Gait control to step into a lowered surface with one limb with different demands for accuracy in younger and older adults.

Walking in a daily life context requires constant adaptations to meet the environment's requirements for successful locomotion. We investigated the walking adaptations of younger and older adults when dealing with holes of different lengths in the pathway (60-cm long and 1.3 times foot length [critical point] conditions). We used the critical point condition to increase the demand for accuracy as it reduces the safety margin between the foot and the borders of the hole. Fifteen younger and fifteen older adults walked barefoot on a wooden walkway in three conditions: no-hole, 60-cm hole (length: 0.60 m | width: 0.80 m | depth: 0.095 m), and critical point hole (length: participant's foot length × 1.3 | width: 0.80 m | depth: 0.095 m). Participants stepped into the hole with only one foot. We assessed the impulses based on the ground reaction forces, trunk and lower limb joint angles, stride speed, and the margin of stability based on the concept of the extrapolated center of mass in the sagittal plane. Across walking conditions, older adults exhibited a larger margin of stability than younger adults. Before the hole, both age groups increased the braking impulse and adopted a more flexed posture of the lower limbs to help to lower the body in the subsequent step. Only older adults increased the vertical braking impulse and markedly reduced stride speed when stepping into both holes. Both age groups adopted a more vertically oriented trunk posture as a strategy to contribute to stability control when stepping into the hole. The two age groups showed a larger margin of stability and a more flexed trunk posture after the hole than the no-hole condition. Older adults were able to control body stability adequately and even better than younger adults. Younger and older adults used the same anticipatory and compensatory locomotor adjustments before and after the hole. These adjustments resulted in improved stability control. The differences between younger and older adults were confined to the moment of stepping into the hole. Older adults used a more cautious strategy that ensured task accuracy and gait progression.