The ATP content was measured in type I and type II fibres from human vastus lateralis muscle at rest, after electrical stimulation and during recovery. At rest the mean values were 25.2 +/- 4.02 and 25.9 +/- 3.62 mmol kg-1 dry muscle (mean +/- SD) for type I and type II fibres respectively. Normal distribution curves were found for both types I and II fibres. After intermittent electrical stimulation for 83 s (1.6 s stimulation, 1.6 s pause) with occluded blood flow, the force generation decreased to 22% of the initial value and the muscle tissue showed a mean decrease in ATP to 14.8 and in phosphocreatine to 5.44 mmol kg-1 dry muscle; lactate increased to 128.9 mmol kg-1 dry muscle. The ATP content in isolated fibres was equally decreased in both fibre types to 16 mmol kg-1 dry muscle. In 11% of the fibres the ATP content was lower than 10 mmol kg-1 dry muscle. After 15 min rest with intact blood circulation ATP was completely resynthesized in type I fibres and to 91% in type II fibres.