Overtraining and glycogen depletion hypothesis. Med. Sci. Sports Exerc., Vol. 30, No. 7, pp. 1146-1150, 1998. Low muscle glycogen levels due to consecutive days of extensive exercise have been shown to cause fatigue and thus decrements in performance. Low muscle glycogen levels could also lead to oxidation of the branched chain amino acids and central fatigue. Therefore, the questions become, can low muscle glycogen not only lead to peripheral and central fatigue but also to overtraining, and if so, can overtraining be avoided by consuming sufficient quantities of carbohydrates? Research on swimmers has shown that those who were nonresponsive to an increase in their training load had low levels of muscle glycogen and consumed insufficient energy and carbohydrates. However, cyclists who increased their training load for 2 wk but also increased carbohydrate intake to maintain muscle glycogen levels still met the criteria of over-reaching (short-term overtraining) and might have met the criteria for overtraining had the subjects been followed for a longer period of time. Thus, some other mechanism than reduced muscle glycogen levels must be responsible for the development and occurrence of overtraining.
Department of Human Kinetics, University of Wisconsin-Milwaukee, Milwaukee, WI 53201
Submitted for publication October 1997.
Accepted for publication November 1997.
The author extends her appreciation to Harm Kuipers, Carl Foster, Bo Cheng, Asker Jeukendrup, Mattius Hesselink, Rodrique Servais, and Erik Fransen, all of whom were colleagues during the investigations reported in this paper.
Address for correspondence: Ann C. Snyder, Ph.D., Department of Human Kinetics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201. E-mail:firstname.lastname@example.org.
Ann C. Snyder was a Fulbright Scholar at the University of Maastricht during some of the reported investigations.