The reproducibility of peak isokinetic torque and EMG activity in unfamiliarised subjects on repeated days

The aim of this investigation was to examine the intra-subject and group reproducibility of isokinetic muscle function testing and the associated surface electromyography (EMG) signal on repeated days testing. Fifteen subjects who were unfamiliar with isokinetic dynamometry completed maximal isokinetic elbow flexor contractions at 60 degrees/s and 210 degrees/s on five consecutive days. Surface electromyography was recorded from the biceps brachii to examine the electrical activity associated with the peak torque. The intra-subject reproducibility was moderate for isokinetic torque: mean coefficient of variation (CV) of 8.93% at 60'/s and 9.14% at 210 degrees/s, however the EMG and EMG:torque ratio were somewhat more variable: mean CV of 15.18% and 18.42% at 60 degrees/s, respectively and 11.97% and 14.50% at 210 degrees/s, respectively. The group reproducibility for all variables at both isokinetic speeds were high with intraclass correlation coefficients ranging from 0.92 and 0.99. In addition, the group CV for isokinetic peak torque, EMG and EMG:torque ratio for both contraction speeds ranged from 1.47% to 5.12%. These results illustrate that individual subjects can show large day-to-day variations in torque and EMG, however when group data are examined, both torque and the associated EMG activity demonstrate high reproducibility. Practitioners should therefore express caution when interpreting longitudinal changes in an individual's isokinetic data.