Meeting Abstract
4.6 Saturday, Jan. 4 09:00 Architectural specialization of the forelimb musculature of the groundhog COPPLOE, JV*; RUPERT, JE; ROSE, JA; BUTCHER, MT; Youngstown State Univ.; Indiana Univ. School of Medicine; Youngstown State Univ.; Youngstown State Univ. jvcopploe@student.ysu.edu
Scratch-digging animals are commonly described as having large, powerful forelimb muscles for applying high out-force to excavate earth, yet studies quantifying the architectural properties of the musculature are largely unavailable. Our previous work with semi-fossorial badgers identified several features of forelimb muscle design that may represent specializations for scratch-digging. To further test hypotheses about which of these traits is a specialization versus a feature common to the forelimbs of digging mammals, we quantified muscle architectural properties in the forelimb of the groundhog (Marmota monax), a generalist burrower that constructs semi-complex burrows. Architectural properties measured were muscle moment arm, muscle mass (MM), belly length (ML), fascicle length (FL), pennation angle, and physiological cross-sectional area (PCSA), and these metrics were used to estimate maximum isometric force, joint torque, and power. Groundhogs possess large humeral retractors and elbow extensors that are capable of applying moderate torques at the shoulder and elbow joints. Most of these muscles have high FL:ML ratios, indicating substantial shortening ability for high power generation. The carpal and digital flexors show relatively greater pennation and shorter fascicles lengths than the humeral retractors and elbow extensors, and thus have higher PCSA:MM ratios and force production capacity. Moreover, the carpal/digital flexors have the capacity for both shortening and force indicating high work and power potential. Overall, the muscle properties found may be common across digging mammals, whereas more complex elbow extensors with the ability to apply much higher torque and power at the shoulder joint may represent specializations for fossorial habit.
