Validity and Agreement of a Portable Dynamometer in Evaluating Hip Strength and Rate of Torque Development: Influence of Fixation Methods.

Abstract

Background: Portable dynamometers (PD) are widely used to assess hip muscle strength; however, few studies have explored their validity and agreement when evaluating the rate of torque development (RTD) of hip muscles, particularly with different fixation methods.

Hypothesis/purpose: The purpose of this study was to determine the validity and agreement of isometric hip strength and RTD using the PD with two fixation methods: placing the PD on the body (PDpush) or a treatment table (PDpull), compared to an isokinetic dynamometer (IKD). It was hypothesized that an PD would be a valid tool for assessing hip strength and RTD, with PDpull demonstrating strong validity and PDpush showing moderate validity; and its assessments would yield higher values than those obtained from IKD.

Study design: Cross-sectional study.

Methods: Twenty healthy, physically active individuals (10 females and 10 males) were included in this study. Hip abduction and extension strength (peak torque) and RTD (early phase: RTD0-100 ms and late phase: RTD100-200 ms) were assessed using PDpush, PDpull, and an IKD.

Results: Moderate-to-strong correlations were found between PD (both PDpush and PDpull) and IKD for all hip strength (r=0.46-0.73; p<0.05) and RTD (r=0.45-0.73, ρ=0.80; p<0.05) measures. PDpull demonstrated strong correlations for hip abduction RTD0-100 ms and hip extension strength and RTD100-200 ms (r=0.70-0.73; p<0.001), whereas PDpush showed moderate correlations (r=0.45-0.58; p<0.05). Bland-Altman plots with mean differences ± 95% limits of agreement indicated that the PDpush method overestimated all hip abduction and extension strength and RTD as compared to IKD. The PDpull method overestimated hip abduction and extension strength but had mixed results for RTD, either underestimating hip abduction RTD while overestimating hip extension RTD.

Conclusion: The PD is valid tool for evaluating hip strength and RTD, with PDpull offering strong validity for certain measures; however, PD measurements did not agree with the absolute values obtained from IKD.

Level of evidence: Level 3.