[The adaptation of human skeletal muscle fibers during aerobic training]

Effect of training on dimensions of muscle fibres of fast twitch and slow-twitch types were studied in three groups of subjects: local training of m. triceps surae (volunteers) in laboratory conditions, training of amateur joggers and of elite racers--skiers. Significant negative correlations between initial level and training-induced changes of muscle fibre cross sectional areas were demonstrated. The correlations found indicate that muscle fibre dimensions of people using similar endurance training programme tend to some certain level which is likely to be the optimal for this type of training. Dimensions of muscle fibre may significantly change as the result of traiining, probably, only in the case, when their initial values differ from the optimal one.