Hand-held dynamometry: tester strength is paramount, even in frail populations

To determine test-retest and inter-rater reliability of hand-held dynamometry when used to measure knee--extensor strength in patients with advanced cancer.

Adults with metastatic or locally advanced cancer recruited from palliative care services to a study of the risk factors for falls.

Consecutive recruits (n = 30) underwent repeat testing after an interval of 1 h, by the same researcher, to assess test-retest reliability. The subsequent 15 patients underwent retesting by a second researcher. The intra-class correlation coefficient and limits of agreement were calculated.

The test-retest reliability difference between measurements increased with the magnitude of measurement, mean leg strength = 113 N (standard deviation 43.1), 95% ratio limits of agreement 0.81-1.5, intra-class correlation coefficient = 0.9. The inter-rater testing mean leg strength = 128.5 N (standard deviation 35.1), 95% limits of agreement = -57.24 to 36.06 N. Intra-class correlation coefficient = 0.83.

Test-retesting and inter-rater testing yielded high intra-class correlation coefficients, but the limits of agreement were wide. In test-retesting, the difference between tests increased as the magnitude of measurement increased. It has been widely reported that hand-held dynamometry is reliable when used to measure knee-extensor strength in frail or elderly persons. However, our results show that, even in these populations, reliability may be compromised by inadequate tester strength.