by NSCA’s Sport and Exercise Nutrition, pg 151
Kinetic Select July 2019
The following is an exclusive excerpt from the book NSCA’s Guide to Sport and Exercise Nutrition, published by Human Kinetics. All text and images provided by Human Kinetics.
Carbohydrate loading is a practice used by athletes to saturate their endogenous stores of muscle glycogen before longer-duration events that typically lead to depletion of glycogen stores. Traditional carbohydrate loading studies conducted on untrained individuals incorporated a three- or four-day depletion phase in which athletes ingested a low-carbohydrate diet and completed a high volume of exercise training to “deplete” the internal stores of glycogen (Bergstrom and Hultman 1966). This phase was followed by a three- or four-day period of high carbohydrate ingestion (>70% carbohydrate or 8 to 10 g carbohydrate per kilogram body weight per day) and a decrease in exercise volume to facilitate supersaturation of muscle glycogen. Using this approach, early studies reported an ability of athletes to maintain their pace of training for significantly longer periods of time (Karlsson and Saltin 1971).
A series of studies in well-trained runners (Sherman et al. 1983, 1981) suggested that a reduction in exercise training volume along with a high-carbohydrate diet (65% to 70% dietary carbohydrate) over a minimum of three days can elevate muscle glycogen levels. These conclusions were well received as a much more practical approach to maximizing muscle glycogen. In eight trained runners, three days of a high-carbohydrate diet (10 g carbohydrate per kilogram body weight per day) while runners completely refrained from exercise maximized muscle glycogen stores (Bussau et al. 2002). Additionally, a high-carbohydrate (8.1 g carbohydrate per kilogram body weight per day or 600 g carbohydrate per day) diet significantly elevated preexercise glycogen stores versus a low-carbohydrate (1.4 g carbohydrate per kilogram body weight per day or 100 g carbohydrate per day) diet given to trained individuals for three days before completion of a 45-minute bicycle ride at 82% VO2peak.
Interestingly, a dose–response effect may be evident regarding the amount of carbohydrate that needs to be ingested when no depletion phase occurs to promote maximal levels of muscle glycogen. For example, baseline muscle glycogen was notably higher after ingestion of 10 g carbohydrate per kilogram body weight per day for one to three days when compared to ingesting 8 g/kg body weight per day for three days. Currently, this effect has not been investigated further, because initial carbohydrate loading studies that incorporated depletion phases and longer intakes of high carbohydrate reported higher levels of muscle glycogen (Bergstrom et al. 1967).
NSCA’s Guide to Sport and Exercise Nutrition will lead you through the key concepts of sport and exercise nutrition so that you can assess an individual’s nutrition status and—if it falls within your scope of practice—develop customized nutrition plans. The book is available in bookstores everywhere, as well as online at the NSCA Store.