Relative torque contribution of vastus medialis muscle at different knee angles

We investigated the relative contribution of the vastus medialis (VM) muscle to total isometric knee extension torque at 10 degrees , 30 degrees , 60 degrees and 90 degrees knee flexion. In the past a more prominent role of the VM muscle at more extended knee angles has been put forward. However, different components of the quadriceps muscle converge via a common distal tendon. We therefore hypothesized that the relative contribution of the VM to total knee extension torque would be similar across angles.

At each knee angle the EMG isometric torque relations [20%, 25%, 30%, 35% maximal voluntary contraction (MVC)] of the rectus femoris (RF), vastus lateralis (VL) and VM muscle were established in 10 healthy male subjects; rectified surface EMG was normalized to M-wave area. Subsequently, the VM was functionally eliminated by selective electrical surface stimulation with occluded blood flow.

There was no evidence for preferential activation of VM at any of the knee angles. Following VM elimination, total knee extension torque during maximal femoral nerve stimulation (three pulses at 300 Hz) at 10 degrees , 30 degrees , 60 degrees and 90 degrees , respectively, decreased (P < 0.05) to (mean +/- SD): 75.7 +/- 12.2, 75.1 +/- 9.3, 78.2 +/- 7.2 and 76.0 +/- 5.8% (P > 0.05 among knee angles). In addition, during voluntary contractions at 20% MVC the increases in torque output of RF and VL compensating for the loss of VM function were calculated from the increases in EMG and found to be similar (P > 0.05) at 10 degrees , 30 degrees , 60 degrees and 90 degrees values (%MVC), respectively, were: 9.1 +/- 6.8, 7.5 +/- 2.9, 5.9 +/- 3.7 and 6.9 +/- 3.4.

The present findings support our hypothesis that the VM contributes similarly to total knee extension torque at different knee angles.