The purpose of this study was to examine the effects of delayed-onset muscle soreness after a strength-training session on the motor performance of the upper extremities, including the reaction time, speed of movement, tapping speed and coordination. In addition, muscle strength, electromyographic (EMG) activity, creatine kinase (CK) and soreness responses were measured. The study was a randomised cross-over intervention study, where 30 subjects (divided into two groups, A and B) performed a 1-h muscle strength-training session of the upper extremities, and the responses were measured 48 h after that. All of the subjects experienced muscle soreness, which was evaluated on a visual analogue scale. The mean value of CK activity was 115 IU.l-1 before training and 1259 IU.l-1 after training (P < 0.001). There were no statistically significant differences in wrist flexion/extension muscle strength or EMG tests in either group. Isometric elbow extension strength decreased by 4% (P < 0.01) in group A, and elbow flexion strength decreased by 6% (P < 0.05) in group B. There were no statistically significant changes in simple reaction time, choice reaction time, or speed of movement or coordination in either group. However, tapping speed decreased by 2% (P < 0.05) in group A and by 6% (P < 0.001) in group B. Based on the results of this study, it seems that the feeling of incompetence to perform fast and accurate movements with sore muscles is mainly a subjective feeling, and it may be that the real effect of muscle soreness on motor performance is quite small, and presumably less than generally assumed.