Functional specialization in the intrinsic forelimb musculature of the American badger (Taxidea taxus)

Abstract

Evaluation of relationships between muscle structure and digging function in fossorial species are lacking. We quantified muscle architecture in the forelimbs of American badgers (Taxidea taxus) and estimated force, power, and joint torque of their intrinsic musculature as these functional properties relate to their scratch-digging behavior. For comparison with the badger, muscle properties of the generalist opossum (Didelphis virginiana) were also quantified. Architectural properties measured included: muscle mass, length, volume, physiological cross-sectional area, fascicle length and pennation angle. Badgers showed significantly more massive shoulder flexors, elbow extensors and digital flexors. The triceps brachii for badger was the most massive muscle group studied and displayed long fascicles with little pennation, an architecture consistent with appreciable shortening capability and higher power. In addition to elbow extension, uniquely two biarticular heads (long and medial) of the triceps are capable of applying large flexor torques to the shoulder to retract the forelimb throughout the power stroke. The massive and complex digital flexors showed relatively greater pennation and shorter fascicle lengths in addition to compartmentalization of muscle heads for both force production and range of shortening to flex the carpus and digits. Muscles in other functional groups with short muscle moment arms showed some specialization for high force production, and are likely important for resistance against high limb forces imposed by interaction of the forelimb with the substrate. Collectively, the muscle specializations observed for badger indicate important differences between the forelimbs of fossorial and non-fossorial species, and indicate mechanisms for application of large out-forces during scratch-digging in badgers.