Biomechanical responses following compelled forward versus backward body shift: How aging and perturbation direction...

Falls are a significant health risk in older adults, and forward and backward falls each account for more than 40 % of falls. Dynamic stability, limb support, and impact energy absorption are crucial balance regulatory components and likely vary with the direction of imbalance. Understanding how perturbation direction influences these key components of balance stability regulation is crucial. This study investigated the balance stability, lower limb impact energy absorption, and limb support in forward and backward directions of balance perturbations in younger versus older adults. Thirteen healthy old and thirteen healthy young adults participated in this study. Participants stood on two adjacent perturbation platforms in modified tandem stance. The leading or trailing limb support surface dropped 76.2 mm vertically at an unknown time to impose body shift. Two-way (direction X group) mixed ANOVA was performed to analyze the anterior margin of stability (MoS), trunk angular displacement, peak negative power at the hip, knee, and ankle, and the peak vertical ground reaction forces (VGRF). Compared to forward perturbation, backward perturbation induced greater MoS (P < 0.01), peak VGRF (P < 0.01), and peak ankle (P < 0.05) and hip (P < 0.05) joint power. Older adults showed decreased MoS (P < 0.05), perturbed limb peak VGRF (P < 0.05), and ankle (P < 0.05) and knee (P < 0.05) joint peak power compared to younger adults. Forward perturbations induced greater challenges for dynamic stability, possibly due to trunk motion characteristics, while backward perturbations posed challenges in limb support and impact energy absorption. In addition, age-related deficits in balance stability regulation were observed in both perturbation directions.