Consequences Of Rising Humidity Level On Circulatory Responses During Prolonged Intense Exercise

Ahmad Munir Che Muhamed, Martin William Thompson


The combined metabolic and thermoregulatory demands experienced during exercise in the heat impose an exceptional stress on the circulatory system. To date, much of what is known about circulatory stress during exercise in the heat has focused on primarily dry environment (~ 40% rh) with limited studies carried in higher humidity (> 60% rh) conditions. This study was designed to investigate the influence of humid condition on circulatory responses during prolonged intense running exercise among elite runners. On separate days, 11 male elite runners ran for 60 minutes at an intensity of 70% VO2 max across three different humidity levels of HH (71% rh), NH (43% rh) and LH (26.2% rh) with the ambient temperature set at 300C. Thermal stress was found to increase during exercise in the HH condition as both Tre and Tsk steadily rise across time. Circulatory stress markedly increased during exercise in higher humidity levels. Heart rate was significantly higher in the HH condition with its level increasing to 92% of HRmax. The upwards drift in HR was significantly higher in HH within the last ten minutes of exercise. Contrary, stroke volume recorded a steady decline during exercise with a significantly lower SV in the HH as compared with the NH and LH. Results implicate rising humidity level will impose greater circulatory stress during prolonged intense exercise. The consequence from this circulatory stress will result in limited ability for an athlete to sustain his exercise capacity when HR reaches maximal level.


cardiovascular drift; humidity; prolonged exercise; thermoregulation

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