Quadriceps muscle training in a restricted range of motion: implications for anterior cruciate ligament deficiency

This study examined the transferability of strength gains associated with training in a limited range of motion, and at a specific joint angular velocity, to a different part of the range of motion. Work was assessed in control (N = 14) and experimental (N = 14) groups that performed baseline tests on a Kin-Com dynamometer at 1.05, 2.09, and 3.14 rad/sec, over a range of motion from 90 degrees flexion to full extension. The experimental group then underwent training consisting of three sets of eight maximum-effort knee extensions on a Kin-Com dynamometer at a joint angular velocity of 2.09 rad/sec, three times per week for 8 weeks. The range of motion at which they trained was 90 degrees to 45 degrees. After training, baseline tests were repeated in both groups. The findings showed that the work done by the quadriceps muscles of the experimental group increased significantly (p < .05) in the training range of motion across all joint angular velocities. In the untrained range of motion, the work done by the experimental group increased significantly (p < .05) only at the training angular velocity of 2.09 rad/sec. These findings provide evidence that training in a range of motion in which anterior shear forces are low can lead to changes in strength in the range of motion in which anterior shear forces are high. Hence, such exercise is of potential benefit to the anterior cruciate ligament-deficient individual.