Meeting Abstract
4.3 Saturday, Jan. 4 08:30 Mechanics of proximal limb muscle tendon units in a small flying mammal KONOW, N.*; ROBERTS, T.J.; BOERMA, D.; VON BUSSE, R.; SWARTZ, S.M.; Brown Univ. Providence; Brown Univ. Providence; Brown Univ. Providence; Brown Univ. Providence; Brown Univ. Providence nkonow@brown.edu
The role of tendon elasticity in muscle function is unclear for flying animals, and for small mammals. Bats are small and have wing muscles with relatively large, proximally located muscle bellies actuating the wing via long slender tendons. Given their length, these tendons might reduce wing inertia by keeping muscle mass close to the body. Their length and slenderness also suggest that wing tendons may stretch significantly to store and recover elastic energy during flight. We looked for evidence of tendon stretch during ascending flight in the phyllostomid fruit bat Carollia perspicillata. We measured triceps and biceps muscle length and activity, as well as elbow and shoulder joint position using biplanar high-speed fluoromicrometry, electromyography and XROMM. Triceps muscle fiber length was almost entirely decoupled from elbow movement. During downstroke, the elbow flexed while the triceps muscle actively shortened and the tendon was stretched. During upstroke, triceps tendon recoil provided energy that could help extend the elbow. XROMM modeling of shoulder and elbow kinematics clarified the function of the biarticular biceps. There was a tighter coupling between muscle fiber length and joint position than for triceps. Biceps tendon stretch occurred briefly, around the time of peak elbow extension, when the muscle operated eccentrically and the wing membrane was aerodynamically loaded. Eccentric muscle contraction produces high force, which may be needed to stretch the biceps tendon. In conclusion, the tendons of both triceps and biceps were stretched during ascending flight in C. perspicillata. Differences between the muscles in the decoupling of muscle fiber length and joint position may owe to differences in muscle activity timing relative to aerodynamic loading.
