Intra-rater reliability of hip abductor isometric strength testing in a standing position in older fallers and non-fallers

Background: Reduced hip muscle strength has been shown to be a major factor related to falls in older persons. However, comprehensive assessment of hip abduction strength in the clinical setting is challenging. The aim of this study was to investigate the feasibility and intra-rater reliability of a quick and simple hip abductor strength test in a functional standing position. Methods: Individuals over 65 years of age were recruited from the geriatric department of a university hospital and an outpatient clinic. Thirty-two older subjects, including 16 fallers (>= 1 fall during the last 12 months) and 16 non-fallers were included. Maximum voluntary isometric strength (MVIS) and rate of force generation (RFG) of the hip abductors of the right leg were evaluated in a standing position using a hand-held dynamometer. Two test-sessions were carried out. All hip strength values were normalized to participants' weight. Reliability was determined using the intra-class correlation coefficient agreement (ICCagreement), the standard error of measurement (SEM) and a Bland and Altman analysis (BA). Results: All participants completed the strength tests, which took a mean 2.47 +/- 0.49 min (one limb). Intrarater reliability was higher for MVIS (0.98([0.95-0.9)(4]))( )than RFG (ICC = 0.93([0.87-0.97])) for the entire sample. In the non-fallers, ICC was 0.98([0.95-1.00]) (SEM = 0.08 N.kg(-1)) for MVIS and 0.88([0.75-0.96]) for RFG (SEM = 1.34 N.kg(-1).s(-1)). In the fallers, ICC was 0.94([0.89-0.98] )(SEM = 0.11 N.kg(-1)) for MVIS and 0.93([0.84-0.98] )(SEM = 1.12 N.kg(-1).s(-1)) for RFG. The BA plot showed that the MVIS and RFG values did not differ across test-sessions, showing that no learning effect occurred (no systematic effect). The mean differences between test-sessions were larger and the LOA smaller in the fallers than in the non-fallers. Conclusion: Assessment of hip strength in a standing position is feasible, rapid and reliable. We therefore recommend this position for clinical practice. Future studies should investigate the diagnostic value of hip abductor strength in standing to discriminate between fallers and non-fallers, and to determine if change in strength following a falls prevention program reduces the risk of falls