Abstract

The relationships between muscle fibre characteristics and the physical performance capacity of trained athletic boys (11-13 y) were studied over 2 days. The subjects were divided into two groups according to muscle fibre distribution. The fast group (FG) comprised 10 subjects (sprinters, weightlifters, tennis players) with more than 50 fast-twitch fibres (type II), and the slow group (SG) comprised 8 subjects (endurance runners, tennis players, one weightlifter) with more than 50 slow-twitch fibres (type I) in their vastus lateralis muscle. The fast group had 59.2 +/- 6.3 and the slow group had 39.4 +/- 9.8 type II fibres. Other clear differences between the groups were observed as regards reaction time, rate of force development and rise of the bodys centre of gravity in the squatting jump. For these variables, the fast group was superior to the slow group. Muscle fibre distribution ( type II) correlated negatively with reaction time. Muscle fibre area ( type II) correlated negatively with reaction time and positively with chronological age height, mass, serum testosterone, force production and blood lactate in the 60-s maximal anaerobic test. There were no significant correlations between muscle fibre characteristics and maximal oxygen uptake. The present study assumes that heredity partly affects the selection of sporting event. Growth, development and training are associated with muscle fibre area, which affects the physical performance capacity of the neuromuscular system in trained young boys. Verf.-Referat