of the noc-
turnal elevations of plasma melatonin was used to esti-
mate the circadian phase before and after stimulus. The
mean phase delay shifts were −23 ± SE 10 min without
exercise, −63 ± SE 8 min with low intensity exercise of
3 h, and −55 ± SE 15 min with high intensity exercise of
1 h, respectively. These results suggested that a low
intensity of physical exercise was enough to shift the
human circadian clock. Recently, Buxton et al. (2003)
extended the experiment and demonstrated a PRC for
physical exercise (the data combined with 3-h low
intensity exercise and 1-h high intensity exercise).34 This
PRC revealed phase-advance shifts by physical exercise
in the evening and phase-delay shifts in the subjective
night. In addition, they indicated that physical exercise
in the morning and afternoon had no effect on the cir-
The question arises as to whether the phase-advance
shift by a single bout of exercise in the evening was
really due to the change in the circadian pacemaker,
since the phase determination was made at 1 to 2 cir-
cadian cycles immediately after the physical exercise.
Indeed, a phase-advance shift was obtained one cycle
after the exercise session (30 ± SE 15 min), but a larger
phase-delay shift (−66 ± SE 9 min) occurred on the fol-
Previously we examined the phase-shifting effects of a
single bout of physical exercise.35 In this experiment, the
subjects stayed three nights in the isolation facility. On
Day 1, the pre-exercise circadian phase was obtained.
On the Day 2, a single bout of 2 h of physical exercise
(intensity heart rate at 140 beat/min) was imposed at
one of the three times of day (morning 9:00–11:00,
afternoon 15:00–17:00 and night 00:00–02:00). As a
result, there was a slight but signiﬁcant phase-delay shift
of circadian rhythm in plasma melatonin when physical
exercise was performed in the afternoon and at night.
However, the amount of the phase shift was not signif-
icantly different from that of the control subjects who
stayed in the same isolation facility for three days with-
Beersma and Hiddinga (1998) examined the effects of
a single bout of physical exercise on the intrinsic period
(τ) of the human circadian pacemaker using a T-cycle
experimental procedure.36 Using a 20-h forced desyn-
chrony protocol (13.5 h for wakefulness and 6.5 h for
sleep), three experiments were conducted under dim
light conditions (under 10 lux), with and without phys-
ical exercise. The subjects performed two types of phys-
ical exercise using a cycle ergometer, with intermediate
and high intensity for a half hour per 2 h of each waking
time. They did not observe a signiﬁcant effect of phys-
ical exercise on the τ. In this study, the τ was assessed by
the demasked core body temperature rhythm, which
showed a larger variability in estimating the circadian
phase. Further research is needed to detect the effect
of physical exercise on the τ of human circadian
The mechanism induced a single bout of physical
exercise to phase shift the circadian rhythm is not yet
known. It is well established that the increase of rectal
temperature by physical exercise is greater in the early
morning than in the afternoon and late evening.37–39
Hypothermia after a single bout of physical exercise was
observed longer in the morning than in the afternoon
Recently, Kobayshi et al. (2005) examined the effects
of a single bout of physical exercise for 1 h with a
strength of 50–60% VO2 maximum at three different
time of day (morning 07:40–08:40, evening 16:30–
17:30, late evening 20:30–21:30) on the night’s sleep.40
They reported that 1 h physical exercise, when carried
out in the late evening, signiﬁcantly shortened sleep
latency and increased slow-wave sleep compared with
any other timed exercise. Furthermore, Tanaka et al.
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202 Journal compilation © 2006 Japanese Society of Sleep Research
(2001) have demonstrated that the intervention such as
a short nap after lunch (30 min between 13:00 and
15:00) and moderate intensity of exercise in the evening
(30 min from 17:00) was effective in improving sleep
quality for elderly people who have difﬁculty in sleep-
ing.41 They have suggested that the quality of the day-
time arousal of the elderly people was improved by
exercise in the evening.41 However, other previous stud-
ies have reported that moderate intensity exercise in
the morning or afternoon improved shorter sleep
latency42–44 and more slow-wave sleep.42,45
Since these studies did not measure the circadian
rhythm maker, it is not known that the subject’s circa-
dian pacemaker would really phase-advance shift as a
result of physical exercise. The precise mechanism of
these time-dependent phenomena is not yet known.
However, a change of body temperature and subjective
arousal by physical exercise cannot be excluded as
a possible factor which may entrain the circadian
Daily bouts of physical exercise
Previously, we reported that daily bouts of physical exer-
cise advanced the human circadian pacemaker.35 In
this experiment, physical exercise was imposed regu-
larly on subjects whose sleep/wake schedule was phase-
advanced by 20 min everyday (Fig. 2). The subjects
performed physical exercise with the bicycle ergometer
for 2 h twice during the waking period. The morning
exercise started at 3 h after wake up and the afternoon
exercise started within 2 h after the end of the morn-
ing exercise (7 h after wake up). In the control experi-
ment, the subjects were sitting in a chair at the same
time of day as physical exercise. The light intensity was
less than 10 lux. The circadian rhythm in plasma mela-
tonin was phase-advanced signiﬁcantly in the subjects
who took regular physical exercise during the waking
period, whereas the melatonin rhythm was not shifted
in the subjects without taking exercise (Fig. 3). These
ﬁndings indicate that regular physical exercise has a
potential to entrain the human circadian pacemaker.
However, it is not known whether the phase shift is due
to the direct effect of physical exercise, or the effect of
some other factors associated with physical exercise,
such as the increase in body temperature.
Possible explanations for the phase-advance shift
observed in a double-session exercise study were; (i) the
physical exercise phase-advanced the circadian rhythm;
or (ii) the physical exercise increased the arousal level,
which resulted in phase-advance shifts.
The question now arises as to why regular exercise
during the waking period induces phase-advance
shifts,35 which is inconsistent with the PRC reported by
Buxton et al. (2003).34 According to the PRC, physical
exercise beginning in the middle of the day produces a
phase delay, rather than a phase-advance shift. There-
fore we constructed a partial PRC using the previous
experiment,35 and found that physical exercise around
8 h after the melatonin peak produced phase-advance
shifts (Fig. 4). Since the time of physical exercise did not
cover the whole circadian phase, we need to complete
the PRC for physical exercise.
Physical exercise facilitate
Shift workers and transmeridian travelers are exposed to
the abnormal light/dark cycles and a change in the phase
Figure 2 Experimental protocol for scheduled sleep/wake
cycle with the period of 23 h 40 min (modiﬁed from
Miyazaki et al., 2001).35 Solid bars; rest period, hatched bars;
2 h physical exercise twice a day. The period indicated by the
two arrows is the time of serial blood sampling. The phase
angle difference was calculated between the plasma melato-
nin peak (downward triangles at Day 2 and Day 9) and mid-
point of physical exercise twice a day during a waking period
(upward triangles at Day 2 and Day 9). For calculating the
phase difference, the melatonin peak at Day 1 was used as the
substitute for the melatonin peak at Day 2 (see Fig. 4).
Time of day (hours)
Exercise and human circadian rhythms
© 2006 The Authors
Journal compilation © 2006 Japanese Society of Sleep Research 203
relationship between sleep and the endogenous circa-
dian rhythm. The internal and external desynchroniza-
tions induce various symptoms including fatigue,
headaches, irritability, loss of concentration, gastrointes-
tinal disorders and sleep problems (sleep loss, premature
awakening). In addition, the maximum performance of
physical exercise also declines as a result of jet lag.46
There is a question as to whether physical exercise
facilitates the resynchronization of the circadian rhythm
to a new time zone. In the animal study using Syrian
hamsters, Mrosovsky and Salmon (1987) revealed that a
single pulse of 3-h wheel running in the middle of the
rest period facilitated resynchronization to an 8-h
phase-advance shift of the light/dark cycle.47 In humans,
Klein and Wegman (1974) and Shiota et al. (1996) have
reported that outdoor exercise had some effect on the
resynchronization of circadian rhythms in urinary 17-
hydroxy corticosteroids and catecholamine exertion to a
new time zone. However, the light condition was not
controlled in these studies.48,49 Recently, Barger et al.
(2004) have examined whether physical exercise of
moderate intensity (65–75% heart rate maximim) facil-
itated resynchronization to a new sleep/wake cycle (9-h
delay of the subject’s habitual sleep episode).50 Subjects
carried out physical exercise for seven days following
the 9-h phase delay of the sleep/wake schedule, while
the control subjects were just sitting on the bicycle. The
light intensity was strictly controlled to 0.65 lux at
the standing position (angle of gaze). The mean phase
shift of the rising phase of plasma melatonin was signif-
icantly greater in the subjects doing physical exercise
(−3.17 ± SE 00.49 h) than in the control (−1.67 ± SE
00.45 h). In this experiment, physical exercise was done
4.2–6.7 h after the rising phase of plasma melatonin.
Thus, daily bouts of physical exercise facilitated the
resynchronization of the melatonin rhythm after a
phase-delay shift of sleep/wake cycle.
On the other hand, physical exercise was reported to
have no or a very small effect on the resynchronization
of circadian rhythms to a shift schedule.51,52 Both studies
simulated shift work with consecutive day/night shift
work (9-h delay from habitual sleep time). In one
study,51 during the 8 days of night work, physical exer-
cise at 50–60% of maximal heart rate was imposed for a
15-min duration in the ﬁrst three days. A larger phase
delay shift was observed in the temperature rhythm of
the subjects doing physical exercise, but it was not sig-
niﬁcantly different from that in the control subjects
(−6.6 ± SD 2.5 vs −4.2 ± SD 3.4 h). In the other study,52
intermittent physical exercise (6 bouts, 15-min long
each, at 50–60% of maximal heart rate) occurred during
Figure 3 Plasma melatonin rhythms on Day 1, Day 8 and
Day 14 of the experiment of the scheduled sleep/wake cycle.
The circadian rhythm in plasma melatonin was phase
advanced signiﬁcantly in subjects doing physical exercise
(), whereas the melatonin rhythm did not shift in the sub-
jects not doing exercise () (adapted from Miyazaki et al.
Plasma melatonin (%)Plasma melatonin (%)Plasma melatonin (%)
Time of day (hours)
16 0 8 16
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204 Journal compilation © 2006 Japanese Society of Sleep Research
the ﬁrst 6 h of the ﬁrst three night shifts. Exercise nei-
ther facilitated nor inhibited the phase shift induced by
bright light. In both experiments, physical exercise was
performed in the subjective night when the phase-delay
shift was expected.34 Similarly, Youngstedt et al. (2002)
failed to ﬁnd an additive effect of physical exercise on
bright light-induced phase shifts.53
EFFECT OF PHYSICAL EXERCISE IN
Almost all studies examining the effects of physical exer-
cise on circadian rhythms have been conducted in
young, healthy subjects. In elderly people, the circadian
rhythms in entrainment tend to phase advance as com-
pared with those in young subjects.54–58 In addition, the
amplitude of circadian melatonin and core body tem-
perature rhythms are low in elderly people.54–56,59,60
Notably, the phase relationship between sleep and the
circadian rhythm of minimum core body temperature
was reported to change in elderly people. The mecha-
nisms for these changes are not well understood. One
study addressed the issue and found that nocturnal
physical exercise induced phase-delay shifts of the cir-
cadian rhythm in plasma melatonin in elderly male and
female subjects.61 Phase shifts were also observed by a
single bout of physical exercise. Although the phase
shift in elderly people was not consistent in direction
[(phase advance (n = 2), phase delay (n = 5), no phase
shift (n = 1)], the result suggests that physical exercise is
useful in elderly people to adjust circadian rhythms to
the environmental cycle.
Nocturnal physical exercise induces signiﬁcant phase
delay shifts in the human circadian pacemaker. How-
ever, the effects of a single bout of physical exercise in
the daytime were not consistent among studies. On the
other hand, daily bouts of physical exercise facilitated
re-entrainment of the circadian melatonin rhythm to
advance or delay the sleep/wake cycle. These results
suggest that timed and regular physical exercise is useful
for the entrainment of the circadian rhythms in blind
people, shift workers, and jet-lagged travelers. However,
the optimal conditions of physical exercise still remain
to be clariﬁed.
1Atkinson G, Reilly T. Circadian variation in sports per-
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Figure 4 A partial phase-response curve to physical exercise twice a day during the waking period and control condition with-
out physical exercise from the shortened T cycle experiment.35 The phase shift derived from melatonin data from Day 1 to Day
8 and from Day 9 to Day 15 are plotted vs the mid-point of timing of stimulus relative to estimated timing of melatonin peak
for each subject on Day 2 and on Day 9. By convention, phase advances are deﬁned as positive numbers and phase delays as
negative numbers. The right panel shows the phase response to control conditions studied in the absence of physical exercise.
Open circles () represent the timing of the mid-point of rest conditions on Day 2 vs the phase shift of plasma melatonin from
Day 1 to Day 8, and open triangles () represent the timing of rest conditions on Day 9 vs the phase shift from Day 9 to Day
15. The left panel shows the phase response to 2 h of physical exercise twice a day. The ﬁlled circles () indicate the timing
of exercise twice on Day 2 vs the phase shift of plasma melatonin from Day 1 to Day 8, and the ﬁlled triangles () indicate
the timing of exercise on Day 9 vs the phase shift from Day 9 to Day 15.
Timing of physical exercise (hours after melatonin peak)
Phase shift (hours/ 7day)
02468101214 024681012 14
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Journal compilation © 2006 Japanese Society of Sleep Research 205
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