The study consisted of two parts. In part one the load on the back and muscle fatigue in bimanual symmetrical lifting from floor to table were studied in a lifting experiment of 1 hour' s duration. The following weights and lifting frequencies were used. 10% of max. lifting capacity (MLC) 6 and 15 times per min, 25% MLC 5 and 10 times per min and 50% MLC 3 and 6 times per min. The EMG mean amplitude from the back muscles (L3) showed that even light burdens (10 kg) cause considerable back-toads equivalent to 40–50% MVC. When lifting 50 kg burdens short lasting backloads near the MVC were present. Mean amplitudes and mean spectral frequencies of the EMG were in general increasing, respectively decreasing, as the lifting experiment progressed. Such changes in the EMG are normally interpreted as muscle fatigue caused by changes in the concentration of the chemical substances from the muscle. The EMG changes are most pronounced when lifting 50% MLC (6 times per min) and 10% MLC (15 times per min) and are to a ...