This study aimed to assess the effect of real-time vertical ground reaction force (VGRF) biofeedback on sagittal plane hip and knee joint biomechanics and extensor muscle activities in older adults. Fifteen healthy older adults (71 ± 5.8 years) walked on a treadmill while instructed to increase their first peak of VGRF via biofeedback. Whole-body kinetic and kinematic data and electromyography data for the vastus lateralis and gluteus maximus muscles were recorded. A one-way repeated measure ANOVA followed by post hoc analysis was conducted. Results showed increases in peak VGRF (20.95%), knee extension torque (73.7%), knee flexion angle (53.8%), and vastus lateralis muscle activity (72.1%) during the loading response, with percentage changes calculated as the mean of acquisition and recall trials relative to baseline walking. In contrast, no significant effect on peak hip extension torque and hip flexion angle over time was observed. These findings suggest that biofeedback can induce greater vertical support forces production with increased knee extension torque and extensor muscle activity. In addition, older adults adopted higher vertical support without increasing hip joint torque, potentially aiding in mitigating age-related distal-to-proximal joint torque redistribution. These findings suggest that VGRF biofeedback could potentially be an effective intervention to enhance knee extensor activation and mobility in older adults without increasing hip load.

Balance perturbations are often used to gain insight into reactive control strategies used to prevent falls. We developed a Perturbation Platform System (PPS) that can induce perturbations in both vertical and angled directions. The PPS was evaluated using human subject testing to verify its function and performance. The final system consisted of two box platforms that can individually perform vertical and angled surface perturbations. Following a perturbation, the system can automatically reset for the next iteration under the weight of the standing participant. The PPS achieves a peak downward acceleration of 4.4 m/s² during drop events that simulate sudden surface changes. The experimental testing revealed that the perturbation induced a peak limb loading of 280 ± 38 % of body weight (BW) during vertical drops and that participants' center of mass displacements were consistent with previous balance studies evaluating vertical perturbations. The system can be used in a laboratory or clinical setting to better understand balance response and control mechanisms and assist in rehabilitation training to improve balance control and help mitigate the incidence of falls.