Meeting Abstract
82.5 Sunday, Jan. 6 Influence of tendon compliance and activation level on fibre operating lengths of skeletal muscle RUBENSON, J.*; SANGHVI, H.; CROMIE, M.J.; EASTON, K.; MARSH, R.L.; DELP, S.L.; Univ. of W. Australia; Linkoping Univ.; Stanford Univ.; Univ. of W. Australia; Northeastern Univ.; Stanford Univ. Jonas.Rubenson@uwa.edu.au
The region over which skeletal muscles operate on their force-length (F-L) curve is fundamental to the mechanics of movement. Function at the plateau region of the F-L curve may be regarded as favourable since force capacity is optimized. The activation level (ACT) of a muscle will, to a large extent, dictate its force output and in turn will affect tendon stretch and muscle fibre lengths. It remains possible that muscle-tendon units with high tendon compliance have a restricted range of ACT over which optimal fibre lengths can be achieved compared to muscles with low tendon compliance. To test this question we developed a three-dimensional (3D) musculoskeletal model of the guinea fowl hind limb that included 3D bone geometry, muscle-tendon paths and wrapping surfaces, and muscle-tendon architecture properties including muscle PCSA, optimal fibre lengths and tendon stiffness. We simulated the region of the F-L curve occupied by the lower-limb muscles under 4 ACT conditions: 1) 100% ACT (maximal), 2) 50% ACT, 3) 25% ACT and 4) 0% ACT (passive). We found that muscle-tendon units with low tendon compliance (hip muscles) have a length operating range that is largely insensitive to ACT. On the other hand, muscles with high tendon compliance (lower limb muscles with long external tendons) have a length operating range that is highly sensitive to ACT. Interestingly, certain muscles (gastrocnemius) operate across the plateau region of the F-L curve at high ACT whereas other muscles (digital flexors) do so at low ACT. The interaction between tendon compliance, ACT and muscle lengths sheds new light on muscle recruitment and function during movement tasks. This interaction is particularly important in animals with high tendon compliance (e.g. cursorial species).
