The effect of temperature on skeletal muscle ATP turnover and muscle fiber conduction velocity (MFCV) was studied during maximal power output development in humans. Eight male subjects performed a six second maximal sprint on a mechanically-braked cycle ergometer under conditions of normal (N) and elevated muscle temperature (ET). Muscle temperature was passively elevated through the combination of hot water immersion and electric blankets. Anaerobic ATP turnover was calculated from analysis of muscle biopsies obtained before and immediately after exercise. MFCV was measured during exercise using surface electromyography. Pre-exercise muscle temperature was 34.2 ± 0.6 °C in N and 37.5 ± 0.6 °C in ET. During ET the rate of ATP turnover for PCr utilization (temperature co-efficient Q₁₀ = 3.8), glycolysis (Q₁₀ = 1.7) and total anaerobic ATP turnover (Q₁₀ = 2.7; 10.8 ± 1.9 vs 14.6 ± 2.3 mmol.kg^-1 (dm)s^-1) were greater than during N (P<0.05). MFCV was also greater in ET than in N (3.79 ± 0.47 to 5.55 ± 0.72 m.s^-1). Maximal power output (Q₁₀ = 2.2) and pedal rate (Q₁₀ = 1.6) were greater in ET compared to N (P<0.05). The Q₁₀ of maximal and mean power were correlated (P<0.05; R = 0.82 and 0.85, respectively) with the percentage of myosin heavy chain (MHC) type IIA. The greater power output obtained with passive heating was achieved through an elevated rate of anaerobic ATP turnover and MFCV, possibly due to a greater effect of temperature on power production of fibers with a predominance of MHC IIA at the contraction frequencies reached.