In a hot–dry environment racewalking increases the risk of hyperthermia in comparison to when running at a similar velocity

The purpose of this study was to determine if in a hot–dry environment, racewalking increases intestinal temperature (T_int) above the levels observed when running either at the same velocity or at a similar rate of heat production. Nine trained racewalkers exercised for 60 min in a hot–dry environment (30.0 ± 1.4°C; 33 ± 8% relative humidity; 2.4 m s⁻¹ air speed) on three separate occasions: (1) racewalking at 10.9 ± 1.0 km h⁻¹ (Walk), (2) running at the same velocity (RunVel) and (3) running at 13 ± 1.8 km h⁻¹ to obtain a similar \( \dot{V}{\text{O}}_{2} \) than during Walk (Run\( \dot{V}{\text{O}}_{2} \)). As designed, energy expenditure rate was similar during Walk and Run\( \dot{V}{\text{O}}_{2} \), but lower during RunVel (842 ± 78 and 827 ± 75 vs. 713 ± 55 W; p < 0.01). Final T_int was lower during RunVel than during both Walk and Run\( \dot{V}{\text{O}}_{2} \) (38.4 ± 0.3 vs. 39.2 ± 0.4 and 39.0 ± 0.4°C; p < 0.01). Heart rate and sweat rate were also lower during RunVel than during Walk and Run\( \dot{V}{\text{O}}_{2} \) (i.e. heart rate 159 ± 13 vs. 179 ± 11 and 181 ± 11 beats min⁻¹ and sweat rate 0.8 ± 0.3 vs. 1.1 ± 0.3 and 1.1 ± 0.3 L h⁻¹; p < 0.01). However, we could not detect differences in skin temperature among trials. In conclusion, our data indicate that in a hot–dry environment racewalking increases the risk of hyperthermia in comparison with when running at a similar velocity. However, exercise mode (walking vs. running) had no measurable impact on T_INT or heat dissipation when matched for energy expenditure.