Muscle Glycogen Utilization and the Expression of Relative Exercise Intensity

Abstract

Previous research has shown that the rate of muscle glycogen utilization is related to exercise intensity expressed relative to maximal aerobic power (%VO2max). The purpose of this study was to compare the relationship between glycogen utilization and %VO2max to that between glycogen utilization and intensity expressed relative to the onset of blood lactate accumulation (%OBLA) during cycle exercise. It was hypothesized that the rate of glycogen utilization would be related more closely to intensity expressed as %OBLA than to intensity expressed as %VO2max. Nineteen subjects (15 males and 4 females) performed two separate tests to determine VO2max and OBLA during continuous incremental exercise. On a third occasion biopsies were taken from the m. vastus lateralis before and after 30 min of exercise at randomly assigned intensities ranging from 50-80% VO2max, corresponding to 67-117% OBLA. There was a large inter-subject variation in aerobic fitness with VO2max ranging from 34 to 66 mL.kg-1.min-1 and OBLA ranging from 64-84% VO2max. Absolute VO2max and the VO2 at OBLA were correlated strongly (r = 0.90). The change in glycogen concentration during the 30-min exercise bout ranged from an increase of 58 to a depletion of 200 mmol glucose units.kg-1 dry muscle weight. Neither absolute nor relative glycogen utilization was significantly related to the exercise intensity expressed as either %VO2max or %OBLA. Stepwise multiple regression was used to identify variables which could account for the variation in glycogen depletion.(ABSTRACT TRUNCATED AT 250 WORDS)