Rhythms during hypokinesis.

The circadian rhythms of body temperature (BT) and heart rate (HR) w ere studied in 12 healthy males. Asynchrony of BT and HR was establishe d without changing the photoperiod by complete bed rest without exercise. This asynchrony was characterized by marked phase-shiftings and a decrease in the amplitude of BT and HR. The latter change returned to normal in the post-bed-rest period. Lowered BT and transient bradycardia were observed within the 1st 2 days of bed rest. Asynchrony of the rhythms was most evident on the 23rd day of bed rest. This was accompanied by sudden phase-shifting and a 50% increase in HR which was not attributable to prolonged inactivity or the confinement implicit in bed rest. It is suggested that the reduction of proprioceptive receptor stimuli requires a compensatory increase of other environmental synchronizers to maintain rhythm synchrony.