ALTERATION OF A MUSCLE'S NORMAL RANGE OF MOTION AND POSITIONING RESULTS IN CHANGES IN FUNCTION AND ACTIVATION
Stoutenberg, M., Pluchino, A., Lewis, J. E., Gao, J.,& Signorile, J. F. (2009). Optimal range of motion for maximal EMG activation of the superficial quadriceps muscles. ACSM 56th Annual Meeting, Seattle, Washington. Presentation number 724.
"Patellofemoral Pain Syndrome is the clinical presentation of anterior knee pain related to physical and biomechanical changes in the patellofemoral joint. One of the more common methods for alleviating PFPS is restoring patellar alignment through quadriceps strengthening exercises, such as leg extensions. Additionally, range of motion and limb position can be manipulated to maximize superficial quadriceps muscles activity, while avoiding undue negative knee joint stresses."
This study examined variations in electromyographical (EMG) activity of the superficial quadriceps muscles during eight repetitions of leg extensions through three ranges of motion using three positions. Men and women (N = 24) performed eight leg extension repetitions at 70% of their 8-RM with their lower limbs medially rotated, laterally rotated, and neutrally positioned. For each repetition, EMG was averaged over the first, middle, and final 30 degrees of range of motion.
For the Vastus Medialis Oblique, significant effects were observed for range of motion, repetitions, and the interaction of range of motion and repetitions with increasing range of motion and repetitions generating higher levels of EMG activity. For the Rectus Femoris, significant effects were observed for positions and repetitions. Mean EMG activity increased across repetitions with lateral rotation generating the most activity of the three limb positions. For the Vastus Lateralis, significant effects were observed for position, range of motion, repetitions, and positions by range of motion interaction and repetitions by range of motion interaction. Increasing leg-extension range of motion and repetitions generated the highest EMG activity. Analysis of the range of motion by position interaction revealed that neutral and lateral rotation increased linearly across angles, while medial rotational activity was greatest in the middle 30 degrees.
Implication. For the Vastus Medialis Oblique, the greatest activity is generated in the final 30 degrees of range of motion regardless of position. Maximum EMG activity for the Rectus Femoris muscle can be achieved using lateral rotation within any range of motion. The Vastus Lateralis can be maximally activated by performing leg extensions using medial rotation over the middle 30 degrees of movement range or in neutral or lateral rotation over the final 30 degrees of the range of movement.
Altering positions and ranges of motion of major leg-extension muscles alters the responsiveness of each major muscle. This study shows that muscles have to be positioned correctly to function optimally. Changing a range of motion through a concerted stretching program could disadvantage a muscle’s force production, not improve it.
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