Objective: 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. Methods: From October to December, 2017, 10 college students were recruited to participate in shoulder weight-bearing 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. Results: Weight and shoulder strap width had a significantly effect on fatigue (P<0.01) , and the change in the hardness of waist cushion had no significant effect on fatigue (P>0.05) . There was an interaction effect between weight and shoulder strap width (P<0.01) , and there was no interaction effect between weight, shoulder strap width, and hardness of waist cushion (P>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. Conclusion 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 weight-bearing walking is more likely to cause the fatigue of the erector spinae.

Objective: To investigate the influence of different variable combinations of the carrying system on gait and muscle fatigue during weight-bearing walking on both shoulders and back, and to optimize daily carrying experience. Methods: From September to December, 2018, 6 male college students were selected as subjects; the electromyographic signal of the anterior tibial muscle and plantar pressure were measured during weight-bearing walking under six different variable combinations of the carrying system (with the three variables of gravity center, single or double shoulders, and waist cushion), and a subjective evaluation test was performed for the degree of fatigue. The electromyographic data and plantar pressure data were processed and compared to evaluate behavior and fatigue. Results: Different variable combinations of the carrying system had significant influence on the degree of fatigue and gait (P<0.05). Both subjective and objective analyses found that the carrying system with different heights of gravity center and single-or double-shoulder carrying mode had great influence on human fatigue and walking gait, while the hardness of waist cushion had little influence. Compared with the other groups, the group with a high gravity center, a double-shoulder carrying mode, and a soft waist cushion had a significantly smaller slope of average electromyographic amplitude, a significantly larger slope of median frequency, and a significantly lower degree of plantar pressure curve disorder. Conclusion The carrying system with a relatively high gravity center, a double-shoulder carrying mode, and a soft waist cushion can significantly relieve fatigue, with low influence on walking gait.