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Effect of carbohydrate ingestion and ambient temperature on muscle fatigue development in endurance-trained male cyclists

¹School of Exercise, Biomedical and Health Sciences, Edith Cowan University, Joondalup, Western Australia; ²School of Human Movement Studies, University of Queensland, Brisbane, Queensland, Australia; ³Consolidated Research Institute for Advanced Science and Medical Care, Waseda University, Tokyo, Japan; and ⁴Department of Physiology, Australian Institute of Sport, Canberra, Australian Capital Territory, Australia

Submitted 26 June 2007 ; accepted in final form 16 January 2008

The aim of the present study was to determine the effect of carbohydrate (CHO; sucrose) ingestion and environmental heat on the development of fatigue and the distribution of power output during a 16.1-km cycling time trial. Ten male cyclists (O_2max = 61.7 ± 5.0 ml·kg^–1·min^–1, mean ± SD) performed four 90-min constant-pace cycling trials at 80% of second ventilatory threshold (220 ± 12 W). Trials were conducted in temperate (18.1 ± 0.4°C) or hot (32.2 ± 0.7°C) conditions during which subjects ingested either CHO (0.96 g·kg^–1·h^–1) or placebo (PLA) gels. All trials were followed by a 16.1-km time trial. Before and immediately after exercise, percent muscle activation was determined using superimposed electrical stimulation. Power output, integrated electromyography (iEMG) of vastus lateralis, rectal temperature, and skin temperature were recorded throughout the trial. Percent muscle activation significantly declined during the CHO and PLA trials in hot (6.0 and 6.9%, respectively) but not temperate conditions (1.9 and 2.2%, respectively). The decline in power output during the first 6 km was significantly greater during exercise in the heat. iEMG correlated significantly with power output during the CHO trials in hot and temperate conditions (r = 0.93 and 0.73; P < 0.05) but not during either PLA trial. In conclusion, cyclists tended to self-select an aggressive pacing strategy (initial high intensity) in the heat.

power; integrated electromyography; heat; thermoregulation