Impact of age and slope angle on the motion between the body's center of mass and center of pressure during downhill walking

INTRODUCTION: Downhill walking increases fall risk in older adults due to greater balance control demands and postural instability. Steeper inclines amplify gravitational shear forces, requiring precise lower limb coordination to maintain stability. This study investigated the effects of age and slope angle on COM-COP inclination angles (IAs) and rates of change of inclination angles (RCIAs) to better understand age-related adaptations in balance control. MATERIALS AND METHODS: Fifteen young and fifteen older adults walked at self-selected speeds on level ground and three downhill slopes (5°, 10°, and 15°). Motion capture and force plates recorded gait parameters, from which IAs and RCIAs were calculated. Analysis of covariance (ANCOVA) was used to control for walking speed variations and assess age and slope effects. RESULTS: As ramp-down angles increased, both groups exhibited reduced walking speed, step length, and single-limb support duration, while double-limb support duration increased. After adjusting for walking speed, significant slope effects were observed for sagittal IA and RCIA at toe-off, as well as for sagittal and frontal RCIA at contralateral heel-strike. Older adults exhibited significantly higher frontal IA and RCIA at contralateral heel-strike, suggesting increased lateral postural demand. These changes may reflect a compensatory effort to maintain stability. CONCLUSION: Older adults rely on conservative gait strategies but experience greater lateral instability at contralateral heel-strike, increasing fall risk. These findings highlight the need for targeted balance training and infrastructure modifications to improve safety on sloped surfaces.