Just as correct alignment and effective stabilization are basic elements of manual muscle testing and dynamometry, they are also crucial in resistance exercise. To strengthen a specific muscle or muscle group effectively and avoid substitute motions, appropriate positioning of the body and alignment of a limb or body segment are essential. Substitute motions are compensatory movement patterns caused by muscle action of a stronger adjacent agonist or a muscle group that normally serves as a stabilizer (fixator). If the principles of alignment and stabilization for manual muscle testing are applied whenever possible during resistance exercise, substitute motions can usually be avoided.

Alignment and muscle action. Proper alignment is determined by the direction of muscle fibers and the line of pull of the muscle to be strengthened. The patient or a body segment must be positioned so the direction of movement of a limb or segment of the body replicates the action of the muscle or muscle groups to be strengthened. For example, to strengthen the gluteus medius, the hip must remain slightly extended, not flexed; and the pelvis must be rotated slightly forward as the patient abducts the lower extremity against the applied resistance. If the hip is flexed as the leg abducts, the adjacent tensor fasciae latae becomes the prime mover and is strengthened.

Alignment and gravity. The alignment or position of the patient or the limb with respect to gravity may also be important during some forms of resistance exercises, particularly if body weight or free weights (dumbbells, barbells, cuff weights) are the source of resistance. The patient or limb should be positioned so the muscle being strengthened acts against the resistance of gravity and the weight. This, of course, is contingent on the comfort and mobility of the patient.

Staying with the example of strengthening the gluteus medius, if a cuff weight is placed around the lower leg, the patient must assume the side-lying position so abduction occurs through the full ROM against gravity and the additional resistance of the cuff weight. If the patient rolls toward the supine position, the resistance force is applied primarily to the hip flexors, not the abductors.

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