Mental fatigue accompanied with whole body cold exposure before exercise impairs endurance exercise performance

Abstract

Purpose Endurance exercise performance is impaired by cold exposure before exercise via an enhanced sympathetic activation. Mental fatigue induced by psychological task before exercise deteriorates endurance exercise performance, but the impact of a simultaneous load of mental fatigue and cold exposure on endurance exercise performance is remained unknown. The purpose of this study is to test the hypothesis that mental fatigue during cold exposure before exercise further impairs endurance exercise performance. Methods Nine male young subjects performed the Stroop color word test (500 stimuli/set×2, 55 min in total) as mental stress (MS) trial, while watched a documentary DVD as control (CON) trial during whole body cold exposure using a water-perfused suit (10˚C for 10 min then 15˚C for 50 min). After that participants performed a cycling test at 80% VO2max to the exhaustion after warm-up for 4 min. Subjective fatigue index (SFI) were measured before and immediately after mental stress and exercise. Plasma adrenaline ([Ad]p), noradrenaline ([Norad]p), and cortisol ([Corti]p) concentrations were measured before and immediately after mental load and exercise. Time to exhaustion (TE) was evaluated as endurance cycling performance. This study received an ethics approval from our institution. Results Percent changes from baseline of SFI were higher in the MS trial than in the CON trial at post Intervention and post exercise (p < 0.001). Significant effects of interaction (time × trial) were found on [Ad]p (p = 0.026), while not on [Norad]p nor on [Corti]p. TE was shortened but not significantly for the MS trial (767 ± 63 s) compared with the CON trial (813 ± 51 s), and an effect size of the difference was d = 0.271. The difference (Δ) between the trials (MS - CON) of TE was negatively correlated with Δ[Ad]p (r = - 0.605, p = 0.085) or Δ[Norad]p (r = - 0.661, p = 0.074), but not with Δ[Corti]p (r=0.251, p=0.514) determined immediately after exercise. Conclusions These findings support our hypothesis, thus mental fatigue accompanied with whole body cold exposure before exercise would further impair endurance exercise performance compared with cold exposure alone via the enhanced sympathoadrenal medullary system rather than hypothalamic pituitary adrenal system.