## 3 Results
These results suggest that while older adults responded to VGRF biofeedback by increasing knee flexion during swing and loading response, their knee position remained relatively unchanged during the first half of the stance phase. Additionally, the lack of change in hip flexion angle indicates that they maintained their usual hip mechanics, suggesting a localized effect of the biofeedback on knee mechanics rather than a broader alteration in gait strategy. Figure 5: The first peak of the vertical ground reaction force across time points. The red triangles are the mean values with error bars showing standard error. Asterisks (*) indicate significant differences compared to baseline walking, \(p<0.05\). Figure 6: Peak knee flexion angle (**A**) and peak hip flexion angle (**B**) during the first half of the stance phase of walking across time points. The red triangles are the mean values with error bars showing standard error. Asterisks (*) indicate significant difference from baseline walking, \(p<0.05\). The green dots are the participant (#15) who has been identified as an outlier during baseline and recall 1 for knee flexion angle. There was a significant main effect of time point on peak knee extension torque (F3,36 = 9.79, \(p\) < 0.001). The peak knee extension torque was greater during the acquisition and recall 1 trials than baseline (_p_ < 0.05 for all comparisons; Figure 7A). No significant main effect was observed for hip extension torque (_p_ = 0.44; Figure 7B). Additionally, there was a significant main effect of time point on the percentage of knee extension torque contribution (F3,36 = 10.67, \(p\) < 0.001; Table 1), with higher percentages during acquisition and recall trials compared to baseline (_p_ < 0.05). This suggests that VGRF biofeedback effectively increased knee extension torque during walking, with sustained effects observed in recall trials. The improvement persisted even after a short break, although the statistical significance in recall 2 was dependent on the exclusion of an outlier. In contrast, hip extension torque remained unchanged, indicating that participants did not compensate by increasing hip involvement. Furthermore, the increased percentage of knee extension torque contribution suggests a shift in joint-loading strategy, with a greater reliance on knee extensions rather than hip extensors, potentially mitigating age-related distal-to-proximal torque redistribution. Our analysis identified an outlier in knee flexion angle during the baseline and recall 1 trial, represented by a green dot in Figure 6A. The inclusion or exclusion of this outlier did not affect the overall results for most variables. However, for knee extension torque during recall 2, the significance of the difference from baseline was shown only after excluding the outlier. There was a significant main effect of time point on maximum EMG of VL (F3,36 = 4.02, \(p\) < 0.05; Figure 8A) and GMAX (F3,36 = 6.26, \(p\) < 0.05; Figure 8B). Post hoc comparisons show that older adults increased their VL and GMAX muscle activities during acquisition and recall trials compared to baseline walking (_p_ < 0.05), with no difference between acquisition and recall trials. These results showing that increasing the first peak of VGRF led to a greater activation of both knee and hip extensor muscles suggest an adaptive response to generate higher vertical support forces during walking. A significant difference was found in overground comfortable walking speed before (1.35 \(\pm\) 0.31) m/s or 4.86 \(\pm\) 1.12 km/h) and after (1.46 \(\pm\) 0.24 m/s or 5.26 \(\pm\) 0.86 km/h) a single session of biofeedback walking (t = \(-\)2.52, df = 12, \(p\) = 0.02), but no difference was observed for overground faster walking speed. Figure 7: Peak knee extension torque (**A**) and peak hip extension torque (**B**) during the first half of the stance phase of walking across time points. The red triangles are the mean values with error bars showing standard error. Asterisks (*) indicate significant difference from baseline walking, \(p\) < 0.05.