Passive compliance and length of clinically short hamstring muscles of healthy men.

This study examined the passive compliance and length of short hamstring muscles in relation to hamstring muscles not considered short in healthy men (ages 18-37). The right hamstrings of 30 men with straight-leg raising of 73.8° (group I) and 24 men with straight-leg raising of 61.0° (group 11) were compared. Subjects were positioned on their left sides with the pelvis stabilized and the right thigh fixed at 90°. Subjects received three maximal passive knee extension trials for data collection. Muscle activity was monitored with surface electromyography and passive resistance was measured with a dynamometer as the limb was photographed at force-dependent positions. Passive compliance was computed as the ratio of change in the knee angle to change in passive torque. Hamstring lengths were measured simultaneously. Results showed that the passive compliance curves for group II were shifted left compared to group I. Anovas revealed that the initial knee angles for group 11 were greater than for group I (P = 0.001), as were the maximal knee angles (P < 0.001). Passive compliance ratios for group 11 (1.29) were less than for group I (1.45), but not significantly different. Maximal passive torques were not different between groups. The change from initial muscle lengths to maximal lengths was less for group 11 than group I for the: (1) absolute length change (P = 0.027), (2) per cent change beyond initial length (P = 0.005), and (3) length change standardized as a percentage of femur length (P = 0.011).