Meeting Abstract

98.9  Wednesday, Jan. 7  The series elastic shock absorber: tendon elasticity reduces peak muscle forces during active lengthening ROBERTS, T.J.*; AZIZI, E.; Brown University thomas_roberts@brown.edu

Tendons store and release mechanical energy when force is applied to them. This spring-like behavior can conserve muscle mechanical power for cyclical activities like running, or amplify it for high-power activities like jumping or acceleration. The function of tendon springs during dissipative activities such as deceleration or jumping landing has received relatively little attention. We used an in situ muscle preparation (turkey gastrocnemius) to test the hypothesis that tendon stretch limits the peak forces developed in a lengthening contraction. Implanted sonomicrometer crystals measured muscle contractile element length and a muscle servomotor measured muscle force and muscle-tendon length. A series of constant velocity ramp stretches were applied to the muscle-tendon coincident with a 50ms stimulation pulse. Under most conditions, the contractile element shortened during force rise, even as the muscle-tendon unit lengthened. Muscle fascicle lengthening could be elicited only at the most rapid rates of muscle-tendon lengthening. Forces developed when muscle fascicles were stretched at a rate equivalent to 10% maximal shortening velocity were almost twice the magnitude of forces developed when the same stretch was applied to the muscle-tendon unit. During force decline, muscle contractile elements actively lengthened, but at a rate that was usually slower than the stretch applied by the muscle motor. These results describe a tendon-mediated buffering mechanism that may limit the risk of excessive forces and muscle damage during rapid energy-absorbing tasks. Supported by NIH grants AR 055295 to TJR and AR054246 to EA.