title: Effects of solar radiation on endurance exercise capacity in a hot environment.
abstract: OBJECTIVE
  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).
  
  
  CONCLUSIONS
  The present study demonstrates that endurance exercise capacity in a hot environment falls progressively as solar radiation increases.
authors: Faculty of Health Care Sciences, Himeji Dokkyo University, 7-2-1 Kamiono, Himeji, Hyogo, 670-8524, Japan. hotani@himeji-du.ac.jp.
authors: Hidenori
authors: H
authors: Otani
authors: Hyogo University of Health Sciences, Kobe, Hyogo, Japan.
authors: Mitsuharu
authors: M
authors: Kaya
authors: Hyogo University of Health Sciences, Kobe, Hyogo, Japan.
authors: Akira
authors: A
authors: Tamaki
authors: Department of Human Physiology, Vrije Universiteit Brussel, Brussels, Belgium.
authors: Phillip
authors: P
authors: Watson
authors: School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire, UK.
authors: Ronald J
authors: RJ
authors: Maughan
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold / Q000528:radiation effects*; D001833:Body Temperature Regulation; D015444:Exercise / Q000502:physiology*; D006439:Hemodynamics; D006358:Hot Temperature; D006801:Humans; D008297:Male; D011897:Random Allocation; D013472:Sunlight / Q000009:adverse effects*
keywords: Core temperature; Fatigue; Heat stress; Skin temperature; Sunlight; Thermoregulation