Submitted on June 26, 2007
Accepted on January 16, 2008
Effect of carbohydrate ingestion and ambient temperature on muscle fatigue development in endurance-trained male cyclists
Chris R. Abbiss1*, Jeremiah J. Peiffer1, Jonathan Michael Peake2, Kazunori Nosaka1, Katsuhiko Suzuki3, David T. Martin4, and Paul B. Laursen1
1 School of Exercise, Biomedical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, Australia
2 School of Human Movement Studies, University of Queensland, Brisbane, Queensland, Australia
3 Consolidated Research Institute for Advanced Science and Medical Care, Waseda University, Tokyo, Japan
4 Physiology, Australian Institute of Sport, Belconnen ACT, Australia
* To whom correspondence should be addressed. E-mail: c.abbiss{at}ecu.edu.au.
The aim of the present study was to determine the effect of carbohydrate (sucrose) ingestion (CHO) 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 (mean ± SD; VO2max = 61.7 ± 5.0 ml·kg-1·min-1) 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 oC) or hot (32.2 ± 0.7 oC) 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. Prior to and immediately following exercise, percent muscle activation was determined using superimposed electrical stimulation. Power output, integrated electromyography (iEMG) of vastus lateralis, rectal temperature and skin temperatures were recorded throughout the trial. Percent muscle activation significantly declined during the CHO and PLA trials in hot (6.0 and 6.9%) 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.
