Eledromyographic Analysis of Knee Rehabilitation Exercises

T he knee is a frequently injured area that often requires assessment by a physician and a physical therapist. Some injuries need only rest o r reassurance, while others require some form of therapy to return the patient to his o r her preinjury state. Others may need surgical intervention and postoperative rehabilitation (2 1). Knee rehabilitative exercises continue to be defined and redefined by clinical experience, observations, and basic science research. T h e general goals of knee rehabilitation are to increase strength, endurance, and range of motion. T o reach these goals, the exercises must be performed through a safe range of motion and be efficient and effective (24). Electromyography (EMG) is an appropriate tool to measure the relative intensity of muscle activity occurring during exercises o r functional activities (1 6). Soderberg and Cook and Soderberg e t al, in two separate studies during the 1980s. analyzed the surface EMG activity of four lower extremity muscles during quadricep femoris muscle setting (quad sets) and straight leg raises (SLR) (23,24). In both reports, more muscle activity was found in the vastus medialis, biceps femoris, and gluteus medius during quad sets than during SLR. T h e rectus femoris was Many exercises are used to strengthen the knee muscles, yet limited studies that evaluate the exercises exist. The purpose of this study was to describe and compare the muscle firing patterns in five knee muscles during five rehabilitative exercises, which were presumed either to strengthen a specific muscle group or to elicit a cocontraction. During short-arc knee extension, the medial and lateral vasti were significantly more active during the last 15 of extension than during other arcs (p < .05). The short-arc knee extension with hamstring cocontraction demonstrated significantly more activity in the rectus fernoris, vastus rnedialis oblique, and vastus lateralis than the biceps femoris and semimembranosus in the final 15 of extension (p < .05). With isometric knee cocontractions, no significant difference in muscle activity occurred in any of the arcs tested. During squatting, the rectus femoris, vastus medialis oblique, and vastus lateralis were significantly more active than the biceps femoris and semimembranosus during the descending, holding, and arising phases (p < .05). This information offers suggestions in selecting optimal knee rehabilitation exercises.