Position- and Sex-Related Differences in Sagittal and Frontal Plane Concentric Isokinetic Hip Muscle Peak Torques and Agonist-Antagonist Ratios.

Background: Hip muscle weakness is associated with many musculoskeletal conditions and athletic injuries. Isokinetic testing is often performed to measure a patient's strength or to assess treatment response. Patient sex and positioning during isokinetic strength testing may influence peak torque production and the agonist-antagonist peak torque ratios. However, different test positions are used clinically and in research to measure hip muscle strength. It is unknown how patient test position or sex impacts test results.

Hypothesis/purpose: The purpose of this study was to determine whether concentric isokinetic peak torques of sagittal and frontal plane hip muscles differ when tested in recumbent versus standing positions and if results were impacted by patient sex.

Study design: Cross-sectional observational.

Methods: Forty healthy adults (20 male, 20 female) participated. Concentric isokinetic hip torques of the hip flexors, extensors, abductors, and adductors were measured with participants in two positions (recumbent versus standing; 60°/second angular velocity). Peak torque values were normalized by body mass and height. Data were analyzed with mixed-model ANOVAs (sex x position). Effect sizes were examined using partial eta squared.

Results: No significant interactions or main effects for sex were found. Significant main effects for position were found for hip extensor and abductor peak torques and for hip flexor-extensor ratio. Hip extensor peak torque was greater when tested supine versus standing with a large effect size (p=.02, effect size =.14). Hip abductor peak torque was greater when tested sidelying versus standing with a medium effect size (p=.03, effect size =.12). Hip flexor-extensor agonist-antagonist ratio was greater when tested standing versus supine with a large effect size (p<.001, effect size =.27).

Conclusion: Hip extensor and abductor concentric isokinetic peak torques were greater when tested in recumbent versus standing positions. In contrast, hip flexor-extensor ratio was greater when tested in standing versus supine.

Level of evidence: 3.