## 4 Discussion  
This study determined the short-term effects of real-time force feedback on hip and knee joint kinetics, kinematics, and extensor muscle activities. Our findings support our primary hypothesis that older adults increased their peak VGRF during loading response, with greater knee extension torque and knee extensor muscle activity during biofeedback and recall trials compared to baseline walking. In contrast, compared to baseline walking, older adults did not demonstrate an increase in their hip extension torque during biofeedback or recall trials. These results suggest that older adults can use biofeedback to increase the knee extension torque and generate vertical forces without increasing the contribution from the hip extension torque. In the clinic, wearable shoe sensors could be used to provide real-time feedback, encouraging older adults with reduced VGRF to improve force generation and enhance knee extensor engagement, potentially improving mobility. In our study, older adults walked at a constant speed of 1.2 m/s across all conditions. This speed falls within the range of preferred walking speeds for older adults [12; 30]. We observed that they walked with a higher cadence during biofeedback and recall trials without changing step length. We report the group average results for cadence and step length, rather than individual steps. The statistical significance of each variable was influenced by the mean differences and standard deviation (variability). It is possible that, because the variability in cadence is lower compared to step length, ANOVA was able to detect significance in cadence but not in step length. Participants increased their first peak of VGRF by an average of 15.45% from baseline to acquisition, 12.27% in recall 1, and 19% in recall 2 trials. Consistent with previous studies [27; 31], we showed that the biofeedback was effective in increasing the first peak of VGRF not only during the acquisition phase but also during recall trials, reflecting the short-term retention of the learned response. In addition, overground comfortable walking speed was increased after the single session biofeedback exercise, suggesting that limb loading could affect forward progression and that VGRF biofeedback has the potential to increase walking speed. Only one participant showed an increased VGRF, by 2.9%, during acquisition and did not show an increase during recall 2, possibly due to fatigue or recall difficulty. This highlights the need to consider individual variability and suggests that some participants may require additional rest or different strategies to maintain the learned behavior. Figure 8: Group average of normalized electromyography during the stance phase of walking across time points: (**A**) vastus lateralis (VL), (**B**) gluteus maximus (GMAX). Asterisks (\(\lx@paragraphsign\)) indicate significant difference from baseline walking, \(p<0.05\). Analysis of knee and hip joint angles and torques demonstrated patterns consistent with previous research [9; 32]. Hip and knee flexion were observed after foot contact, with peak hip and knee extension torque to stabilize the leg and support the body's weight. Knee extension torque increased during biofeedback and recall trials by an average of 73.7% relative to baseline walking. A previous study on knee extension torque biofeedback demonstrated that targeting a 40% increase in peak knee extension torque during early stance resulted in a 9% increase in vertical ground reaction force (VGRF) [33]. There are pros and cons to using knee extension torque biofeedback compared to VGRF biofeedback. One key challenge of knee extension torque biofeedback is the complexity of real-time computation, as it requires a precise marker-based model and intricate biomechanical calculations. Additionally, participants may struggle to interpret knee extension torque feedback effectively.