Effects of Age and Physical Activity on Adaptation of Kinematic and Spectral Gait Parameters to Optic Flow Perturbation

Background and aim: Advanced age is associated with an increased reliance on visual information to maintain walking balance, but physical activity (PA) may mitigate this dependence through the preservation of proprioceptive and vestibular function. In this study, we exploited large-scale virtual reality to examine whether age-related effects in responses to optic flow perturbation are modulated by PA.<br/><br/>Methods: Sixty participants (divided into four groups of 15: young active, young inactive, old active, and old inactive) walked for 14 minutes: 3 minutes of unperturbed baseline, 8 minutes with optic flow perturbations, and 3 minutes unperturbed. The participants walked through a virtual hallway displayed on a 180° semi-curved screen in front of the treadmill, which moved in the anteroposterior direction at a belt-speed-matched velocity. A mediolateral perturbation signal, composed of three sinusoids, was superimposed on the existing projection, to perturb the optic flow. Positional data was recorded from markers on the sacrum and heels, along with ground reaction forces, to measure step width (SW) and mediolateral margins of stability (MoS). <br/>To quantify whether the mediolateral body-sway was related to the perturbation signal, we computed the power spectral density (PSD) of the mediolateral movement of the sacrum marker and its coherence with the perturbation signal, both evaluated at the dominant frequency of the perturbation signal (0.250 Hz). To assess the interaction between age and PA on responses to optic flow perturbation, repeated measures ANOVAs were conducted: (1) comparing baseline (last 60 steps of baseline) and early perturbation (first 60 steps of perturbation), and (2) comparing early perturbation and late perturbation (last 60 steps of perturbation). Pairwise comparisons with Bonferroni correction were used when interaction effects were found.<br/><br/>Results: The optic flow perturbation initially elicited higher SW (36.8%), MoS (56.6%), and PSD (1022.5%) (all p&lt;0.001, figure 1). In addition, PA modulated age-related effects on PSD from baseline to early perturbation (p=0.026), as older active adults showed 136.2% higher PSD than older inactive adults (p=0.010), while young active and inactive adults did not differ. <br/>With prolonged exposure to the optic flow perturbation, SW and PSD decreased 11.9% and 43.1%, respectively, towards baseline levels (both p&lt;0.001). The effect of PA on PSD differed between age groups, with older active adults showing 92.7% higher PSD compared to older inactive adults (p=0.031). Again, young active and inactive adults did not differ. Furthermore, the coherence increased by 112.1% from early to late perturbation (p&lt;0.001) and inactive adults showed 4.8% higher coherence across phases compared to active adults (p=0.038).<br/><br/>Conclusion: These findings suggest that PA negates age-related declines in adapting to optic flow perturbations, highlighting its role in enhancing adaptive capacity across age groups.