The maximum voluntary contraction and EMG amplitude of back and trapezius muscles were measured for every subject before driving. The EMG of investigated muscles was continuously recorded when driving and stored in PC for later analysis. The total length of each measurement was approximately 7 h, which included a half hour of preparation, 5 h driving with two short (5–15 min) breaks and from half to 1 h lunch break and another driving session of 1 h. The aver- age muscle activity measurements during driving were taken from the 3 h of driving after preparation. The muscle activity was assessed as a percentage of MVC.