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

• Published in: European journal of applied physiology Vol. 116; no. 4; pp. 769 - 779
• Main Authors: Otani, Hidenori, Kaya, Mitsuharu, Tamaki, Akira, Watson, Phillip, Maughan, Ronald J.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-04-2016; Springer Nature B.V
• Subjects: Adult; Anaerobic Threshold - radiation effects; Biomedical and Life Sciences; Biomedicine; Body Temperature Regulation; Exercise; Exercise - physiology; Fatigue; Health sciences; Heart rate; Heat; Hemodynamics; Hot Temperature; Human Physiology; Humans; Humidity; Investigations; Male; Marathons; Occupational Medicine/Industrial Medicine; Original Article; Radiation; Random Allocation; Running; Skin; Sports Medicine; Sunlight - adverse effects; Temperature; Japan; Sunlight; Thermoregulation; Fatigue; Heat stress; Core temperature; Skin temperature
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-016-3335-9

Purpose
The present study investigated the effects of variations in solar radiation on endurance exercise capacity and thermoregulatory responses in a hot environment.
Methods
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/m
2
.
Results
Exercise time to exhaustion was less on the 800 W/m
2
trial (23 ± 4 min) than on all the other trials (500 W/m
2
30 ± 7 min;
P
 < 0.05, 250 W/m
2
43 ± 10 min;
P
 < 0.001, 0 W/m
2
46 ± 10 min;
P
 < 0.001), and on the 500 W/m
2
trial than the 250 W/m
2
(
P
 < 0.05) and 0 W/m
2
(
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/m
2
trial than the 250 and 0 W/m
2
trials (
P
 < 0.05), and on the 500 W/m
2
trial than the 0 W/m
2
trial (
P
 < 0.05). The core-to-skin temperature gradient was narrower on the 800 W/m
2
trial than the 250 and 0 W/m
2
trials (
P
 < 0.05).
Conclusion
The present study demonstrates that endurance exercise capacity in a hot environment falls progressively as solar radiation increases.