[Research on the influence factors of the carrying system].

To investigate surface electromyography signal (sEMG) of the major back muscle group and subjective fatigue assessment under different experimental combinations during walk with weight on both shoulders, as well as the functional status and fatigue property of human muscles. From October to December, 2017, 10 college students were recruited to participate in shoulder weightbearing work and walk under the combinations of different shoulder strap widths, weights, and hardness of waist cushion. The subjects were required to complete 12 sets of experiments, with each set lasting for 15 minutes, and the rest time between work was 30 minutes. The sEMG signals of the upper trapezius and the erector spinae were measured during the experiment, and subjective fatigue assessment was performed during rest. The time domain evaluation index (average amplitude, aEMG) , the frequency domain evaluation index (median frequency, MF) , and the data of subjective assessment were processed and analyzed. Weight and shoulder strap width had a significantly effect on fatigue (<0.01) , and the change in the hardness of waist cushion had no significant effect on fatigue (>0.05) . There was an interaction effect between weight and shoulder strap width (<0.01) , and there was no interaction effect between weight, shoulder strap width, and hardness of waist cushion (>0.05) . For the backpack carrying system, the combination of 10% weight and 50 mm shoulder strap width was the best one for relieving fatigue. The subjective test also showed that subjective feelings of muscle fatigue were associated with the weight and width, which was consistent with sEMG results. The results of this experiment show that the combination of 10% weight and 50 mm shoulder strap width can help to relieve muscle fatigue during walk with weight on both shoulders, and weightbearing walking is more likely to cause the fatigue of the erector spinae.