Effects of hot and humid environments on thermoregulation and aerobic endurance capacity of Laser sailors

OBJECTIVES: The purpose was to investigate the effects of hot and humid environments on thermoregulation and aerobic endurance capacity and whether high skin temperature serves as a more important thermoregulatory factor affecting aerobic exercise capacity. METHODS: A randomized cross-over design was applied to this study, in which nine Laser sailors performed the 6 km rowing test (6 km test) in both a warm (ambient temperature: 23 ± 1.4 °C; relative humidity: 60.5 ± 0.7%; wind speed: 0 km/h; WARM) and hot environment (ambient temperature: 31.8 ± 1.1 °C; relative humidity: 63.5 ± 4.9%; wind speed: 3.5 ± 0.7 km/h; HOT). RESULTS: The time for completing 6 km test of HOT group was significantly longer than that of WARM group (P = 0.0014). Mean power of 3–4 km, 4–5 km and 5–6 km were significant lower in HOT group (P = 0.014, P = 0.02, P = 0.003). Gastrointestinal temperature and skin temperature were significantly higher in HOT group during the 6 km test (P = 0.016, P = 0.04). Heat storage at 5 min and 15 min of HOT group were significantly higher than that of WARM group (P = 0.0036; P = 0.0018). Heart rate and physiological strain index of HOT group were significantly higher than that of WARM group during the 6 km test (P = 0.01, P < 0.01). CONCLUSION: When skin temperature and core temperature both increased, high skin temperature may be the more important thermoregulatory factor that affected the aerobic endurance performance in hot and humid environments. The high skin temperature narrowed the core to skin temperature gradient and skin to ambient temperature gradient, which may result in greater accumulation of heat storage. The greater heat storage led to the lower muscle power output, which contributed to the reduction of the heat production.