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Effects of solar radiation on endurance exercise capacity in a hot environment

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The present study investigated the effects of variations in solar radiation on endurance exercise capacity and thermoregulatory responses in a hot environment.


Eight male volunteers performed four cycle exercise trials at 70 % maximum oxygen uptake until exhaustion in an environmental chamber maintained at 30 °C and 50 % relative humidity. Volunteers were tested under four solar radiation conditions: 800, 500, 250 and 0 W/m2.


Exercise time to exhaustion was less on the 800 W/m2 trial (23 ± 4 min) than on all the other trials (500 W/m2 30 ± 7 min; P < 0.05, 250 W/m2 43 ± 10 min; P < 0.001, 0 W/m2 46 ± 10 min; P < 0.001), and on the 500 W/m2 trial than the 250 W/m2 (P < 0.05) and 0 W/m2 (P < 0.01) trials. There were no differences in core (rectal) temperature, total sweat loss, heart rate, skin blood flow, cutaneous vascular conductance and percentage changes in plasma volume between trials (P > 0.05). Mean skin temperature was higher on the 800 W/m2 trial than the 250 and 0 W/m2 trials (P < 0.05), and on the 500 W/m2 trial than the 0 W/m2 trial (P < 0.05). The core-to-skin temperature gradient was narrower on the 800 W/m2 trial than the 250 and 0 W/m2 trials (P < 0.05).


The present study demonstrates that endurance exercise capacity in a hot environment falls progressively as solar radiation increases.

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Analysis of variance


Cutaneous vascular conductance


Heart rate


Relative humidity


Rating of perceived exertion


Ambient temperature


Rectal temperature


Mean skin temperature


Maximum oxygen uptake


Wet-bulb globe temperature


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The authors thank the volunteers who donated their time and effort to participate in the present study. The authors also thank Dr. Takanori Yamamoto for technical assistance and Ken Shimizu, Tetsuki Okada, Yorito Kakimoto and Yuta Masuno for assistance. This study was funded by Japan Society for the Promotion of Science KAKENHI (Grant Number 26870759).

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Correspondence to Hidenori Otani.

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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

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Communicated by Narihiko Kondo.

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Otani, H., Kaya, M., Tamaki, A. et al. Effects of solar radiation on endurance exercise capacity in a hot environment. Eur J Appl Physiol 116, 769–779 (2016).

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