Meeting Abstract
To amplify power a number of invertebrates rely on anatomical latches that decouple the storage and release of elastic strain energy. To date, no anatomical latch has been found in vertebrates. However, frogs amplify power by using a dynamic shift in mechanical advantage (MA) that allows for slow storage and rapid release of elastic energy. We examine whether a fibrocartilage protrusion (lump) in the plantaris longus tendon can augment the storage and release of elastic energy by acting as a latch. If this structure were to function as a latch we predict tendon movement would be greater above vs. below the ankle joint when the frog leg was in a crouched position and the lump engaged. During leg extension and disengagement of the lump, the tendon would show similar displacement above and below the ankle joint. We isolated legs of bullfrogs (Lithobates catesbeianus) and secured the intact leg to a platform attached to a servomotor. The sciatic nerve was stimulated via a nerve cuff to elicit a contraction in the plantaris muscle. Trials were recorded at 500 fps and markers placed on the ankle joint and tendon were digitally tracked and analyzed. Results partially supported our hypothesis: the tendon moved more above vs. below the ankle joint. No difference was found in tendon movement when comparing the leg in a crouched position vs. extended, suggesting the lump did not act as a latch. The lump increased the muscle moment arm as it slid across the joint during ankle extension. The structure may augment an increase in effective MA during leg extension, a mechanism thought to be responsible for facilitating elastic energy storage and release in jumping frogs. Our results were confirmed by a physical model inspired by the frog leg where its anatomical and mechanical features could be broadly varied to further test our hypotheses.
