MCGUIGAN, M.P.*; LEE, D.V.; YOO, E.H.; BIEWENER, A.A.; Harvard University; Harvard University; Harvard University; Harvard University: Proximal hindlimb muscle strain and activation patterns in jumping goats

Terrestrial animals are required to move over a variety of different terrains in their natural habitat. Goats are non specialist locomotors who are very proficient runners, jumpers and climbers, but how do their limb muscles adapt to these different mechanical tasks? In this study we investigated the role of biceps femoris (hip extensor) and vastus lateralis (knee extensor) during jumping. These are both major hindlimb extensor muscles that would be expected to do work to raise the centre of mass during take off and to absorb energy during landing. A 65cm platform was placed adjacent to a series of two forceplates, and ground reaction forces and 3D kinematics were recorded while the goats jumped onto and off the platform. Simultaneous sonomicrometry and electromyography signals were recorded to explore fascicle length change and activation in vastus lateralis and the superior and inferior portions of biceps femoris. Three sonomicrometry crystals were used in each region of biceps femoris to assess fascicle strain heterogeneity. During take off vastus lateralis exhibited a stretch-shorten cycle as the knee flexed and then extended, with a net shortening of 6-14%. Biceps femoris generally shortened throughout stance exhibiting a net shortening of 25-35%. There was however, a degree of strain heterogeneity in the superior region: the distal part of the fascicle straining considerably (7-18%) less than the proximal part (32-35%). Although the majority of the negative work would be expected to be performed by the forelimb during landing, both muscles exhibited net lengthening during the landing stance: 8-12% in vastus lateralis and 5-16% in biceps femoris. These results suggest that both muscles perform work during take off and absorb energy on landing. This work was supported by NIH grant R01-AR047679 to A.A.B.