Evaluation of the Load Reduction Performance via a Suspended Backpack with Adjustable Stiffness.

Backpacks are essential for travel but carrying a load during a long journey can easily cause muscle fatigue and joint injuries. Previous studies have suggested that suspended backpacks can effectively reduce the energy cost while carrying loads. Researchers have found that adjusting the stiffness of a suspended backpack can optimize its performance. Therefore, this paper proposes a stiffness-adjustable suspended backpack; the system stiffness can be adjusted to suitable values at different speeds. The stiffness of the suspended backpack with a 5-kg load was designed to be 690 N/m for a speed of 4.5 km/h, and it was adjusted to 870 and 1050 N/m at speeds of 5.5 and 6.5 km/h, respectively. The goal of this study was to determine how carrying a stiffness-adjustable suspended backpack affected performance while carrying a load. Six healthy participants participated in experiments where they wore two backpacks under three conditions: the adjustable-stiffness suspended backpack condition (S_A), the unadjustable-stiffness suspended backpack condition (S_UA), and the ordinary backpack condition (ORB). Our results showed that the peak accelerations, muscle activities, and peak ground reaction forces in the S_A condition were reduced effectively by adjusting the stiffness to adapt to different walking speeds; this adjustment decreased the metabolic cost by 4.21 ± 1.21% and 2.68 ± 0.88% at 5.5 km/h and 4.27 ± 1.35% and 3.38± 1.31% at 6.5 km/h compared to the ORB and S_UA, respectively.