Journal of Applied Physiology, Vol 48, Issue 6 1020-1023, Copyright © 1980 by American Physiological Society
Muscular work as thermal behavior in humans
M. Caputa and M. Cabanac
Human subjects were placed on a bicycle ergometer and left to pedal ad lib.
for 43 min to warm themselves and thereby attain thermal comfort at an
ambient temperature of 10 degrees C. Esophageal (Tes), tympanic (Tty),
forehead, and hand skin temperatures were recorded. In addition, the work
of pedaling was noted for each 2-min period. In some experiments sweating
rate was also recorded. Two series of experiments were performed, the first
with face fanning and the second with thermal insulation of the head. Face
fanning resulted in decreased Tty, but in substantially increased Tes,
which was 1.5 degrees C higher than Tty after an intense pedaling effort of
46-50 W. In experiments with head covering, a mild increase of both Tes and
Tty was observed toward a position halfway between the extreme values
obtained during face fanning. Simultaneously, pedaling intensity decreased
to 16.7 W and the rate of sweating increased. In general, pedaling work was
inversely proportional to intracranial temperature (Tty) and independent of
trunk temperature (Tes). Therefore, motivation for muscular activity in
humans exposed to cold appears to be goverened chiefly by the brain
temperature.
