UC Irvine

The fastest biological movement are capable of generating high mechanical power efficiently and repeatably. Many of the fastest movements are achieved by using a common mechanistic framework know as latch-mediated spring actuation (LaMSA). While the fundamental mechanisms associated with LaMSA have been described over the last decade, such advances have not yet been able to pinpoint the mechanical or physiological features that explain biological variation in whole system performance. Furthermore, predicted scaling relationships suggest that there is a continuum between elastic recoil use and direct muscle actuation where elastic recoil is most prevalent at small masses and organisms transition to direct muscle actuation at large sizes. These predictions provide a framework that motivates experimental approaches aimed at understanding how animals at intermediate size range partition direct muscle and spring actuation to power fast movements. In this dissertation, I investigated factors that influenced energy storage and energy release in frogs who are believed to use both LaMSA and direct muscle actuation to power jumping. First, I examined interspecific variation in the plantaris longus muscle-tendon unit (MTU) of three species of frogs to investigate how tuned properties of the MTU affected their capacity to store energy. I found that high energy storage capacity was achieved when both muscle force capacity and relative spring stiffness increased. Second, I investigated how a dynamic mechanical advantage latch affected energy storage and energy release while varying environmental temperature. I found that the while spring actuation accounts for a significant portion of the energy of a jump, muscles continue to contribute energy during spring actuation. The ability to contribute this mechanical energy during the actuation phase required high muscle power and therefore explained the thermal sensitivity observed in these systems. Lastly, I examined the energy stored and returned during frog jumps. I discovered that the muscle stored energy in elastic structures prior to any substantial movement, and that it contributed work to the jump during limb extension. I found that 70% of the total muscle fascicle work was done during the loading phase and 30% was done during the unloading phase. Taken together, my dissertation work demonstrated that variation in elastic energy storage and release could be a consequence of evolutionary differences, latch mechanics, and real time control of energy flow.