Heredity and muscle adaptation to endurance training

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Abstract
HAMEL, P., J.-A. SIMONEAU, G. LORTIE, M. R. BOULAY, and C. BOUCHARD. Heredity and muscle adaptation to endurance training. Med. Sci. Sports Exerc., Vol. 18, No. 6, pp. 690–696, 1986. To determine whether sensitivity of muscle characteristics and aerobic performances to endurance training was genotype-dependent, 6 pairs of monozygotic (MZ) twins, 21 ± 4 yr of age (mean ± SD), took part in a 15-wk ergocycle endurance training program. Tests were performed before and after 7 and 15 weeks of training. A biopsy of the vastus laterulis muscle was obtained for the determination of fiber type composition and activities of creatine kinase, hexokinase, phosphofructokinasc, lactate dehydrogenase, malate dehydrogenase, 3-hydroxyacyl CoA dehydrogenase, and oxoglutarate dehydrogenase. Maximal oxygen uptake was measured with a progressive maximal ergocycle test, while endurance performance was determined as the total work output during a 90-min maximal ergocycle test. Results indicated that maximal oxygen uptake.kg-1 and endurance performance.kg-1 increased significantly (14 and 31%, respectively) with training, and intra-pair resemblance (intra-class) in response to 15 wk of training ranged from 0.65 to 0.83. Hexokinase (31%), phosphofructokinase (37%), lactate dehydrogenase (21%), malate dehydrogenase (31%), and 3-hydroxyacyl CoA dehydrogenase (60%) were significantly increased with training whereas no mean change in fiber-type proportions, oxoglutarate dehydrogenase and creatine kinase activities and the phosphofructokinase/oxoglutarate dehydrogenase ratio was observed. Similarity within twin pairs in the response to enzyme activities was mainly detected in the second half of the training program. The present results confirm, therefore, that both maximal oxygen uptake and endurance performance responses to training are largely genotype-dependent. Similarity within twin pairs in the response to enzyme activities was low in the first 7 wk of endurance training, but upon exposure to an additional 8 wk of training, muscle enzyme adaptation became generally more closely associated with the genotype.