Ultrastructure and biochemical function of skeletal muscle in twins

Muscle biopsies were obtained from eleven pairs of monozygotic and six pairs of dizygotic twins, and maximum oxygen consumption (Vo2) was measured. There were no differences between the two groups of twins in their intra-pair variation, except for two enzyme systems, glyceraldehyde-3P-dehydrogenase (GAPDH) and 3-hydroxyacyl-CoA-dehydrogenase (HAD). The effects of training were assessed by comparing the differences between twins when one member of each pair undertook a 23 week training programme. There were significant differences in VO2 max, heart volume and maximum oxygen pulse after training, and some significant cytological differences. It was concluded that environmental factors were stronger than genetic influences, as far as physical performance was concerned.