Meeting Abstract
Maximum sprint speed should be determined by the contractile properties of muscles, but the exact nature of this link is unclear. It has been suggested that the rate at which a muscle can turn on and off, as measured by the time of a single muscle twitch, may set a limit to top speed by setting a minimum duration of stance or swing phase in a stride cycle. In Sceloporus lizards, the duration of a twitch in isolated limb muscles is approximately equal to the duration of stance phase during running at low but not high body temperatures, suggesting that the rate the muscles can turn on and off may limit sprint performance at certain temperatures. We studied muscle properties and sprint kinematics in two species of Anolis lizards, A. cristatellus and A. sagrei, to determine if muscle twitch times were closely matched to stance and swing times during running. Both species were maintained at field body temperatures (29.1°C and 32.0°C) and run over a trackway at five different inclines. Twitches were elicited in isolated limb muscles, and twitch time was measured as the onset of force to the time of 50% relaxation. Stance and swing times were variable at all speeds, but consistently reached minimum values that corresponded to the twitch time measured in isolated muscles. Furthermore, differences in muscle twitch time between the two species correlated with differences in kinematics. The average muscle twitch time for A.sagrei was approximately 71% that of A. cristatellus, similar to the difference (78%) in minimum stance time. These data suggest that A.sagrei are able to cycle their limbs faster than A. cristatellus due to their lower muscle twitch time. It is well established that morphological variation correlates to variation in sprint speed among Anolis lizards. These results suggest that muscle properties are also important determinants of locomotor performance. This research was supported by NSF grant IOS 1354620.
