S5.1-2 Sunday, Jan. 5 08:30 Validation of Hill-type muscle models in relation to neuromuscular recruitment and force-velocity properties: predicting muscle force patterns. BIEWENER, Andrew*; WAKELING, James; LEE, Sabrina; ARNOLD-RIFE, Allison; HOLT, Natalie; Harvard University email@example.com
Muscle models are frequently used in musculoskeletal simulations of muscle function. However, such models are rarely validated against direct measures of muscle performance. Comparison of novel 2-element and standard 1-element Hill-type models with in situ and in vivo measures of goat gastrocnemius force and strain shows that 2-element models that allow independent recruitment of slow and fast units result in improved prediction of temporal force patterns. Recruitment patterns based on wavelet and principal component analysis were generally associated with in vivo fascicle strain rates, EMG intensity and muscle-tendon force, with faster units linked to greater strain rates and more rapid forces. To investigate the effect of motor unit recruitment on force-velocity properties of whole muscles, differential stimulation of rat plantaris muscles in situ were carried out under isotonic conditions. Unexpectedly, recruitment of subpopulations of fast or slow motor units resulted in slower force rise times, lower shortening velocities and less steeply curved F-V relationships. These results suggest significant inertial, viscous and elastic effects on muscle F&V when a subfraction of the muscle is recruited. Future muscle models need to take such effects into account to improve predictions of time-varying muscle force and work output (NIH AR055648).