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Weight-lifters, endurance events athletes and untrained controls (8 in each group) were studied by means of muscle biopsy, and determination of maximal aerobic capacity and maximal voluntary isometric muscle strength. By histochemical methods applied to the biopsy specimens, muscle fibres were separated in two main groups: red fibres (with low activity of myofibrillar ATPase) and white fibres (with high activity of myofibrillar ATPase). The weight lifters with high isometric muscular strength had significantly larger white fibres than the others. The endurance events athletes with high aerobic capacity but ordinary isometric muscle strength had white fibres of the same size as the control group. The size of the red fibres was the same for all three groups. It was concluded that a high isometric muscular strength is well correlated with large cross-sectional area of white fibres. The size of red fibres seems to be unrelated to isometric muscular strength as well as aerobic capacity.
Edström et al. (Sat,) studied this question.