The effect of nutrition on the size and proportion of muscle fibre types during growth.

To investigate whether the retardation in the increase of body weight produced by reduced food intake could influence the transformation of muscle fibre types in soleus and extensor digitorum longus (EDL) during growth, rats were divided into 3 groups at 3 wk of age. Each group was subjected to food restriction from 3 wk of age to the following ages. Group 1 comprised 5 (148.7 +/- 7.3 g), 7 (250.7 +/- 11.1 g), 9 (362.9 +/- 19.3 g) and 11-wk-old rats (414.9 +/- 35.2 g) fed ad libitum. Group 2 comprised 5 (148.7 +/- 7.3 g), 7 (148.6 +/- 7.7 g), 9 (147.7 +/- 6.0 g) and 11-wk-old rats (148.8 +/- 5.7 g) fed a restricted diet; these animals were similar in weight to the 5-wk-old rats in group 1. Group 3 comprised 4 subgroups of 11-wk-old rats (148.7 +/- 5.7 g, 247.6 +/- 6.8 g, 354.4 +/- 8.6 g, 414.4 +/- 35.2 g); their body weights were adjusted to the weights of 5, 7, 9 and 11-wk-old rats in group 1 by restriction of food intake. Muscle weights and fibre areas in soleus and EDL significantly increased with growth. The muscle weights and fibre areas in group 2 in which body weights were equal increased significantly with age, but the increases were significantly less than for group 1. The muscle weights and fibre areas in group 3 in which ages were equal increased significantly with increasing body weight; the increases were the same as those in group 1.(ABSTRACT TRUNCATED AT 250 WORDS)