IN-SERIES FIBER ARCHITECTURE IN LONG HUMAN MUSCLES

The fiber architecture of adult human sartorius and gracilis muscles w as examined using a combination of fiber microdissections and histolog ical methods. Intact fibers were dissected from fascicles of muscle st rips that were digested in nitric acid. All of these fibers terminate intrafascicularly by tapering to a fine strand at one or both ends. Th ey measure 4-20 cm after correction for shrinkage. Systematic dissecti ons of 1 cm long blocks sampled at intervals along the muscle length s uggest that tapered fiber endings occur at all locations along the mus cle but are most common centrally; here they accounted for up to 14% o f dissected fibers in each block. Transverse sections of muscle confir m that fiber profiles with small diameters occur at all levels of the muscle but are especially common in sections more than 5 cm from its o rigin or insertion. The architectural arrangement demonstrated here su ggests that long human muscles, like muscles in other species, are com posed of relatively short, in-series fibers. This has many implication s for the neural activation and force-developing behavior of these mus cles that must be considered when paralyzed muscles are reanimated usi ng electrical stimulation. Further, it may predispose long muscles to certain types of neuromuscular damage and dysfunction.