Journal of Applied Physiology
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J Appl Physiol 97: 1245-1253, 2004. First published May 21, 2004; doi:10.1152/japplphysiol.01368.2003
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Effects of carbohydrate supplementation on performance and carbohydrate oxidation after intensified cycling training

Shona L. Halson,1,2 Graeme I. Lancaster,1 Juul Achten,1 Michael Gleeson,1 and Asker E. Jeukendrup1

1Human Performance Laboratory, School of Sport and Exercise Sciences, University of Birmingham, Edgbaston B15 2TT, United Kingdom; 2School of Human Movement Studies, Queensland University of Technology, Kelvin Grove, Queensland 4059, Australia

Submitted 22 December 2003 ; accepted in final form 6 May 2004

To study the effects of carbohydrate (CHO) supplementation on performance changes and symptoms of overreaching, six male endurance cyclists completed 1 wk of normal (N), 8 days of intensified (ITP), and 2 wk of recovery training (R) on two occasions in a randomized crossover design. Subjects completed one trial with a 6% CHO solution provided before and during training and a 20% solution in the 1 h postexercise (H-CHO trial). On the other occasion, subjects consumed a 2% CHO solution at the same time points (L-CHO). A significant decline in time to fatigue at ~63% maximal power output (H-CHO: 17 ± 3%; L-CHO: 26 ± 7%) and a significant increase in mood disturbance occurred in both trials after ITP. The decline in performance was significantly greater in the L-CHO trial. After ITP, a significant decrease in estimated muscle glycogen oxidation (H-CHO: N 49.3 ± 2.9 kcal/30 min, ITP 32.6 ± 3.4 kcal/30 min; L-CHO: N 49.1 ± 30 kcal/30 min, ITP 39.0 ± 5.6 kcal/30 min) and increase in fat oxidation (H-CHO: N 16.3 ± 2.4 kcal/30 min, ITP 27.8 ± 2.3 kcal/30 min; L-CHO: N 16.9 ± 2.6 kcal/30 min, ITP: 25.4 ± 3.5 kcal/30 min) occurred alongside significant increases in glycerol and free fatty acids and decreases in free triglycerides in both trials. An interaction effect was observed for submaximal plasma concentrations of cortisol and epinephrine, with significantly greater reductions in these stress hormones in L-CHO compared with H-CHO after ITP. These findings suggest that CHO supplementation can reduce the symptoms of overreaching but cannot prevent its development. Decreased endocrine responsiveness to exercise may be implicated in the decreased performance and increased mood disturbance characteristic of overreaching.

overreaching; metabolism; stable isotope


Address for reprint requests and other correspondence: S. L. Halson, Dept. of Physiology, Australian Institute of Sport, PO Box 176, Belconnen ACT, Australia 2616 (E-mail: shona.halson{at}ausport.gov.au).






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