Meeting Abstract

6.5  Wednesday, Jan. 4  Effect of Motor Unit Recruitment on In Vivo Muscle Function LEE, S/SM*; BIEWENER, A/A; DE BOEF MIARA, M; ARNOLD, A/S; WAKELING, J/M; Simon Fraser University; Harvard University; Harvard University; Harvard University; Simon Fraser University

A mixture of motor unit types can be found in mammalian skeletal muscles, and recruitment of these different motor units may influence whole muscle performance. Key properties that dictate the mechanical output of muscle include the maximum shortening velocity and the activation/deactivation rates that can be important during fast or explosive movements such as galloping and jumping. The purposes of the study were to 1) describe changes in motor unit recruitment patterns due to changes in locomotor dynamics (gait velocity, surface incline, and locomotor activity) and 2) examine if these changes in motor unit recruitment patterns provide mechanical advantages by characterizing the relationships between motor unit activity, fascicle strain rate, and force profiles. We collected electromyography (EMG), tendon force, and sonomicrometry data in the gastrocnemius muscles of 9 goats during jumping and during walking, trotting and galloping on a treadmill (level,incline). Motor unit recruitment patterns were quantified with a wavelet analysis of the EMG signals. Our analysis demonstrates that motor units in the goat hindlimb are preferentially recruited for different locomotor tasks and that recruitment is related to fascicle shortening rate and force rise and relaxation rates. Shortening velocities, and force rise and relaxation rates were significantly different between activities (jump vs. gait,p<0.001, and gallop vs. trot and walk,p<0.001), and grade (level and incline,p<0.001). Also, motor unit recruitment was associated with strain rate (p<0.001), force rise and relaxation rates (p< 0.01) and myoelectric intensity (p<0.001). This study offers new insight into the complex relationships between motor unit recruitment, strain rate, and force generation during different locomotor tasks. (NIH R01AR055648)