Meeting Abstract
The avian pectoralis produces most of the power for flight and is well suited to studies of how muscle properties affect flight performance. Previous work has linked kinematics to in vitro estimates of power output and examined in vivo pectoralis force production and length change. This study is the first to relate in situ force-length properties of the pigeon pectoralis to its in vivo force-length flight patterns. Muscle activation (via electromyography) and length changes (via sonomicrometry) were recorded in vivo during level flight. Active and passive force-length curves were determined in situ by quantifying fascicle length with sonomicrometry and force with a load cell at the muscle’s insertion on the humerus. In vivo fascicle strains ranged from ~90 to 120% lo (length at peak active force, Po). Based on past studies, we estimate that maximum in vivo pectoralis force occurs at ~110% lo, on the descending limb of the muscle’s active force-length curve. The estimated total force (active+passive) at 110% lo is 97% Po. Passive force develops at 97% lo, increasing steeply up to 30% Po at the largest strains (120% lo). Our results indicate that the pectoralis produces force to power level flight on both the ascending and descending limbs of its force-length curve and passive force is substantial at the upstroke-downstroke transition. Although in vivo active force production is maximal on the descending limb of the muscle’s force-length curve, total force is similar to Po at these lengths. Thus, passive force compensates for reduced active force and could provide elastic energy storage in the muscle’s aponeurosis and central tendon to assist in wing deceleration at the end of upstroke and wing acceleration as the muscle develops active force early in downstroke.
