The Influence of Sagittal Plane Hip Position on Lower-Extremity Muscle Activity and Torque Output

Hip muscle strength has previously been evaluated in various sagittal plane testing positions. Altering the testing position appears to have an influence on hip muscle torque during hip extension, abduction, and external rotation. However, it is unknown how altering the testing position influences hip muscle activity during these commonly performed assessments.

To evaluate how hip sagittal plane position influences hip muscle activation and torque output.

Cross-sectional.

Laboratory.

A total of 22 healthy females (age = 22.1 [1.4] y; mass = 63.4 [11.3] kg; height = 168.4 [6.2] cm) were recruited.

None.

Participants completed isometric contractions with surface electromyography on the superior and inferior gluteus maximus; anterior, middle, and posterior gluteus medius; biceps femoris, semitendinosus, adductor longus, and tensor fascia latae. Extension and external rotation were tested in 0°, 45°, and 90° of hip flexion and abduction was tested in -5°, 0°, and 45° of hip flexion. Repeated-measures analysis of variances were used for statistical analysis (P ≤ .01).

Activation of gluteal (P < .007), semitendinosus (P = .002), and adductor longus (P = .001) muscles were lesser for extension at 90° versus less flexed positions. Adductor longus activity was greatest during 90° of hip flexion for external rotation torque testing (P < .001). Tensor fascia latae (P < .001) and gluteus maximus (P < .001) activities were greater in 45° of hip flexion. Significant differences in extension (P < .001) and abduction (P < .001) torque were found among positions.

Position when assessing hip extension and abduction torque has an influence on both muscle activity and torque output but only muscle activity for hip external rotation torque. Clinicians should be aware of the influence of position on hip extension, abduction, and external rotation muscle testing and select a position most in line with their clinical goals.