Reliability and validity of belt-stabilized and tension dynamometry for assessing hip strength and power in uninjured adults

Objectives: To investigate the intra-rater reliability and validity of belt-stabilized and tension dynamometry to assess hip muscle strength and power. Design: Repeated measures. Setting: Biomechanics laboratory. Participants: Seventeen uninjured adults (age = 22.0 ± 2.3y; 13 females). Main outcomes measures: Peak torque (strength) and rate of torque development (RTD; power) were measured for hip abduction, internal rotation, external rotation and extension using an isokinetic dynamometer, and belt-stabilized and tension dynamometry. Results: For peak torque assessment, belt-stabilized and tension dynamometry showed good (Intraclass Correlation Coefficient [ICC] = 0.848–0.899) and good-to-excellent (ICC = 0.848–0.942) reliability, respectively. For RTD, belt-stabilized dynamometry showed fair reliability for abduction (ICC = 0.524) and good reliability for hip internal rotation, external rotation, and extension (ICC = 0.702–0.899). Tension dynamometry showed good reliability for all motions when measuring RTD (ICC = 0.737–0.897). Compared to isokinetic dynamometry, belt-stabilized and tension dynamometry showed good-to-excellent correlations for peak torque assessment (r = 0.503–0.870), and fair-to-good correlations for RTD (r = 0.438–0.674). Bland-Altman analysis showed that measures from belt-stabilized and tension dynamometry had clinically meaningful disagreement with isokinetic dynamometry. Conclusion: Tension dynamometry is reliable for assessing hip strength and power in all assessed motions. Belt-stabilized dynamometry is reliable for assessing internal rotation, external rotation, and extension. Validity of both methods is questionable, considering the lack of agreement with isokinetic dynamometry.