O. Vanreeth et al., NOCTURNAL EXERCISE PHASE DELAYS CIRCADIAN-RHYTHMS OF MELATONIN AND THYROTROPIN SECRETION IN NORMAL MEN, The American journal of physiology, 266(6), 1994, pp. 50000964-50000974
To determine whether a single episode of physical activity is capable
of inducing rapid phase shifts in human circadian rhythms, 17 subjects
were studied two times under constant routine conditions, once in the
absence of stimulus and once with a 3-h nighttime pulse of exercise i
nterrupting the constant routine conditions. The profiles of plasma co
rtisol, thyrotropin (TSH), and melatonin and of body temperature were
monitored continuously to derive estimations of circadian phase positi
on. The phase shifts were measured on the Ist day after exercise expos
ure. The timing of the exercise period ranged from -5 h to +4 h around
the time of the minimum body temperature rhythm. Nighttime exercise w
as associated with 1- to 2-h phase delays of both the melatonin and TS
H rhythms, with the size of the delays tending to be smaller when the
exercise was presented in the latter part of the nighttime period and
in the early morning. These data demonstrate that nonphotic stimuli ma
y exert phase-shifting effects on the human circadian pacemaker.