Enhancing the examiner's resisting force improves the reliability of manual muscle strength measurements: comparison of a new device with hand-held dynamometry.

OBJECTIVE To develop and determine the reliability of a newly -designed resistance-enhanced dynamometer for muscle strength measurement, and to test the hypothesis that enhancing the examiner's resisting force improves the reliability of manual muscle strength measurements. DESIGN An intra-examiner, inter-examiner, intra-session and inter-session reliability study. SUBJECTS Twenty-five men (mean age 22.5 (standard deviation (SD) 1.7) years) were tested separately by 2 examiners using the resistance-enhanced dynamometer and a traditional hand-held dynamometer for an intra- and inter-examiner reliability study. Twenty-seven volunteers (mean age 22.1 (SD 0.8) years) were tested by a female examiner using the resistance-enhanced dynamometer for an intra- and inter-session reliability study. METHODS Maximum resisting forces for the knee flexors and extensors were measured using the resistance-enhanced dynamometer and the traditional hand-held dynamometer. RESULTS The traditional hand-held dynamometer had good intra-examiner reliability (intra-class correlation coefficient (ICC) = 0.79-0.93) but poor inter-examiner reliability (ICC = 0.11-0.28). The resistance-enhanced dynamo meter had very good intra-examiner (ICC = 0.91-0.94), inter-examiner (ICC = 0.98), intra-session (ICC = 0.93-0.99) and inter-session (ICC = 0.91-0.92) reliability. The resistance-enhanced dynamometer also had better inter-examiner agreement (smallest real difference (SRD) 9-16% for resistance-enhanced dynamometer, 21-43% for traditional hand-held dynamometer). CONCLUSION The resistance-enhanced dynamometer had very good reliability. Enhancing the examiner's resisting force appeared to improve the reliability of manual muscle strength measurements. The resistance-enhanced dynamometer is useful for muscle strength measurements in clinical practice.