Exercise temperature regulation following a 35-day horizontal bedrest.

• 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 (Wpeak ; 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 Wpeak (i.e., at a fixed absolute intensity; POST-A), and (ii) the post-bedrest Wpeak (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 (Trec ) 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 Trec 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. Trec 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.

Nyckelord

core temperature

detraining

exertional hyperthermia

heat loss

inactivity

sweating rate

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