We carried out study on surface electromyogram (sEMG) signal generated from cluster muscles in trunk and lower limbs on condition of human body walking with heavily burdened shoulder to explore functional status and fatigue property of human muscles and to offer an important reference for finding better ways of loading, improving the performance and design of backpack as well as weight-bearing system more suitable for ergonomics. We measured and obtained surface electromyography signals from the primary muscles clusters in neck, shoulder, back and leg of 20 test recipients loaded with different burdens on their shoulders. The eigenvalue of mean power frequency (MPF) were processed with SPSS 16.0. It could be concluded that with the increase of loading weights, male are more likely to be fatigued due to dramatic decrease of trapezius' MPF. While for the female test recipients, the cervical extensor muscles' MPF dropped significantly and were more easily fatigued. Moreover, there was a remarkable difference in terms of electromyography signal before and after the weight reaches certain limit (P<0.05) . The maximum weight limit loaded on shoulders for man is 12% of the total bodyweight while such limit for woman is just 9%.