Meeting Abstract
Tendons and other connective tissues in muscles are thought to play a dynamic role in many types of locomotion. By storing then releasing elastic energy, connective tissues can reduce metabolic costs and amplify power output. Such benefits are increasingly well documented in vertebrates for terrestrial, but not aerial, locomotion. One explanation for this discrepancy is that elastic mechanisms are less prevalent during aerial locomotion, because air does not provide a ground reaction force that can be absorbed and stored by muscle-tendon units. In birds, however, many flight muscles have long tendons, and some of these are hypothesized to facilitate powered flight by stretching then recoiling in opposition to each other, to decelerate then accelerate the wing during downstroke-upstroke or upstroke-downstroke transitions. To test whether these muscle-tendon units can recover useful elastic energy, we constructed a three-dimensional musculoskeletal model of the Collared-Dove (Streptopelia) and used simulations (OpenSim) to explore muscle-tendon dynamics during flight. Coupled with previous work on Chukar Partridges (Alectoris chukar) and in vivo kinematics and aerodynamic force measurements, our simulations suggest that the two main flight muscles of birds, the pectoralis (downstroke) and supracoracoideus (upstroke), have spring-like qualities. Both muscles produce force that decelerates then accelerates the wing, transitioning from negative to positive power in opposition to one another. These findings corroborate previous hypotheses and suggest that passive connective tissues in the pectoralis and supracoracoideus act as antagonistic springs that help birds meet the high power requirements associated with flapping flight.
