Submitted on December 22, 2003
Accepted on May 6, 2004
Effect of carbohydrate supplementation on performance and carbohydrate oxidation following intensified cycling training
Shona L Halson1, Graeme I Lancaster2, Juul Achten2, Michael Gleeson2, and Asker E Jeukendrup2*
1 Human Performance Laboratory, Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom; School of Human Movement Studies, Queensland University of Technology, Brisbane, Queensland, Australia
2 Human Performance Laboratory, Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
* To whom correspondence should be addressed. E-mail: a.e.jeukendrup{at}bham.ac.uk.
To study the effects of carbohydrate (CHO) supplementation on performance changes and symptoms of overreaching, six male endurance cyclists completed one week of normal (N), eight days of intensified (ITP) and two weeks of recovery training (R) on two occasions in a randomized cross-over design. Subjects completed one trial with a 6% CHO solution provided before and during training and a 20% solution in the one hour post exercise (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% Wmax (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±2.9kcal/30min: ITP: 32.6±3.4 kcal/30min; L-CHO: N: 49.1±30. kcal/30min: ITP: 39.0±5.6 kcal/30min) and increase in fat oxidation (H-CHO: N: 16.3±2.4 kcal/30min: ITP: 27.8±2.3 kcal/30min; L-CHO: N: 16.9±2.6 kcal/30min: ITP: 25.4±3.5 kcal/30min) 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, prolactin and adrenaline, with significantly greater reductions in these stress hormones in L-CHO when compared to H-CHO after ITP. These findings suggest that carbohydrate 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.
