The aim of this investigation was to examine the intra-subject and group reproducibility of isometric muscle function testing and the associated surface EMG signal repeated over five consecutive days using isokinetic dynamometry. Fifteen physically active volunteers that were unfamiliar with isokinetic dynamometry participated in this study and were asked to attend the laboratory on five consecutive days to complete maximal isometric testing. Surface electromyography was recorded from biceps brachii to examine the electrical activity associated with the peak torque. The intra-subject reproducibility was moderate for isometric torque (mean coefficient of variation (CV) of 6.65%), however the EMG and EMG:torque ratio were somewhat more variable (mean CV of 18.20% and 18.49%, respectively). The group reproducibility showed an intra-class correlation coefficient of r = 0.99, 0.92 and 0.96 for isometric peak torque, EMG and torque: EMG ratio. In addition, the group CV for isometric peak torque, EMG and torque:EMG ratio was 1.03%, 4.10% and 3.38%, respectively. Individuals can show large variations in torque and EMG, however when reproducibility is examined as a group both torque and the associated EMG activity have high reproducibility in physically active subjects, unfamiliarised with isometric dynamometry.