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.

Stability control in older adults with asymmetrical load carrying when stepping down a curb.

We investigated the effect of asymmetric load carrying using different bag types with the dominant and non-dominant hands on upper limb coordination, walking adaptations, and stability control in a curb-descend task in older adults. Fourteen participants walked on a pathway with a 16-cm curb located in the middle. They walked without a load or asymmetrically carrying a load corresponding to 7% of their body mass. The weight was placed in two different bags (with and without strap) and carried by the dominant and non-dominant hands. The upper limb coordination analysis showed that the anti-phase pattern between right and left shoulder reduced considerably due to the almost motionless shoulder of the side carrying the load. The spatial-temporal walking parameters and curb negotiation variables were unaffected by load carriage. The margin of stability (MoS) was unchanged by load transportation in the AP direction. In the ML direction, taking the bag on the same side of the foot contacting the floor increased the MoS; however, when the load was incorporated into the COM model, the MoS did not differ anymore from the control condition. The changes in interlimb coordination reflected a strategy to prevent unexpected movements of the bag that could threaten body stability. Healthy older adults were able to predict the consequences of carrying a load and kept the MoS constant. They compensated for the disturbance caused by the transport of a relatively moderate load and performed the descending curb task successfully.

Additional Haptic Information Provided by Anchors Reduces Postural Sway in Young Adults Less Than Does Light Touch.

This study investigated the effect of adding haptic information to the control of posture, as well as comparing the effect of both the "light touch" (LT) and "anchor system" (AS) paradigms on postural sway. Additionally, it compared the effect of location and number of points of contact to the control of posture in young adults. The location consisted of using the anchors tied to the finger and held by the hands, and, for LT, the fingertip. For the number of points of contact, participants used two hands, and then separately the dominant hand, and the non-dominant hand, for both anchor and LT paradigms. Participants stood upright with feet-together and in tandem position while performing tasks that combined the use of anchors and LT, points of contact (hand grip and finger), and number of points of contact (two hands and one hand). In this study, the anchors consist of holding in each hand a flexible cable with the other end attached to the ground. The LT consists of slightly touching a rigid surface with the tip of the index finger. The results showed, first, that the anchors improved postural control less than did the LT. Second, they revealed that holding the anchors with the hands or with them tied to the fingertip resulted in a similar reduction in postural sway only in the tandem position. For the feet-together position, the anchors tied to the fingertip were ineffective. Similarly, the use of one or two hands did not affect the contribution of the anchors. However, using two hands in the LT condition was more effective than was one hand. Third, our results showed the presence of a temporal delay between force and center-of-pressure (COP) for the anchors, only in the AP direction with feet-together. In conclusion, overall, the anchors were less effective in reducing postural sway than was the LT. The anchors attached to fingertips were as effective as the hand-held anchors in the tandem position, yet ineffective during foot-together standing. Force-COP timing explains reduced postural sway with LT but not for the anchor; hence, exploratory and supra-postural components may be involved.