The effect of head-to-head competition on behavioural thermoregulation, thermophysiological strain and performance during exercise in the heat

Background - It has been suggested that pacing is a thermoregulatory behaviour. We investigated the effect of competition on pacing, performance, and thermophysiological strain during exercise in the heat and the psychological factors mediating competition effects.

Method - Eighteen males (VO_2max=3.69(0.44) L·min^-1) undertook a preliminary 20 km cool (WBGT=12°C) cycling time-trial (TT) and three experimental 20 km trials (balanced order): i) cool TT (CoolSolo); ii) hot (WBGT=26°C) TT (HotSolo); iii) hot head-to-head competition (HotH2H). During TTs an avatar of the participant’s performance was visible. During HotH2H participants believed they were competing against another participant, but the competitor’s avatar replicated their own preliminary (cool) TT.

Results - TTs (min:sec) slowed with increased ambient temperature (CoolSolo=35:31(2:11) vs. HotSolo=36:10(2:26), P=0.011). This effect was negated by competition; performances were not different between HotH2H (35:17(1:52) and CoolSolo (P=0.160) and were quicker in HotH2H vs. HotSolo (P=0.001). End-exercise rectal temperature, mean body temperature and physiological strain index were (P<0.05) higher in HotH2H than either solo condition. Despite faster performance and greater thermophysiological strain, RPE, thermal comfort and sensation, and perceptual strain index were not different between HotH2H and HotSolo. The Δ in end-exercise rectal temperature between HotH2H vs. HotSolo was related to pre-exercise anticipatory heart rate response (r=0.608, P=0.010) and participants’ propensity for deliberate risk-taking (B=0.12, P<0.001), whereas self-reported resilience predicted Δ performance times between HotH2H vs. HotSolo (B=-9.40, P=0.010).

Conclusion - Competition changes the relationship between perceived and actual thermophysiological state, altering behavioral thermoregulation and increasing thermophysiological strain; this could increase heat-illness risk. Psychophysiological and psychological measures may identify susceptible individuals.