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.