The effects of age and physical activity level on spatiotemporal gait parameters under optic flow perturbations in healthy adult walking

With advancing age, the quality of sensory information declines, leading to reweighting of the different sensory inputs. Following the sensory reweighting hypothesis, older adults rely more on visual feedback to control their gait. In addition, the results on sensory reweighting might also be confounded by physical activity level as well as gait speed and reflected in gait parameters such as step length, step width and their variability. Here, we investigated the effects of mediolateral optic flow perturbation in groups of younger and older adults that were either inactive (N=10 younger and N=11 older) or active (N=11 younger and N=8 older). Participants walked for 14 minutes on an instrumented treadmill at three different speeds (slow: 0.6 and 0.5 m/s; intermediate: 1.2 and 1.0 m/s; fast: 1.8 and 1.5 m/s for younger and older adults, respectively) that were normalized for leg length. At each speed, participants started walking for three minutes without perturbation (baseline) followed by eight minutes under mediolateral optic flow perturbations(perturbation) and finished with three minutes without perturbation(post-perturbation). The order of the speeds was randomized between subjects. A motion capture system (VICON) with ten cameras was used to record sacrum as well as bilateral heel 3D marker positions. From these data, step length and step width as well as their variability were calculated to evaluate changes in spatial gait parameters as a result of mediolateral optic flow perturbation. Preliminary results indicate that mediolateral optic flow perturbation resulted in smaller step lengths, larger step widths as well as higher step length and step width variability as compared to baseline in all groups. In the eight minutes of perturbation, the results suggest that participants are able to adapt to the optic flow perturbation indicated by the spatial gait parameters gradually returning to the direction of baseline. Moreover, physical activity level did not affect gait kinematics in younger adults, but active older adults had smaller step lengths and larger step widths at intermediate and high speeds than inactive older adults. Both step length variability and step width variability decreased with increasing gait speed in the four groups. In conclusion, our findings indicate that optic flow perturbation affects gait parameters in both younger and older adults. Furthermore, the preliminary results suggest that gait adaptation was mediated by walking speed, with changes in gait parameters being more pronounced at lower walking speeds. Altogether, these findings provide insights into how the control of gait is affected by optic flow perturbations in people of different age groups and levels of physical activity. Further work can be done by dividing age and physical activity level into more groups to find more detailed changes by ageing and the dose-response between physical activity and gait parameters.