Meeting Abstract

42.1  Jan. 6  Function of uniarticular and biarticular heads of the triceps during jumping and landing in goats. CARROLL, A. M.*; BIEWENER, A. A.; Concord Field Station, Harvard University; Concord Field Station, Harvard University acarroll@oeb.harvard.edu

Muscle systems in the limbs of tetrapods are often organized into synergistic uni- and bi-articular regions. To understand how these regions might differ in their function, we investigated the function of the long (biarticular) and lateral (uniarticular) heads of the triceps muscle of four goats (25-43 Kg) during jumping and landing. EMG electrodes were used to measure muscle depolarization, sonomicrometry crystals were used to measure muscle strain, and inverse dynamics (based on simultaneous video, force plate recordings, and limb data) were used to estimate elbow moments and (by assuming equal stress) muscle force. Forelimb use during landing was symmetrical, but during jumping it was either be symmetrical (two bounding legs) or asymmetrical with separate leading and lagging legs. In all jumping and landing conditions the elbow was compressed in the onset of stance and extended later in stance. During the compression phase the lateral head was always stretched, while the long head was stretched only in landing. Both heads shortened during re-extension. During landing both heads functioned to absorb work and power, and more net work and power was absorbed in the lateral head. In all jumping conditions, the long head produced more total work and power than the lateral head which only produced net positive work and power in the leading jumps. Elbow moment and muscle stress were greatest in the leading leg of asymmetrical jumps, and were lowest in the lagging leg and during landing conditions. In general, biarticularity allows the long head to shorten throughout stance while strain in the lateral head is tightly tied to elbow kinematics. This research was supported by NIH grant AR-047679 to Andrew A. Biewener.