Exercise Performance and Thermoregulatory Responses of Elite Athletes Exercising in the Heat: Outcomes of the Thermo Tokyo Study

Abstract

Objective: We examined the impact of simulated Tokyo 2020 environmental condition on exercise performance, thermoregulatory responses and thermal perception among Dutch elite athletes.

Methods: 105 elite athletes from different sport disciplines performed two exercise tests in simulated control (15.9 ± 1.2 °C, relative humidity (RH) 55 ± 6%) and Tokyo (31.6 ± 1.0 °C, RH 74 ± 5%) environmental conditions. Exercise tests consisted of a 20-min warm-up (70% HR_max), followed by an incremental phase until volitional exhaustion (5% workload increase every 3 min). Gastrointestinal temperature (T_gi), heart rate, exercise performance and thermal perception were measured.

Results: Time to exhaustion was 16 ± 8 min shorter in the Tokyo versus the control condition (- 26 ± 11%, whereas peak power output decreased with 0.5 ± 0.3 W/kg (16 ± 7%). Greater exercise-induced increases in T_gi (1.8 ± 0.6 °C vs. 1.5 ± 0.5 °C, p < 0.001) and higher peak T_gi (38.9 ± 0.6 °C vs. 38.7 ± 0.4 °C, p < 0.001) were found in the Tokyo versus control condition. Large interindividual variations in exercise-induced increase in T_gi (range 0.7-3.5 °C) and peak T_gi (range 37.6-40.4 °C) were found in the Tokyo condition, with greater T_gi responses in endurance versus mixed- and skill-trained athletes. Peak thermal sensation and thermal comfort scores deteriorated in the Tokyo condition, with aggravated responses for power versus endurance- and mixed-trained athletes.

Conclusion: Large performance losses and T_gi increases were found among elite athletes exercising in simulated Tokyo conditions, with a substantial interindividual variation and significantly different responses across sport disciplines. These findings highlight the importance of an individual approach to optimally prepare athletes for safe and maximal exercise performance during the Tokyo Olympics.

Fig. 1

Group data (panels A + B) and individual data (panels C + D) of time to exhaustion (TTE) (panels A + C) and peak power output (PPO) (panels B + D) in the Tokyo condition relative to the control condition. Data in the upper panels are presented as mean ± SD. The relative changes in exercise performance were not different across sport disciplines. Each bar of panels C and D represent data from an individual athlete, highlighting the large interindividual variability in changes in exercise performance during exercise in the heat

Fig. 2

A Exercise-induced increases in gastrointestinal temperature (T_gi), B skin temperature (T_sk) and C heart rate (HR) during the control (blue lines) and Tokyo (red lines) conditions. A An increase in T_gi was observed in both conditions, with greater values in the Tokyo versus the control condition. B T_sk increased over time with greater values in the Tokyo versus the control condition. C HR values increased over time in both conditions, with higher values in the Tokyo versus the control condition. Data are presented as mean ± SD for all time points with a sample size > 10% of our cohort

Fig. 3

Group data (panels A + B) and individual data (panels C + D) of peak gastrointestinal temperature (T_gi) achieved during the control (panels A + C) and Tokyo (panel B + D) conditions. Data in the upper panels are presented as mean ± SD. Endurance athletes demonstrated a significantly higher peak T_gi in the Tokyo condition compared to mixed and skill athletes. Each bar of panels C and D represent data from an individual athlete, whereas the largest interindividual variability can be observed in the Tokyo condition

Fig. 4

Correlations between percentual changes in time to exhaustion (panels A + C) and peak power output (panels B + D) and the exercise-induced T_gi increase (panels A + B) and peak T_gi (panels C + D) in the Tokyo condition. Neither peak T_gi nor exercise-induced increase in T_gi were associated with the changes in time to exhaustion or peak power output between the Tokyo and control conditions