Does the anatomical location of a muscle affect the influence of undernutrition on muscle fibre number?

Nutritional restriction during muscle fibre number development invariably has a more detrimental effect on the biceps brachii than on the soleus. The difference may be due to the relative proportions of fibre types in the muscles or the anatomical location of the muscles. To distinguish between the effects of location and fibre type the biceps (fast, cranial and proximal), soleus (slow, caudal and distal), and extensor digitorum longus (EDL) (fast, caudal and distal) were examined from control and undernourished guinea pig neonates. A 40% reduction in maternal intake resulted in a reduction in neonate body and muscle weights (P < 0.005), biceps (P < 0.05) and EDL fibre numbers (P < 0.005), but did not affect soleus fibre number. At birth the ratio of fast fibres to slow was 7.5 for the biceps, 7.0 for the EDL, and 1.5 for the soleus. The effect of undernutrition on muscle fibre number therefore seems to be a function of the fibre types in that muscle.