Temperature is a potent modulator of skeletal muscle contractile and metabolic properties. An increase in muscle temperature, as a result of the ambient conditions or as a consequence of metabolic heat production, may influence energy turnover during exercise. The aim of this study was to investigate the effect of muscle temperature on human skeletal muscle energy turnover during single leg knee-extensor exercise.Nine male subjects performed dynamic knee extensor exercise for 10 min at a moderate intensity (~ 85% peak workrate, 43 ± 4 W; mean ± S.E.M.) and frequency of 60 contractions per minute. Exercise was performed under conditions of normal (N) and elevated muscle temperature (ET) through passive heating. Aerobic energy turnover (muscle oxygen uptake; VO₂) was determined from measurements of thigh blood flow (constant infusion thermodilution technique) and femoral arterial-venous differences for oxygen content (a-v O₂diff ). Anaerobic energy turnover was estimated from measurements of lactate release as well as muscle lactate accumulation and PCr utilisation based on analysis of muscle biopsies obtained before and after each exercise bout.Quadriceps muscle temperature at the start of exercise was 34.5 ± 0.6°C in N compared to 37.2 ± 0.2°C during ET (P < 0.05). Thigh VO₂ was the same between the two temperature conditions throughout exercise. However, analysis of the mono-exponential rise in VO₂ during the initial 3 min of exercise revealed a greater amplitude (P < 0.05) in ET compared to N (0.64 ± 0.07 vs. 0.48 ± 0.04 l min^-1 respectively). The total release of lactate was the same between conditions. There were no differences in lactate accumulation or PCr utilisation between temperature conditions. The mean rate of energy turnover (aerobic + anaerobic) was the same between each temperature condition (198.9 ± 9.4 vs. 209.0 ± 13.3 J s^-1 ;N and ET, respectively). These results demonstrate that passively elevating muscle temperature prior to moderate intensity single-leg knee-extensor exercise had no effect on skeletal muscle energy turnover. However, it was observed that the kinetics of the oxygen uptake response in the initial phase of exercise was influenced by muscle temperature.