Figure 2. Heart rate (A), rating of perceived exertion (B) and rating of thermal comfort (C) during session 1 and session 5 of high intensity interval training (HIIT 1 and HIIT 5) in the Acc group who performed exercise in the heat (temperature = 38.7 ± 0.5 °C, relative humidity = 34.4 ± 1.3 %) and Con who exercised at room temperature (22.3 ± 0.2 °C; 35.8 ± 0.6 %). Values are mean ± SD, n = 7 per group. Difference between HIIT 1 and HIIT 5 at the corresponding time point within the Acc group, * p < 0.05. Mean rating of perceived exertion (RPE) during HIIT 1 in Acc is different from HIIT 5 in Acc, # p < 0.05. Acc: acclimation, Con:control.