Myofibrillar ATPase activity in skinned human skeletal muscle fibres: Fibre type and temperature dependence

1. Myofibrillar ATP consumption and isometric tension (P₀) were determined in chemically skinned skeletal muscle fibres from human rectus abdominis and vastus lateralis muscle. Fibres were classified in four groups (I, II A, IIB, IIA/B or mixed) based on myosin heavy chain composition. 2. ATP consumption (± S.E.M.) at 20°C varied from 0·41 ± 0·06 mmol l^-1 s^-1 in type IIB fibres (n = 5) to 0·10 ± 0·01 mmol l^-1 s^-1 in type I fibres (n = 13). 3. The ratio between ATPase activity and P₀ (tension cost) differed significantly between fast type II and slow type I fibres. At 12°C tension cost was lower than the values found previously in corresponding fibre types in the rat. 4. The relative increase in ATPase activity for a 10°C temperature change (Q₁₀), determined in the range from 12 to 30°C, was temperature independent and amounted to 2·60 ± 0·06. The increase in P₀ with temperature was smaller and declined when the temperature increased. 5. From these measurements, estimates were obtained for the maximum rate of isometric ATP consumption and force development at muscle temperature in vivo (35°C).