Critical power (CP) delineates the heavy and severe exercise intensity domains, and sustained work rates above CP result in an inexorable progression of oxygen uptake to a maximal value and, subsequently, the limit of exercise tolerance. The finite work capacity above CP, W′, is defined by the curvature constant of the power-duration relationship. Heavy or severe exercise in a hot environment generates additional challenges related to the rise in body core temperature (Tc) that may impact CP and W′. The purpose of this study was to determine the effect of elevated Tc on CP and W′. CP and W′ were estimated by end-test power (EP; mean of final 30s) and work above end-test power (WEP), respectively, from 3-min "all-out" tests performed on a cycle ergometer. Volunteers (n = 8, 4 female) performed the 3-min tests during a familiarization visit and two experimental visits (Thermoneutral vs Hot, randomized crossover design). Before experimental 3-min tests, subjects were immersed in water (Thermoneutral: 36°C for 30 min; Hot: 40.5°C until Tc was ≥ 38.5°C). Mean Tc was significantly greater in Hot compared to Thermoneutral (38.5±0.0°C vs. 37.4±0.2°C; mean±SD, P<0.01). All 3-min tests were performed in an environmental chamber (Thermoneutral: 18°C, 45% RH; Hot: 38°C, 40% RH). EP was similar between Thermoneutral (239 ± 57W) and Hot (234 ± 66W; P = 0.55). WEP was similar between Thermoneutral (10.9 ± 3.0 kJ) and Hot (9.3 ± 3.6; P = 0.19). These results suggest that elevated Tc has no significant impact on EP or WEP.
Critical Power (CP) separates the heavy and severe exercise domains, and work above CP (defined as W′) results in an inexorable progression to maximal oxygen uptake and rise in blood lactate concentration to fatigue. The thermoregulatory demands accompanying a rise in body core temperature (Tc) compounded with the cardiovascular challenges presented by maximal exercise in a hot environment may impact CP and W′. To date, no study has explored the effects of elevated Tc and environmental temperature on CP and W′. The purpose of this study is to determine the effect of high environmental and Tc on CP and W′. CP was estimated as end test power (average of the last 30 sec) from a series of three‐min “all out” tests (3MT). Volunteers (n=7, 3F) performed a 3MT during a familiarization visit and two experimental study days (thermoneutral and hot) in a randomized crossover design. Prior to the 3MT in both experimental conditions, subjects were immersed in either thermoneutral (36°C for 30 min) or hot (40.5°C) water until Tc was ≥ 38.5°C. All 3MT were performed in an environmental chamber controlling for both temperature and humidity (18°C and 45% RH for thermoneutral; 38°C and 40% RH for hot). A paired t‐test was used for statistical analysis and data are presented as mean ± SE. Although variable, CP was similar between thermoneutral (245 ± 22W) and hot (243 ± 25; p=0.83), while W’ was only mildly reduced from thermoneutral (11 ± 1 kJ) to hot (9 ± 2) p=0.17. Total work performed was similar between thermoneutral (55 ± 5 kJ) and hot (53 ± 5) conditions (p=0.27) and peak power was similar between thermoneutral (827 ± 89W) and hot (809 ± 85) p=0.49. These preliminary data suggest that high Tc and environmental temperature, per se, appear to have no significant impact on CP as estimated by a 3‐minute all‐out test.
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