Glycogen Utilization in Wheelchair-Dependent Athletes*

Seven wheelchair-dependent endurance athletes (5 males, 2 females, mean age = 27 years, mean VO2 max = 2.01 1/min) consented to maximal and submaximal (SM) testing on a wheelchair ergometer for the purpose of determining aerobic capacity, plasma substrate concentration, and muscle glycogen utilization during prolonged exercise. Results from an initial graded maximal test were used to determine exercise intensity levels during a subsequent 1-h submaximal endurance ride on the wheelchair ergometer (60%-70% VO2 max). Muscle biopsy samples (N = 5) were taken from the M. deltoideus (anterior head) before and after the submaximal exercise. Hematocrit (Hct), hemoglobin (Hb), glycerol (G), glucose (Glu), and free fatty acids (FFA) measured from venous blood taken before, midway, and at completion of the SM test demonstrated changes in plasma volume and substrate level similar to those of other athletes observed while running on a treadmill or exercising on a cycle ergometer. Type I fibers were characteristically depleted of glycogen, as measured by PAS stain, as a result of the SM endurance ride. Pre-exercise glycogen values were similar among subjects (means = 92.46 mmol X kg-1 +/- SEM 1.8) while muscle glycogen utilization varied from 17.4 to 46.6 mmol X kg-1. These findings indicate that physiologic response patterns of the upper arm muscles of trained wheelchair athletes during acute endurance exercise correspond to those observed in the leg muscles of able-bodied endurance athletes.