An electromyographic comparison of 4 closed chain exercises.

OBJECTIVE: Closed chain exercises are used in the clinical setting to safely strengthen the muscles about the knee. We compared the EMG activity of 3 muscles (vastus lateralis, vastus medialis, and biceps femoris) during 4 closed chain exercises (unilateral one-quarter squat, lateral step-up, FlexCord front pull, and FlexCord back pull) to determine which exercise produced the most muscle activity. DESIGN AND SETTING: We used a 4 x 3 x 2 factorial design with repeated measures on exercise, muscle, and movement (knee flexion and extension). Muscle and movement were the control variables for post hoc comparisons. Data were collected in a sports injury research laboratory. SUBJECTS: Thirty-eight healthy, active female college students aged 21.97 +/- 2.8 years, with height 166.9 +/- 6.3 cm and weight 61.9 +/- 8.5 kg. Subjects had no history of lower extremity pathology that resulted in surgery and no lower extremity pathology within the last year. MEASUREMENTS: We placed surface electrodes on the vastus lateralis, vastus medialis, and biceps femoris muscles. Synchronized with a metronome, subjects performed 3 repetitions of 4 exercises between 5 degrees and 30 degrees of knee flexion. Electromyographic measurements were taken from the middle third of the flexion and extension phase of each repetition. RESULTS: The FlexCord front pull and back pull produced higher levels of biceps femoris activity than the quarter squat and step-up. The FlexCord front pull also produced a higher level of vastus medialis activity during knee extension than the quarter squat, lateral step-up, or FlexCord back pull. CONCLUSIONS: The high levels of biceps femoris activity during the FlexCord exercises indicate that a greater cocontraction exists. With a greater cocontraction, the FlexCord exercises could be safely used during ACL rehabilitation. The high levels of vastus medialis activity during the FlexCord front pull suggest that it may be a beneficial exercise for patellofemoral rehabilitation.