Abstract
The objective was to better understand how a series compliance alters contraction kinetics and power output of muscle to enhance the work done on a load. A mathematical model was created in which a gravitational point load was connected via a linear spring to a muscle (based on the contractile properties of the sartorius of leopard frogs, Rana pipiens). The model explored the effects of load mass, tendon compliance, and delay between onset of contraction and release of the load (catch) on lift height and power output as measures of performance. Series compliance resulted in increased lift height over a relatively narrow range of compliances, and the effect was quite modest without an imposed catch mechanism unless the load was unrealistically small. Peak power of the muscle-tendon complex could be augmented up to four times that produced with a muscle alone, however, lift height was not predicted by peak power. Rather, lift height was improved as a result of the compliance synchronizing the time courses of muscle force and shortening velocity, in particular by stabilizing shortening velocity such that muscle power was sustained rather than rising and immediately falling. With a catch mechanism, enhanced performance resulted largely from energy storage in the compliance during the period of catch, rather than increased time for muscle activation before movement commenced. However, series compliance introduced a trade-off between work done before versus after release of the catch. Thus, the ability of tendons to enhance locomotor performance (i.e. increase the work done by muscle) appears dependent not only on their established role in storing energy and increasing power, but also on their ability to modulate the kinetics of muscle contraction such that power is sustained over more of the contraction, and maximizing the balance of work done before versus after release of a catch.
Highlights
ObjectivesOur objectives were to assess: 1) how tendon compliance impacts work and power from muscle and tendons and how this relates to locomotor performance, and 2) how tendon compliance interacts with load mass and mechanical catch delay to influence muscle contraction kinetics in a manner that results in increased work done and imparted to the load
Animals that employ single, ballistic body movements rely on contraction of skeletal muscle to load their tendons, aponeuroses, and other series compliances that subsequently move the body
Our objectives were to assess: 1) how tendon compliance impacts work and power from muscle and tendons and how this relates to locomotor performance, and 2) how tendon compliance interacts with load mass and mechanical catch delay to influence muscle contraction kinetics in a manner that results in increased work done and imparted to the load
Summary
Our objectives were to assess: 1) how tendon compliance impacts work and power from muscle and tendons and how this relates to locomotor performance, and 2) how tendon compliance interacts with load mass and mechanical catch delay to influence muscle contraction kinetics in a manner that results in increased work done and imparted to the load. The objective of the present study was to describe the effects of tendon compliance on muscle performance, measured as the ability to lift a load, and not a particular muscle or system of jumping
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