Meeting Abstract

P3.55  Jan. 6  Forelimb kinematics and hand postures in the rhesus monkey (Macaca mulatta) PATEL, B.A.; Stony Brook University bapatel@ic.sunysb.edu

A digitigrade limb posture, considered to be a hallmark of cursoriality in terrestrial animals, is perceived to: 1) increase effective limb length (ELL) to achieve preferred or higher locomotor speeds more efficiently by increasing step length and step duration; and 2) help attenuate torques around distal joints and stresses in distal limb elements by assuming a more extended limb posture. Among primates, digitigrade hand postures typical of other mammals are rare. This study explores why some monkeys adopt digitigrade hand postures by evaluating hand and forelimb kinematics during quadrupedal locomotion in rhesus monkeys (Macaca mulatta). Two adult females were filmed moving unrestrained along a horizontal runway instrumented with a force plate. Kinematics and forces were recorded during stance phase. Hand postures were measured as the angle between the metacarpal shaft and the ground (MGA). A total of 200 symmetrical gait steps (speed=0.4-2.9m/s) were analyzed; 130 steps included force data. As predicted, a larger MGA yielded a longer step length, step duration, and ELL (when controlling for speed). However, contrary to expectations, subjects used more palmigrade postures (smaller MGA) at higher speeds (with higher GRF). At slow to preferred (median) speeds, subjects used more digitigrade postures (larger MGA). More digitigrade postures at slower speeds may be more efficient by increasing step durations and mechanical advantage of antigravity muscles to lower torques around the wrist joint and possibly lower metacarpal stresses. At higher speeds, palmigrade postures may be better suited to 1) take advantage of elastic strain energy of tendons that cross distal joints and 2) to distribute GRFs across the entire palm of the hand. Thus, digitigrady in primates appears to differ from that of other animals. Funded by NSF.