Peak Torque Occurrence in the Range of Motion During Isokinetic Extension and Flexion of the Knee

The purpose of this study was to 1) assess the knee angles of hamstring and quadriceps peak torques at slow (60 degrees.sec-1) and moderate (180 degrees.sec-1) isokinetic velocities in healthy adult males (N = 143) and females (N = 106), 2) determine if velocity has an effect on these peak torque angles, and 3) determine if subject's age, sex, and muscle strength have an effect on the results. The Cybex II dynamometer was used to record the measurements. At 60 degrees.sec-1, the mean peak torque for the hamstrings occurred at 33 degrees for men and 37 degrees for women (p < 0.001) (0 degree = full extension). At 180 degrees.sec-1, the corresponding angles were 40 and 44 degrees (p < 0.01). In both groups the increase was 7 degrees (p < 0.001). At 60 degrees.sec-1, the peak torque angle of the quadriceps was 54 degrees in both groups. At 180 degrees.sec-1, the angle occurred significantly later in men (11 degrees later) and in women (10 degrees later) (p < 0.001 for both). Subject's age (18 to 40 years) did not affect the results. In female hamstrings, the knee angle of peak torque had a highly significant (p < 0.001) negative correlation to muscle strength; that is, in female hamstrings, the peak torque angles occurred later in the range of motion when muscle strength decreased. This possibly explained the difference observed between men and women in the peak torque angles of hamstrings. In conclusion, people involved in isokinetic testing of muscular performance should be aware that the peak torque occurs later in the range of motion with increasing angular velocity, especially when testing weak muscle groups. In high angular velocities this may become a problem since the limb may pass the optimal joint position for muscular performance, and the recorded peak torque may not represent the subject's maximal torque capacity.