Anatomical, architectural, and biochemical diversity of the murine forelimb muscles.

We characterized the architecture, fiber type, titin isoform distribution, and collagen content of 27 portions of 22 muscles in the murine forelimb. The mouse forelimb was different from the human arm in that it had the extensor digitorum lateralis muscle and no brachioradialis muscle. Architecturally, the mouse forelimb differed from humans with regard to load bearing, having a much larger contribution from extensors than flexors. In mice, the extensor : flexor PCSA ratio is 2.7, whereas in humans it is only 1.4. When the architectural difference index was calculated, similarities became especially apparent between flexors and extensors of the distal forelimb, as well as pronators. Discriminant analysis revealed that biochemical measures of collagen, titin, and myosin heavy chain were all strong between-species discriminators. In terms of composition, when compared with similar muscles in humans, mice had, on average, faster muscles with higher collagen content and larger titin isoforms. This report establishes the anatomical and biochemical properties of mouse forelimb muscles. Given the prevalence of this species in biological studies, these data will be invaluable for studying the biological basis of mouse muscle structure and function.