Research on 3D predictive gait simulation remains limited. This study therefore verifies an existing 3D predictive gait simulation framework implemented in SCONE, with the goal that this verified framework can serve as a physiologically plausible modelling and optimisation platform for future related studies. Four optimisation criteria were selected, namely minimising cost of transport, minimising muscle activity, maxmising head instability, and minimising foot-ground impact. These criteria were combined to form a set of objective functions, under which the framework was optimised. The predicted results produced by each objective function were quantitatively compared with experimental data using Pearson r and RMSE/SD, and agreement was evaluated across multiple biomechanical categories, including joint kinematics, ground reaction forces, joint moments and joint powers. The results indicate that, under the optimal objective function, the predictive performance approaches that of the ExpTrack solution that directly tracks experimental data. The framework reproduces sagittal plane hip, knee and ankle angles, vertical and anterior-posterior ground reaction forces, all joint moments and ankle power with strong agreement, but agreement is weaker for hip adduction, medio-lateral ground reaction force, and knee and hip power. Overall, these findings demonstrate the strengths of the framework in reproducing experimental 3D gait, while also revealing limitations in medio-lateral stability control and in the current model and controller settings, providing a basis for targeted improvements in future work.

Background: Anterior cruciate ligament (ACL) injuries commonly reduce knee stability and increase joint loading, often leading to compensatory gait alterations that may increase injury risk. Functional electrical stimulation (FES) of the biceps femoris long head (BFLH) during the gait stance may improve knee stability by reducing harmful joint loading, but the effects on voluntary muscle control remain unclear.

Research question: This study examined whether FES of the BFLH during the stance phase of the gait reduces ACL-relevant knee joint loading in healthy adults and whether it alters voluntary muscle control. Additionally, the use of gluteus maximus (GLMAX) sEMG as a proxy for BFLH activation was assessed.

Method: Nine healthy participants walked on a treadmill under control and FES-assisted conditions. Kinematic, kinetic, and sEMG data were analyzed using statistical parametric mapping and linear mixed-effects models.

Results: FES of the BFLH significantly reduced internal knee rotation moment (KRM) with 9.37% during 42–48% of the gait cycle (p = 0.0002; d = 0.42). Knee adduction moment (KAM) showed non-significant reductions in both legs (non-stimulated: p = 0.0317, d = 0.18; stimulated: p = 0.0492, d = 0.37). Knee abduction angle (KAA) and knee rotation angle (KRA) showed no significant changes (p > 0.05). In sEMG analysis, inconsistent timing between GLMAX and BFLH activation indicated GLMAX is not a reliable surrogate for estimating BFLH activity. Regarding voluntary control, only peak KAM increased slightly over strides during FES-assisted walking (p = 0.006), possibly due to muscle fatigue. No significant retention or after-effects were observed.

Conclusion: Targeted FES of the BFLH can reduce ACL-relevant knee loading without impairing voluntary motor control. sEMG results highlight the need for direct BFLH monitoring, as GLMAX is an unreliable proxy. These findings support further exploration of FES strategies for ACL injury prevention and rehabilitation.

The metabolic cost of walking reflects gait efficiency and is influenced by biomechanical factors as walking speed. While most walking research uses treadmills, older adults are found to exhibit a greater elevation in the cost of walking on the treadmill compared to overground walking than younger adults. A possible cause for this elevation could be the higher stability demands in older adults during treadmill walking, possibly influenced by a higher vestibular contribution. This study investigated whether increased vestibular demands for balance control contribute to this elevated cost in older adults. Ten younger (mean age 26.4 years) and ten older adults (mean age 68.6 years) completed 5-minute treadmill and overground walking trials at preferred and slow fixed speeds. Metabolic cost was measured, and vestibular contributions to balance were assessed via electrical vestibular stimulation, which induced virtual movements and evoked balance correcting responses measured by inertial sensors on the back and ankles. Treadmill walking increased the cost of walking significantly by 15-23% compared to overground walking, with no significant age effect. Vestibular stimulation increased metabolic cost significantly in both overground and treadmill walking and age groups. Assessment of the vestibular contributions to kinematic measures revealed a significant increase in vestibular contribution to balance at slower walking speeds, but no significant effect of age and no large effect of treadmill or overground. Indicating that the measured participants cannot conclude that the elevation of cost in treadmill walking in older adults is due to the vestibular contribution to balance.