The effect of velocity and familiarisation on the reproducibility of isokinetic dynamometry

BACKGROUND: The reproducibility of the HUMAC-NORM isokinetic dynamometer has not yet been established for the muscles around the knee. Previous research suggests practice-based improvement (PBI) may impact upon the reproducibility of isokinetic testing. OBJECTIVE: To investigate test-retest reproducibility of knee flexion and extension isokinetic findings at different velocities, including the influence of familiarisation. METHODS: Seventy physically active, healthy participants with no experience in isokinetic dynamometry performed five repetitions of continuous concentric knee flexion and extension at 60, 120, 180 and 240 degrees/s on four occasions. Peak moment, angle of peak moment, total work and average power were recorded. Reproducibility was determined using percentage change in the mean, typical error and intraclass correlation coefficients (ICC). RESULTS: For knee flexion and extension, group data met desirable reproducibility criteria for most outcomes and velocities after Trial 2. Within-subject reproducibility generally met acceptable reliabilty criteria after Trial 2 for knee extension, but was predominantly unacceptable for knee flexion. ICC's were acceptable from Trial 2, except for angle of peak moment which did not achieve an acceptable level of reliabilty across any trials, outcomes or velocities. CONCLUSIONS: The HUMAC-NORM demonstrates excellent reproducibility for peak moment, average power and total work parameters for the major knee muscles after one trial. One familiarisation session is recommended prior to testing to minimise the impact of PBI. Additional familiarisation is beneficial when testing individuals, higher velocities and knee flexion.