Meeting Abstract
20.4 Monday, Jan. 4 Avian all-terrain: Tendons as power attenuators during rapid energy absorption KONOW, N.*; AZIZI, M.; ROBERTS, T.J.; Brown University; Brown University; Brown University nkonow@brown.edu
Muscles perform two very different tasks during jumping: they produce mechanical power for takeoff, and absorb it during landing. Tendons can be important in amplifying muscle power during takeoff, but their function in power absorption remains unclear. We studied Eastern wild turkeys landing from different heights to quantify the power-absorbing function of the lateral gastrocnemius muscle-tendon unit. We measured joint angle, muscle fascicle lengths and electrical activity, and used strain gauges on the calcified tendon to calculate muscle-tendon unit force. Landings elicited high muscle forces, approaching fourfold of those measured at intermediate running speed. Flexion of the ankle joint and muscle lengthening were consistently out of phase with joint flexion occurring in the first half of the contact period and muscle lengthening occurring in the second half. During most of ankle flexion, muscle fascicles shortened and did not absorb energy. Fascicle lengthening (30-40% fascicle strain) late in the contact period acted as a significant energy sink, absorbing over 20J/kg muscle. This length-change pattern is consistent with the idea that tendons play an important role in storing energy during the initial period of force development and subsequently releasing energy to do work on the muscle contractile elements during force decay. Estimates of instantaneous tendon power corroborate this interpretation. Peak instantaneous power input to the tendon is significantly greater than the peak instantaneous power input to muscle fibers. Energy-absorbing contractions often lead to muscle damage. Our results suggest that tendons can reduce the risk of muscle damage by acting as power attenuators during activities requiring rapid dissipation of mechanical energy. Supported by NIH grant AR055295.
