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Fluid Replacement and Heat Stress, 1993

Pp. 99-110. Washington, D.C.

National Academy Press

8

Timing of Carbohydrate Supplementation During Prolonged Strenuous Exercise

Edward F. Coyle1and Andrew R. Coggan

INTRODUCTION

Both muscle glycogen and plasma glucose are oxidized by skeletal muscle to supply energy during prolonged exercise (Ahlborg and Felig, 1982; Ahlborg et al., 1974; Bergstrom and Hultman, 1966, 1967; Gollnick et al., 1981; Hermansen et al., 1967; Ivy et al., 1983; Pallikarakis et al., 1986; Pirnay et al., 1982; Wahren, 1970). Although the underlying mechanisms are uncertain, there appears to be a gradual shift from intramuscular glycogen toward blood-borne glucose as the predominant carbohydrate energy source as exercise proceeds and as muscle glycogen is depleted (Coggan and Coyle, 1987; Coyle et al., 1986; Gollnick et al., 1981; Ivy et al., 1983; Wahren, 1970). The contribution of glucose to oxidative metabolism may be limited, however, by a decline in the plasma glucose concentration late in exercise as liver glycogen stores diminish. Therefore, it may be necessary to ingest carbohydrate to maintain or elevate the blood glucose concentration. We

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Edward F. Coyle, The Human Performance Laboratory, The University of Texas at Austin, Austin, TX 78712



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