Reliability and Validity of Seated Hip Extensor Strength Measurement by Handheld Dynamometer in Older Adults

Background and Purpose: Muscle strength measurements with the handheld dynamometer are sometimes performed according to manual muscle testing. However, measuring hip extensor muscle strength in the prone position is difficult, since the some older adults have kyphosis or flexion contracture of the lower limbs. Alternatively, there is the standing position method of manual muscle testing, which accomodates those malalignments; however, it is known that the muscle strength of the lower limb that is not measured affects the measurement result. Hence, we devised the hip extensor strength measurement in a sitting position for healthy males in previous studies. This study examined the reliability and validity of the sitting measurement by a handheld dynamometer in older adults. Methods: Participants were 40 older adults (age [SD] = 82.4 [4.3] years). Measurements of isometric hip extensor muscle strength using a handheld dynamometer in 3 positions (sitting, standing, and prone) were conducted twice. A surface electromyogram was used to measure the activity of the gluteus maximus and the semitendinosus muscles. The reliability of muscle strength in each posture was examined with Cronbach a coefficient, intraclass correlation coefficients (ICCs1,1), and Bland-Altman analysis. The concurrent validity of muscle strength for the sitting and standing positions with reference to the prone position was examined with Spearman rank correlation and Bland-Altman analysis. Furthermore, muscle strength and muscle activity were compared between each posture. Results: The Cronbach alpha coefficient was 0.75. For each posture, the ICC1,1 was 0.86 to 0.87, with no systematic error in the sitting and prone positions. The sitting and standing positions were significantly associated with the prone position (r(s) = 0.72 and 0.42), with no systematic error between the sitting and prone positions. Proportional error was demonstrated between the standing and prone positions (P < .01). There was no significant difference in muscle strength between any posture. Gluteus maximus muscle activity was significantly higher in the sitting versus standing position (P < .05). Conclusion: The measurement of hip extensor muscle strength in the sitting position is a reliable and valid method in older adults, which can be effective even when the prone position is not possible.