If you are familiar with Florence Kendall's method of Manual Muscle Testing (MMT), you are likely aware of the fact that she prefers to test muscle strength in a partially shortened position. When muscle length is in mid-range, it allows optimal cross-bridge linking, leading to a higher potential for force production. When muscles are over-extended or excessively shortened, the muscles lose that high frequency of cross-bridge linking. If you look at Kendall's MMT for the gluteus medius, you might see that she tries to emphasize the posterior fibers by having the patient on the side with the pelvis tilted forward and hip in extension, abduction, and lateral rotation. This is position completely shortens the muscle, thus potentially lower the validity of strength assessment. We have already discussed the use of evaluating hip abduction strength in a closed-chain position. Something else to consider is the fact that the gluteus medius is essential for pelvic stability throughout the entire stance phase of the gait cycle, not just mid-stance (where Kendall tests). Does it really matter if you have a level pelvis at midstance if you cannot keep your pelvis stable at heel strike? We have been presented another method for testing the gluteus medius in open-chain. Instead, place the lower extremity in hip abduction, lateral rotation, and flexion. The examiner then applies a flexion and adduction directed force. This position allows the muscle to not be completely shortened and tested in a functionally useful position. The position of flexion that is added can mimic heel strike in the gait cycle, making certain the muscle is strong enough to prevent pelvic drop as soon as stance begins.
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