Effect of low nutrition on size of striated muscle fibres in the mouse

Inbred, male 129/Re mice were maintained on a low plane of nutrition for a period of 21 days. After this time they were sacrificed and the following five muscles were examined for total fibre number and fibre diameter distributions, anterior tibialis, biceps brachii, extensor digitorum longus, soleus and sternomastoideus. Changes in body weight and muscle weight were also recorded. The low plane of nutrition resulted in a significant body weight loss (30%) and variously decreased muscle weights. The ratios, muscle weight: body weight, however, were higher in the experimental mice. The total fibre numbers of the muscles were not affected by the plane of nutrition. The mean fibre diameters of all the muscles, except the soleus, were lower in the experimental mice. These lower values were brought about by a decrease in the proportions of fibres of large diameter and not by the reduction in diameter of all the fibres. It was concluded that a low plane of nutrition caused fat deposits to be depleted, thereby reducing the body weight and the work‐load of the phasic muscles, i.e., muscles bringing about body movements. This enabled the muscles to be effective at a smaller size. The level of muscle growth was adjusted at the individual fibre level.