Meeting Abstract

40.4  Friday, Jan. 4  Effects of speed on muscle function of the triceps brachii in goats CARROLL, Andrew M.*; BIEWENER, Andrew A.; Concord Field Station, Harvard University; Concord Field Station, Harvard University acarroll@oeb.harvard.edu

Distal limb muscles primarily function to generate force in steady running, allowing tendons to absorb and return work. Proximal limb muscles tend to relatively short tendons, which may require muscle fascicles to absorb or produce joint work, thus increasing the metabolic cost of locomotion. A specific understanding of how proximal muscles function in vivo, and how that function varies with speed, is necessary to analyze cursorial locomotor anatomy and to evaluate the limits of locomotor performance. In this study the roles of two proximal forelimb muscles, the biarticular long head and monarticular lateral heads of the triceps brachii of goats (25-43 kg), were compared to understand how their different anatomies might result in differential muscle function across changes in locomotor speed (1-5 m s^-1). Muscle strain was measured by sonomicrometry, while skeletal kinematics were recorded with high-speed video. The monoarticular lateral head stretched with elbow flexion and shortened with elbow extension, while the long head shortened throughout stance. Magnitude of stretch in the lateral head increased with speed (r²=0.37; p<0.0001), as did rate (r2=0.55; p<0.0001). Magnitude of shortening in the lateral head did not increase with speed, but the rate of shortening increased significantly in all individuals (r²=0.44; p<0.0001). Magnitude of shortening in the long head did not change with speed in all animals, but fascicle shortening speed increased consistently with consistently with locomotor speed (r²=0.57; p<0.0001). These patterns support a general dichotomy in proximal muscle function between work producing and work absorbing stance-phase muscles. This research was supported by NIH grant AR-047679 to Andrew A. Biewener.