NEW FINDINGS: What is the central question of this study? Does a 35-day horizontal bedrest impair thermoeffector responses during whole-body submaximal exercise performed in temperate conditions? What is the main finding and its importance? Cardiovascular and muscular deconditioning ensued from prolonged recumbency, seems to augment, at least to a degree, the exercise-induced increase in body core temperature, most likely due to an impairment in non-evaporative heat loss. The response is a function of the absolute exercise intensity imposed.

ABSTRACT: We examined the effects of a 35-day horizontal bedrest on thermoregulation during whole-body exercise. Fifteen healthy men were randomly assigned to either a bedrest (BR; n = 10), or a control (CON; n = 5) group. Prior to bedrest, both groups performed a 40-min constant-load upright cycling at 30% of their peak workload (W_peak ; PRE). One and two days after bedrest, the BR group performed, in a randomised counterbalanced order, two 40-min trials at 30% of: (i) the pre-bedrest W_peak (i.e., at a fixed absolute intensity; POST-A), and (ii) the post-bedrest W_peak (i.e., at a fixed relative intensity; POST-R). The CON group conducted only the POST-A trial, at the same time intervals. During the trials, rectal (T_rec ) and skin temperatures, and the forehead sweating rate (SwR) were monitored. In the CON group, no differences were observed between the trials. Bedrest potentiated moderately the T_rec elevation during the latter part of POST-A (∼0.10°C; P≤0.05), but not of POST-R (∼0.04°C; P = 0.11). In both post-bedrest trials, was attenuated by ∼1.5-2.0^° C throughout (P<0.01), whereas the forehead SwR was not modulated. T_rec and were similar in POST-A and POST-R; yet the forehead SwR was more dependent on the relative workload imposed (P = 0.04). Present findings therefore suggest that the cardiovascular and muscular deconditioning ensued from a 35-day bedrest may aggravate the exercise-induced increase in body core temperature when working at a given absolute intensity, most likely due to an impairment in non-evaporative heat loss. This article is protected by copyright. All rights reserved.