Validity and reliability of the BTE dynatrac

The BTE Dynatrac is an isotonic machine that measures isolated joint work and power at controlled constant loads. The purpose of this investigation was to: 1) assess the validity of the static and dynamic response characteristics, and 2) measure the within-tester reliability and between-tester objectivity of the Dynatrac. External force and position sensors were utilized to validate the Dynatrac. For the reliability and objectivity tests, 20 subjects each performed five power tests and one work test for each of four testers. Validity test results showed close agreement between the Dynatrac's position and velocity measures and those obtained from the external sensor. Moments reported by the Dynatrac underestimated those produced by the external force sensor. Within-tester reliability coefficients (ICC) for power variables averaged above 0.70. Between-tester ICC for power variables were all above 0.70 except for knee extension torques collected at 20 Nm. Between-tester ICC for work variables were all above 0.68, indicating a reasonable degree of objectivity. Based on results from these tests, the Dynatrac can be considered both reliable and objective. The measures of lever arm position and velocity were shown to be valid, while moment measures consistently underestimated expected results.