Author(s): DUTRA, Y., TEIXEIRA, M.V.S., MENDONÇA, P.T., GOODALL, S., ZAGATTO, A.M., Institution: UNESP , Country: BRAZIL, Abstract-ID: 1529

INTRODUCTION:
While sex-related differences in fatigability are established in temperate conditions [1], the influence on exercise responses under heat stress remains less understood [2]. This study aimed to investigate sex-related differences in fatigability induced by exercise under heat stress.
METHODS:
Twelve females (F) and fourteen males (M) of similar training status (maximal oxygen uptake: 45.2 and 53.4 mL/kg/min; maximal metabolic steady state: 59 and 62% of peak power output, for F and M, respectively) completed cycling trials to task failure in the heavy domain in temperate (CONT; 21°C, 52% RH) and hot (HEAT; 42°C, 33% RH) environments. During exercise, core temperature and rate of perceived effort were recorded every 2- and 4-min, respectively. Before, after 30-min of exercise, and at task failure, brief (3-s) and long (1-min) maximal voluntary contractions (MVCs) of the knee extensors were performed with peripheral nerve stimulation delivered during along with electromyography activity (EMG) of vastus lateralis being recorded. Where necessary, repeated-measures ANOVA with three (condition, time, sex) or two (condition, sex) factors were used to evaluate the effects of environment, exercise, and sex on the outcomes. Statistical significance was set at p<0.05.
RESULTS:
There was no difference in time to task failure (TTF) between sexes in either CONT (F= 97±26 min; M= 89±26 min) or HEAT (F= 37±8 min; M= 35±5 min – condition×sex interaction, p=0.54). Throughout exercise in HEAT, F and M showed similar increases (i.e., linear slope) in core temperature (F=+0.03°C/min; M=+0.04°C/min) and perceived effort (F=+0.12 a.u./min; M=+0.14 a.u./min – condition effect, p<0.01; condition×sex interaction, p>0.20). After 30-min of effort, heat stress exacerbated reductions in voluntary activation during brief MVCs (−5%) along with decrements in mean force and in the ratio of the root mean square of EMG to the amplitude of the evoked M-wave (RMS/M-wave) during long MVCs (−13% and −33%, respectively – condition×time interaction, p<0.01). These changes were similar between sexes (condition×time×sex interaction, p>0.42). At task failure, F presented greater reduction in RMS/M-wave during brief MVC than M (−39% and −13%, respectively), whereas M presented greater reduction in M-wave than F (−32% and 3%, respectively – condition×time×sex interaction, p<0.02). Specifically in F, heat-induced changes in TTF correlated (p<0.05) with both heat-induced exacerbation of perceived effort (r=¬−0.66) and the decline in RMS/M-wave during long MVC (r=0.78).
CONCLUSION:
Heat stress reduced TTF similarly for both sexes but exacerbated central fatigue in F and worsened the impairment in sarcolemma action potential propagation in M. Correlational results suggest that the heat-induced increase in perceived effort and exacerbation of central fatigue may contribute to impaired performance of F when exercising under heat stress.

1. Ansdell et al., 2020 2. Périard et al., 2021