| Keywords |
Body temperature; Heat stress; Muscular strength; Peripheral fatigue; Dehydration |
| Abstract |
The purpose of this study was to assess the effects of hyperthermia on isometric handgrip strength and endurance.
Twelve healthy men completed two experimental trials: active hyperthermia (AH) involving treadmill exercise at 60% VO2max or passive hyperthermia (PH) via water garment until their rectal temperature (Tre) increased 1.5°C in ambient heat (35°C, 50%). Isometric handgrip strength and endurance were assessed on the dominant arm using a handheld dynamometer for maximal voluntary contraction (MVC), dynamic endurance (MVC10), and static endurance (MVC75%) immediately before and after hyperthermia. Exposure time to PH was significantly longer than AH, leading to a higher level of dehydration (AH: 0.9±0.1, PH: 1.4±0.3 kg) and forearm muscle temperature in PH (AH: 35.7±0.8, PH: 38.3±0.5°C) (p < 0.001). MVC did not change within or between the conditions. MVC10 was significantly impaired only in PH compared to AH (p=0.001) whereas MVC75% was significantly impaired at a similar degree in AH and PH (p<0.001). The study findings suggest that sustained force production ability is impaired following either mode of hyperthermia, whereas MVC remained unaffected. Together with hyperthermia-induced central fatigue, dehydration and high muscle temperature also appeared to influence handgrip strength and endurance. |