Determining meaningful changes in hip abductor muscle strength obtained by handheld dynamometry

This study quantified the minimal detectable change (MDC), defined as the smallest change that falls outside the expected range of error, for isometric hip abductor muscle strength in healthy persons obtained with a handheld dynamometer (HHD). Ninety volunteers (45 males and 45 females) between the ages of 22 and 70 years participated in the study. Bilateral measurements of isometric hip abductor muscle force were obtained with a digital HHD using a "make" test with the subject in supine. All measurements were obtained by one female examiner. The muscle force measurements were normalized to a volunteer's body weight (BW). Intratester reliability of hip abductor muscle force was estimated by using an intraclass correlation coefficient (ICC(3,1)) and calculated to be 0.96. The standard error of measurement (SEM) was 2 Newtons. The MDC was calculated by using an appropriate formula that included a 95% level of confidence. The MDC(95) was 5.4% BW for males and 5.3% BW for females. If a person's isometric hip abductor muscle force production changes less than the MDC(95) value between measurements, then the muscle force production is within measurement error, and it can be determined there has been no change in the strength of hip abductor muscles.