Development, reliability and validity of a new motorized isometric dynamometer for measuring strength characteristics...

The aim of this study was to develop a new apparatus capable of accurately recording and analysing torque-time curve during isometric muscle contractions of the elbow flexors. A total of 25 (age 29.3+/-5.0 years) non-athlete male volunteers participated in this study. To establish the measurement precision of the new testing apparatus and to determine possible sources of error in the results, a series of tests was performed. Instrument validity was assessed by comparing each selected measure (lever arm angular position, torque and maximal isometric torque) to a criterion (external inclinometer, calibrated weights and isokinetic dynamometer, respectively), while trial-to-trial and day-to-day comparisons of measurements were made to estimate the reproducibility of the instrument. The statistical outcomes of validity tests demonstrated high agreement between measures and associated criteria (Pearson correlation coefficient's values >.97). Trial-to-trial correlations for maximal isometric torque in different elbow angles showed excellent reproducibility, as values of intraclass correlation coefficient (ICC([2,1])) ranged from 0.889 to 0.971, with higher value in the middle angle (90 degrees ). The value of ICC([2,1]) (day-to-day) for maximal isometric torque in 90 degrees was 0.986 and the respective standard error of measurement (SEM) was 1.5 Nm. Our results indicate that the isometric evaluation of elbow flexor muscles with the new dynamometer is accurate and reproducible.