IRSCHICK, DUNCAN J.*; BOCCHI, STEVE; FULL, ROBERT J.: Does Power Limit Climbing Performance? Loading Small Climbing Lizards

Previous studies showed that power output does not limit the maximum running speed of lizards on the level. Geckos have an extraordinary ability to climb at high speeds. The ability of animals to produce power may not limit their maximum running speed on a horizontal surface, but may be the factor limiting climbing speed. We tested this hypothesis by examining the effects of adding loads (30-60% of body weight) to geckos (Hemidactylus garnoti, 2-4 g) running up a smooth vertical surface. We measured both the kinematics and kinetics of uphill locomotion by filming animals running over a force platform embedded in the wall. Speed declined only slightly (47 cm/s to 38 cm/s) when comparing unloaded running to running with a 60% load, suggesting that power output does not limit speed during climbing. Stride frequency remained almost constant with an increase in load (unloaded=16.7 Hz, 60% load=15.5 Hz, 7% change), but stride length decreased significantly (unloaded=2.8 cm, 60% load=2.4 cm, 17% change). Whole-body peak lateral forces decreased significantly (33%) as the amount of the load increased, and single-leg peak forces showed similar trends. Mean power output increased by 10% between the unloaded (5.19 W/kg) and the 60% load (5.69 W/kg). These data suggest that power output does not limit speed during uphill climbing, and also underscore the remarkable gripping abilities of gecko toepads.