AbstractThe aim of this study was to investigate the relationship between the electromyographic activity (EMG) of dynamically or statically working and nonworking muscles and blood lactate concentrations during progressive exercise in seven endurance-trained and seven speed-trained male athletes. Blood lactate concentrations during the incremental exercise showed a high correlation with EMG not only in dynamically loaded antagonists (m. rectus and biceps femoris) and m. soleus, but also in nonworking muscle (m. frontalis). No relationship was found between EMG and blood lactate in statically loaded m. trapezius. The nonlinearity in EMG versus the progressively increasing power output curves was observed in dynamically working leg muscles and nonworking m. frontalis, but not in m. trapezius. The nonlinear increase in EMG, which can be the EMG threshold, occurred within the range of exercise intensities corresponding to the individual anaerobic threshold and the anaerobic threshold at the blood lactate level of 4 mmol .I-1(4 mM-AT). The EMG threshold for m. soleus, rich in slow-twitch fibers, was found just at the individual anaerobic threshold in both the endurance- and speed-trained groups. On the contrary, the EMG threshold for m. rectus f., which is mainly composed of fast-twitch fibers, approximated the anaerobic threshold at a blood lactate level of 4 mmol . I-1, especially in endurance-trained athletes. The results indicate that the EMG threshold reflects the threshold pattern in blood lactate accumulation during progressive exercise in endurance- as well as speed-trained athletes. Therefore, it may serve in sports medicine practice as a useful, noninvasive measure of anaerobic threshold.