Does skeletal muscle fiber branching play a role in the inability of old EDL dystrophic muscle to resist large passive stretches?

摘要

Hakim et al. (3) examined the passive mechanical properties of fast-twitch extensor digitorum longus (EDL) muscles from young and old mdx dystrophic mice. They elegantly showed that by increasing passive strain on the dystrophic muscle from 110% of optimal length (Lo) to 160% of Lo, the muscle physically ruptured in a manner that got progressively worse with age. At the oldest age points tested, 14 and 20 mo, the dystrophic muscles pulled apart. Importantly, in age matched dystrophin positive controls, this pulling apart of the muscle did not occur. The authors (3) propose that one reason for this dramatic tearing of the dystrophic muscle with age is due to increased fibrosis and muscle stiffness. Undoubtedly, increasing stiffness with age would play a role in dystrophic damage. However, I suggest that the widely reported age-related increase in the number of branched skeletal muscle fibers present within the dystrophic muscle will also make a significant contribution (1,2,4-6).