Skeletal muscle enzyme activity, fiber composition and $$\dot V$$ O2 max in relation to distance running performance

Abstract

Muscle biopsy samples were obtained from the gastrocnemius of 26 well-trained runners of widely varying ability. Portions of the sample were analyzed for succinate dehydrogenase (SDH) activity and for muscle fiber composition. \(\dot V\)O₂ max was determined during uphill treadmill running. Mean values for muscle SDH activity (14.6 U/g), fiber composition (55% slow twitch) and \(\dot V\)O₂ max (60.9 ml/kg×min⁻¹) were lower than reported previously for groups of elite and sub-elite runners. The physiological data were consistent with the performance ability of the sample [5∶12, 11∶20 and 36∶40 (min∶s) for 1, 2 and 6 miles, respectively]. Within the sample, performance was most strongly related to \(\dot V\)O₂ max (r=−0.84, −0.87 and −0.88 for 1, 2, and 6 miles). There was little relationship between muscle SDH activity and either performance (r=−0.11, −0.14, −0.20 for 1, 2, and 6 miles) or \(\dot V\)O₂ max (r=0.23). The relationship between muscle fiber composition and performance was only modestly strong (r=−0.52, −0.54, −0.55 for 1, 2, and 6 miles). The results indicate that the primary determinant of cross-sectional differences in running performance is \(\dot V\)O₂ max. Skeletal muscle metabolism apparently contributes little to these cross-sectional differences and may be of much greater importance to variations in performance within an individual.