Roles of intensity and duration of nocturnal exercise in causing
phase delays of human circadian rhythms.
Buxton, Orfeu M., Samuel A. Frank, Mireille L'hermite
-Bal[umlaut]ariaux, Rachel Leproult, Fred W. Turek, and Eve Van
Cauter.
Department of Medicine, University of Chicago, Illinois, 60637,
Neurobiology and Physiology Department, Northwestern University,
Evanston, Illinois, 60208, Laboratory of Experimental Medicine,
Universit[umlaut]a Libre de Bruxelles, B-1070 Brussels, Belgium
APStracts 4:0113E, 1997.
To determine the role of intensity and duration of nocturnal physical
activity in causing rapid phase-shifts of human circadian rhythms, 8
healthy men were studied three times under constant conditions with
no exercise, a 3hr bout of moderate intensity exercise, or a 1hr bout
of high intensity exercise. Exercise stimulus was centered at 01:00
(1am). Circadian phase was estimated from the onsets of the nocturnal
elevation of plasma thyrotropin (TSH) and melatonin. Mean phase
shifts of TSH onsets were -188 min (baseline), -7810 min (low
intensity exercise, p<.01), and -9519 min (high intensity exercise,
p<.01). Mean phase delays of melatonin onsets were -2310 min
(baseline), -638 min (low intensity exercise, p<.04), and -5515 min
(high intensity exercise, p<.12). Taken together with our previous
findings, this study indicates that nocturnal physical activity may
phase delay human circadian rhythms and demonstrates that phase
-shifting effects may be determined with exercise durations and
intensities compatible with the demands of a real life setting.
Received 5 March 1997; accepted in final form 6 May 1997.
APS Manuscript Number E102-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 11 June 1997