John O. Holloszy, Wendy M. Kohrt and Polly A. Hansen

Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, USA

Received 9/2/98 Accepted 9/8/98

2. INTRODUCTION

Blood glucose and muscle glycogen are essential for prolonged, strenuous exercise. The rate of carbohydrate utilization during prolonged exercise is closely geared to the energy needs of the working muscles. In contrast, fat utilization during exercise is not tightly regulated, as there are no mechanisms for closely matching the availability and metabolism of fatty acids to the rate of energy expenditure. As a consequence, the rate of fat oxidation during exercise is determined by the rate of carbohydrate utilization and by the availability of fatty acids. The primary role of fat during vigorous exercise in humans and rodents is to spare blood glucose (i.e. liver glycogen) and muscle glycogen.

This review focuses on the regulation of carbohydrate metabolism during and after exercise and its interaction with fat metabolism. It deals primarily with studies on humans and rats. Many elegant studies have been performed on the regulation of substrate metabolism during exercise in dogs, and the large literature on this subject has been reviewed by others (1,2).