Surface electromyography has been useful in comparing muscular activity among different sports movements and it is a valuable technique for evaluating muscle activation, co-ordination and fatigue. Since these important variables have not been investigated during the full game in soccer, the present study aimed to investigate the activity of major muscles of the lower extremity during a soccer-simulation fatiguing protocol. Ten amateur soccer players (age 21.40+/-3.13 years; height 1.77+/-0.06 m; mass 74.55+/-8.5 kg) were tested. The exercise protocol, performed on a programmable motorised treadmill, consisted of the different intensities observed during soccer match-play (walking, jogging, running, sprinting). Electromyographic activity was recorded from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius (GC) muscles before exercise, at half-time and immediately after the 90-min exercise protocol. The EMG data were analysed using custom-written software to compute the root mean square (RMS) value over ten gait cycles. With regard to RF, BF and TA, a significant main effect (P< 0.05) was found for condition (pre-game, half-time and post-game), speed (6, 12, 15 and 21 km h(-1)) (P<0.05) and interaction between condition and speed (P< 0.05). For GC, a significant effect was not found for condition or interaction between condition and speed, but a significant main effect (P< 0.001) was found for speed, with the RMS value increasing continually with increasing speed from 6 to 2 1km h(-1). The results indicated that after a simulation of the exercise intensity of soccer-play the EMG activity in major lower-limb muscles was less than before. This decrease indicated that prolonged intermittent exercise had an effect on muscle activity even when work-rate was sustained.