Inertial Motion Capture of Sagittal Kinematics Reveals Compensatory Strategies for Forward Loss of Balance in...

Improving the ability of visually impaired (VI) people to react quickly to daily falls is crucial. However, it is not clear whether long-term vision impairment leads to unique reactive balance strategies compared with those with visually healthy (VH). To examine whether the lower-limb compensatory strategies identified through wearable sensor-based biomechanical analysis in the sagittal plane are distinctive and measurable in VI individuals responding to postural perturbations.

This study was conducted from August 2023 to October 2024. A total of 13 VI individuals and 13 age-matched VH controls were recruited. High-precision IWS inertial sensors were used to collect kinematic data from the pelvis, hip, knee, and ankle joints during balance perturbations. The joint motion responses were divided into the perturbation phase and the response phase. Key parameters analyzed included peak angles, angular displacement, time to peak angle, response time, response velocity, and inter-joint coordination (e.g., pelvis/hip, pelvis/ankle, and hip/ankle angular displacement ratios) during both phases. Between-group comparisons were performed using independent samples t-tests, with the significance level set at α = 0.05.

While the lower limb joint movement trajectories of VI and VH showed overall similarity, significant intergroup differences emerged in key kinematic parameters. During the perturbation phase, the VI demonstrated significantly shorter peak ankle plantar flexion and pelvic anteversion durations, indicating more abrupt initial compensatory strategies. In the reaction phase, they exhibited markedly greater joint mobility at the pelvis, knee, and ankle joints, accompanied by significantly prolonged response times for the pelvic and ankle joints. Additionally, their hip, knee, and ankle joint response rates were notably slower, with significant differences in the response angle displacement ratios between the pelvic/hip and pelvic/ankle joints. These findings collectively reflect the lower efficiency of VI in restoring overall stability following balance perturbations.

This study demonstrates that individuals with visual impairment employ kinematically distinct and measurable compensatory strategies in the lower limbs when responding to sagittal plane postural perturbations. These results substantiate the use of wearable sensor-based biomechanics for objectively evaluating balance recovery strategies in visually impaired populations, providing a foundation for future interventions aimed at fall prevention.