Objectives: Backpacks equipped with hip belts are among the most common and essential tools for carrying loads during long treks and mountaineering. The use of a hip belt facilitates appropriate load distribution between the upper and lower body and minimizes muscular energy expenditure. However, it may also restrict movement. This study aimed to examine the effect of three different hip belt designs in backpacks, namely 1) movable hip belt, 2) cross-frame structure, and 3) conventional design, on postural alignment control indices and center of pressure (COP) changes during standing and walking.
Methods: This semi-experimental study was conducted on 20 male physical education students aged 19 to 25 years. Three types of backpacks were used to measure postural control indices and COP changes: (1) backpack with a movable hip belt, (2) backpack with a cross-frame in the back panel, and (3) conventional backpack. Participants carried the backpacks on a level, flat surface with a standard load of 13 kg. A control walking test was also performed without any backpack under similar conditions. COP data in the anteroposterior (AP) and mediolateral (ML) directions were recorded at a sampling rate of 1000 Hz. The device was fully calibrated before the test. Data were processed using MATLAB software, and a Butterworth filter with a cutoff frequency of 10 Hz. Output variables, including COP path, COP area, velocity of COP (VCOP), and sway, were calculated using standard formulas and analyzed in SPSS software. The Shapiro-Wilk test was used to assess data normality. Repeated measures ANOVA was employed to compare the three backpack types, and Bonferroni post-hoc tests were used for pairwise comparisons.
Results: The results showed no statistically significant differences in terms of COP area during standing and walking among the different backpack conditions. In terms of COP displacement (P=0.009) and COP velocity (P=0.009), significant differences were found only during eyes-closed standing in the AP direction. Pairwise comparisons revealed a significant difference between the conventional backpack and the one with a movable hip belt. Regarding COP sway (P=0.030), a significant difference was observed among the three backpacks only during eyes-closed standing in the ML direction. However, no statistically significant differences were found between any two backpacks in post-hoc comparisons.
Conclusion: Based on the findings, the backpack with a movable hip belt was the most effective among the three designs, as it resulted in the lowest COP sway, COP velocity, and COP displacement. Furthermore, the impact of hip belt design becomes more apparent in tests with higher complexity. However, it is important to note that reduced COP sway does not necessarily indicate improved postural control or motor performance, and it may reflect a restriction in the responsiveness of the neuromuscular system.
