Relationships between muscle fibre characteristics and physical performance capacity in trained athletic boys

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Abstract
The relationships between muscle fibre characteristics and the physical performance capacity of trained athletic boys (aged 11–13 years) 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 (P <0.05–0.01) between the groups were observed as regards reaction time, rate of force development and rise of the body's 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 (P P <0.05–0.001) and positively with chronological age (P P P P P <0.05–0.01) and blood lactate (P 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.