title: Self-paced exercise in hot and cool conditions is associated with the maintenance of %V̇O2peak within a narrow range.
abstract: This study examined the time course and extent of decrease in peak oxygen uptake (V̇O2peak) during self-paced exercise in HOT (35°C and 60% relative humidity) and COOL (18°C and 40% relative humidity) laboratory conditions. Ten well-trained cyclists completed four consecutive 16.5-min time trials (15-min self-paced effort with 1.5-min maximal end-spurt to determine V̇O2peak) interspersed by 5 min of recovery on a cycle ergometer in each condition. Rectal temperature increased significantly more in HOT (39.4 ± 0.7°C) than COOL (38.6 ± 0.3°C; P < 0.001). Power output was lower throughout HOT compared with COOL (P < 0.001). The decrease in power output from trial 1 to 4 was ∼16% greater in HOT (P < 0.001). Oxygen uptake (V̇o2) was lower throughout HOT than COOL (P < 0.05), except at 5 min and during the end-spurt in trial 1. In HOT, V̇O2peak reached 97, 89, 85, and 85% of predetermined maximal V̇o2, whereas in COOL 97, 94, 93, and 92% were attained. Relative exercise intensity (%V̇O2peak) during trials 1 and 2 was lower in HOT (∼84%) than COOL (∼86%; P < 0.05), decreasing slightly during trials 3 and 4 (∼80 and ∼85%, respectively; P < 0.05). However, heart rate was higher throughout HOT (P = 0.002), and ratings of perceived exertion greater during trials 3 and 4 in HOT (P < 0.05). Consequently, the regulation of self-paced exercise appears to occur in conjunction with the maintenance of %V̇O2peak within a narrow range (80-85% V̇O2peak). This range widens under heat stress, however, when exercise becomes protracted and a disassociation develops between relative exercise intensity, heart rate, and ratings of perceived exertion.
authors: Athlete Health and Performance Research Centre, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar julien.periard@aspetar.com.
authors: Julien D
authors: JD
authors: Périard
authors: Athlete Health and Performance Research Centre, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors: Sébastien
authors: S
authors: Racinais
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology*; D001642:Bicycling / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology; D003080:Cold Temperature; D016552:Ergometry; D015444:Exercise / Q000502:physiology*; D005260:Female; D005334:Fever / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D008297:Male; D010100:Oxygen / Q000097:blood*
chemical_list: D010100:Oxygen
keywords: V̇o2max; cardiovascular strain; cycling; fatigue; hyperthermia; pacing; thermoregulation; time trial