Isokinetic contraction were performed with the knee extensor muscles in 15 young male soccer players. The measurements were obtained by a modified isokinetic device (Orthotron). In the range of motion the angular velocity was constant from 90 degrees to 20 degrees of knee flexion. The angular velocity could be varied from 30 to 360 degrees/s. The overall variation of the pre-set speed and the peak torque, as estimated from duplicate trials through the whole velocity range, averaged 4% and 5%, respectively. The peak torque decreased linearly with increasing angular velocity in a semilogarithmic scale. An estimate of the peak torque-velocity relationship in an experimental subject was obtained from the slope and the fibre composition in the lateral portion of the quandriceps muscle in this group of subjects especially trained in fast movements. It was concluded that the present applied isokinetic device gives the opportunities to measure force-velocity characteristics in the intact quadriceps muscle of man.