Why is the gracilis muscle relatively uninvolved in neuromuscular disorders?

CT scanning of thigh muscles has shown that the gracilis is often relatively resistant to degeneration in neuromuscular disorders. We have compared the histometric features of the gracilis muscle with the biceps femoris and vastus lateralis muscles in the right and left thighs of 12 subjects without neuromuscular disease. There was striking variation between individuals, but marked similarities between the two limbs in individuals. The gracilis and vastus lateralis muscles contained fewer Type 1 fibres than the biceps femoris. The Type 2 fibres were slightly larger in vastus lateralis than in the other two muscles. There is thus no evident morphological difference between the gracilis muscle and other thigh muscles that can be correlated with the different susceptibility of these muscles in neuromuscular diseases. However, these muscles are subject to differing physiological stresses in movement, and these may be important in determining the response to disease.