Thermal dependence of isotonic contractile properties of skeletal muscle and sprint performance of the lizardDipsosaurus dorsalis

Contractile properties of the fasttwitch glycolytic (FG) portion of the iliofibularis muslce and sprint running performance were studied at approximately 5°C intervals from 15–44°C in the lizardDipsosaurus dorsalis. Maximal running velocity (V_R) and stride frequency (f) were both greatest when body temperature (T _b) was 40°C, the field-active,T _b inDipsosaurus. At 40°C V_R was 4.3±0.2 m/s and f was 13.5±0.5 s⁻¹. Between 25 and 40°C, the thermal dependencies of V_R and f were approximately constant (Q₁₀'s of 1.31 and 1.36 for V_R and f, respectively). Below 25°C performance declined more markedly with decreasing temperature. At 20°C strides were qualitatively normal, but V_R was only half of the value at 25°C. At 15°C the lizards were substantially incapacitated, and V_R was 10% of the value at 20°C. Stride length was approximately 0.33m and changed very little withT _b from 20–44°C. The time dependent contractile properties of FG muscle were affected more by temperature than was sprint performance. The maximal velocity of shortening at zero load (V_o) was 18.7 l₀/s at 40°C and had a Q₁₀ of 1.7 from 25–40°C. Maximal power output ( \(\dot W_{max} \) ) determined from the forcevelocity curve was 464 W/kg at 40°C. Below 40°C \(\dot W_{max} \) varied with temperature with a Q₁₀ of 2–3. The shape of the force-velocity curve changed little with temperature ( \(\dot W_{max} \) /P_OV_O=0.11). Between 25 and 40°C a relatively temperature-independent process must modulate the effects of temperature on the contractile properties of the muscles that supply the power for burst locomotion. Storage and recovery of elastic energy appears to be a likely candidate for such a process. Below 25°C, however, the contraction time is prolonged to such an extent that the f attainable is limited by the minimum time taken to contract and relax the muscles.