A performance comparison of neuromuscular electrical stimulation protocols for isolated quadriceps contraction versus co-contraction of quadriceps and hamstrings

A Neuromuscular Electrical Stimulation (NMES) protocol that incorporates co-contraction of the quadriceps and hamstrings may provide greater functional benefits for knee rehabilitation. It is unclear if the addition of a co-contraction will affect the desired torque outputs of one or two of the involved muscle groups. Due to the proposed functional benefits of co-contraction, it may be beneficial to test the addition of a co-contraction electrical muscle stimulation. In this study we recruited 14 participants with whom we compared two NMES protocols; isolated quadriceps contraction (k-NMES) versus co-contraction of quadriceps and hamstrings (co-NMES). We examined peak knee extension evoked torque, current intensities required to produce given torque outputs, and self-reported discomfort levels at given torques. At maximum tolerable intensity peak torque output was similar in k-NMES versus co-NMES. To achieve specific submaximal levels of torque output as percentages of maximum voluntary contraction (MVC), a higher current intensity was required for co-NMES yet with no greater level of discomfort. Results suggest that clinicians who wish to achieve a co-contraction of quadriceps and hamstrings as part of a rehabilitation programme can use co-NMES without having to sacrifice the strength of contraction achieved in the quadriceps. This could lead to better functional outcomes, though more work is required to confirm this.