Reproducibility of isokinetic ankle dorsiflexor strength and fatigue measurements in healthy older subjects

Abstract

The aim of this study was to determine the test-retest (two occasions seven days part) reproducibility of isokinetic (Biodex) concentric (CON) and eccentric (ECC) ankle dorsiflexor strength and fatigue measurements in older subjects using several statistical methods. Thirty healthy men (n=15) and women (n=15) aged between 70 and 85 years participated in the study. To determine the reproducibility of strength measurements, the 30 individuals performed three maximal CON and ECC contractions at 30°/s and 90°/s. The intraclass correlation coefficient (ICC_{2.1}) for CON and ECC strength measurements was high and ranged from 0.94 to 0.98. Bland & Altman graphs and analyses indicted no systematic bias. The standard error of measurement (SEM), representing the smallest change that indicates a real improvement (or deterioration) for a group of individuals, was small ( 0.94) between CON peak torque at 30°/s and 90°/s, as well as ECC peak torque at 30°/s and 90°/s, suggested that any of these two velocities could be used as a reference. To determine the reproducibility of fatigue measurements, 28 of the 30 individuals performed 50 maximal CON contractions at 60°/s. Reproducibility of the loss in work (work fatigue) and the relative loss in peak torque, comparing the first three to the last three contractions (3-3), was determined and the ICC was 0.71 and 0.60, respectively. In addition, the SEM was small (< 8.4%) and the 'error bands' to define the SRD for a single subject were also small (from −23.5% to 24.5%). In conclusion, these values indicate small measurement errors and thus provide a clinically acceptable basis for testing ankle dorsiflexion strength and fatigue of the dominant side in healthy older people. (Less)