(collaboration with R.V. Baudinette, University of Adelaide)
In a series of studies we have examined how the design of hindleg muscles and tendons of tammar wallabies (T. eugenii) favors economical force generation and elastic energy savings during level hopping. Our previous work of level hopping shows that two key leg muscles, the plantaris and lateral gastrocnemius, undergo very little length change when developing force to support the animal's weight during stance. As a result, the muscles perform little work, but are designed well for generating a high level of force with reduced energy expenditure. This facilitates the role of these muscles' long tendons for elastic energy storage and recovery. Over a range of hopping speeds, the bouncing, spring-like gait of these animals enables their leg tendons to recover as much as 25% of the work that their muscles would otherwise have to perform, potentially reducing their metabolic cost of transport by as much as 50%.
We are now interested in what happens when these animals hop up an incline, which requires increased positive muscle work. Will these muscles contribute usefully to the required increase in muscle work by shortening more? Or, will they be limited by their architecture to operate isometrically, requiring that the additional muscle work be performed by hip and/or knee extensors for the additional work required?