Skeletal muscle fibre size adaptation to an eight-week swimming programme

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Abstract
Summary To evaluate the effects of short-term physical training on muscle fibre size, seven males were submitted to an eight-week swimming programme. Biopsy samples from the triceps brachii muscle were obtained before and after the training period, and compared with controls. After training, free swimming maximal oxygen uptake was significantly higher in the exercised subjects (3.61 to 3.76 l·min−1), whereas the type I fibre distribution in the triceps was not affected (45.5 vs 44.6%). However, a significant increase in type II fibre area was observed (23.8%) and the type II/type I fibre area ratio increased from 1.63 to 1.83 with training. Muscle succinate dehydrogenase and phosphofructokinase activities were not significantly affected by the training programme. No significant changes were observed in the control group. It is concluded that type II fibres are recruited preferentially during a short-term swim-training programme.