Perceived Fatigue Evaluating Model in Health Men Performing Backpack Load-Carriage Exercises

Objectives This study aimed to develop a fatigue model for human load carriage during endurance exercise using quantification of perceived pains and physiological parameters. Methods Heart rate, skin contact pressure, and perceived pains and corresponding locations of five healthy participants were measured during treadmill tests on non-consecutive days under three different conditions of backpack payloads (29, 31.5, and 34 kg). Results All participants could complete the trials without resting using 29, 31.5, and 34 kg payloads for 50 min. The slopes for heart rate regression equations in three-payload conditions became steeper as the payload increased. The trends of root mean square (RMS) of skin contact pressure in back, shoulder, and hip regions are all changing smoothly. But the overall amplitudes of RMS of pressure in shoulder region in all three-payload conditions are higher comparing with other two regions. Perceived fatigue intensity results showed that shoulder region was the most discomfort region on the body and was highest using 34-kg payload. Conclusions The results suggested that shoulder fatigue may limit endurance performance, thereby indicating the importance of a well-designed shoulder strap. A fatigue intensity predictive model was proposed to allow prediction of human load carriage limits and fatigue intensity trend for endurance exercise.