A comparison of the effects of electrode placement, muscle tension, and isometric torque of the knee extensors.

Numerous electrical stimulation (ES) papers have been published using a variety of electrode placements and muscle tension criteria levels, making cross-comparisons difficult. The purpose of this study was to compare isometric knee extensor torques produced using three methods to induce muscle tension and three electrode placements. Twenty-three healthy, informed female volunteers (mean age = 24 yrs, SD = 3.2 yrs) participated in a practice session and three test sessions, each approximately 48 hrs apart. One of three electrode placements was randomly assigned during each test session. Maximal voluntary isometric contractions (MVIC) preceded the electrically induced isometric torque outputs. Comfortably tolerable and maximally tolerable ES intensities were combined with each of the following electrode placements: 1) lumbosacral plexus/femoral triangle (LS), 2) femoral triangle/transverse distal quadriceps (F), and 3) transverse proximal/distal quadriceps muscle (Q). A two-way ANOVA with repeated measures, Neuman-Keuls, and tests of simple main effects were used to analyze the data. Significantly greater torques were produced during the MVlCs than during either type of electrically induced isometric torque output (p < 0.05). During ES, the maximally tolerable intensity level produced significantly greater torques than the comfortably tolerable intensity level (p < 0.05). The F and Q electrode placements produced similar torques, both significantly greater than the torque produced with the LS electrode placement (p < 0.05). The method to induce muscle tension (voluntary or electrically induced), the criteria defining the level of muscle tension (MVIC, maximally or comfortably tolerable ES), and the electrode placement (LS, F, or Q) affect knee extensor torques and should be considered when using ES and when interpreting ES studies. Although the ideal rehabilitation program typically includes voluntary exercise to provide overload, certain pathologies may contradict this choice. In its place, ES has the potential to minimize strength losses or create gains while offering joint protection. J Orthop Sports Phys Ther 1992;15(4):168-174.