Analysis and modeling of fatigue during weight-bearing walking

The objective of this study was to discuss the mechanical characteristics and distributed regularity of shoulder, waist and back of the human body through the experiment of weight-bearing walking; to establish the dynamic fatigue model based on stress regularity to provide a reference for the task design of weight-bearing walking and the ergonomics simulation of backpack. Thirteen healthy people participated the experiment that was recruited by internet and they were all men. Every subject made a 21 min weight-bearing walking on the treadmill with the speed of 5 km/h and a 15 kg load. The pressure data of their shoulder, back and waist was collected by pressure measuring system and the feeling of fatigue of the above three body parts of the subjects was asked every 3 min by using Borg scales. The results showed that the force of the subjects’ left shoulder and right shoulder was different and the force was higher on one shoulder while it was lower on another shoulder. The stress regularities of waist and back were similar to the shoulders and it was higher on left side of some subjects while it was higher on right side of other subjects. Also the stress on waist and back was different. The stress on shoulder was much higher than it was on waist and back while the stress on back was the lowest. The impulse was calculated based on the stress data of three body parts. The model was established based that the impulse was as dependent variable and the feeling of subjects’ fatigue was as independent variables. It showed a strong linear relationship between the pressure impulse of the three body parts and the feeling of subjects’ fatigue. The subjects’ fatigue could be well predicted during weight-bearing walking by using the linear model of impulse and subjective fatigue. So the conclusion of this study can be made that the stress on shoulder, back and waist is not asymmetric and it was great difference on the body three parts. The shoulder is not only the main bearing pressure part, but also the easiest part of fatigue. The fatigue can be well predicted during weight-bearing walking by the linear model that combine impulse and the feeling of subjects’ fatigue.