title: Determinants of endurance exercise capacity in the heat in prepubertal boys.
abstract: The goal of this study was to identify factors which limit exercise endurance in hot ambient conditions in prepubertal boys. Eight healthy non-acclimatized, highly physically active prepubertal boys performed steady load cycling at approximately 65 % peak VO (2) to exhaustion in both cool (19.6 +/- 0.6 degrees C, 66.4 +/- 11.0 % relative humidity) and hot (31.0 +/- 0.3 degrees C, 56.9 +/- 2.0 % relative humidity) environmental conditions. Cardiac output, oxygen uptake, rectal temperature (T (re)), rating of perceived exertion (RPE), blood pressure, and calculated arterial venous oxygen difference were obtained serially in each testing session, and percent dehydration was calculated from body weight loss. Endurance time was significantly shorter in the hot condition (29.30 +/- 6.19 minutes versus 41.38 +/- 6.30 minutes in the cool room). No significant differences in circulatory markers or hydration status were observed either during testing or between cycling thermal conditions. Rate of rise of T (re) was greater during exercise in the heat, but no significant difference in T (re) between conditions was observed at exhaustion. Mean values of RPE were consistently greater during exercise in the heat, but these differences did not reach statistical significance. These findings support the concept that rises in core temperature and/or brain perception (RPE) rather than circulatory insufficiency may be the critical factors defining limits to exercise in the heat.
authors.affiliation: Department of Pediatrics, Baystate Medical Center, Springfield, MA 01106, USA. thomas.rowland@bhs.org
authors.forename: T
authors.initials: T
authors.lastname: Rowland
authors.forename: A
authors.initials: A
authors.lastname: Garrison
authors.forename: D
authors.initials: D
authors.lastname: Pober
mesh_terms: D001794:Blood Pressure / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D002648:Child; D003080:Cold Temperature; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D011627:Puberty / Q000502:physiology*; D015431:Weight Loss / Q000502:physiology
chemical_list: D010100:Oxygen