Validity and reliability of a new isometric hand dynamometer

Two protocols were used to assess the reliability (Protocol 1) and validity (Protocol 2) of expansive force measured using a new hand-held dynamometer (model TSD121C). In Protocol 1 the dynamometer was calibrated at zero and spanned with a measured mass of 89.36 kg. Measured masses of 79.42, 49.41, 29.67 and 9.59 kg were suspended from the dynamometer and the values recorded. This loading procedure was repeated eight times per test, with the protocol being repeated on three separate occasions. For Protocol 2, the dynamometer was calibrated at zero and spanned with a measured mass of 9.59 kg. Measured masses of 9.59, 29.67, 49.41 and 79.42 kg were then suspended from the dynamometer and the values recorded. This loading procedure was repeated two more times. The entire procedure was then performed using different span masses of 29.67, 49.41, and 89.37 kg. Protocol 2 was then repeated on two further occasions.For Protocol 1, mean coefficients of variation (CV%) ranged from 0.4 to 0.8, whilst estimated confidence intervals (95% CI) for CV% did not exceed 1.2%. This showed that measurements of known actual mass using the new dynamometer were highly reproducible. Calculation of absolute and ratio 95% limits of agreement for data obtained in Protocol 2 showed that using a span mass of 0-29.67 kg provided the most accurate agreement between measured and actual values across the range of masses used in this investigation (bias of 0.99 and random error of ×/÷ 1.04). However, investigators should be aware of a random error of approximately 4% based on the limits of agreement.