Human balance as a resonance-governed system: targeted modal attenuation via passive mass coupling

Human postural control during quiet standing has often been modelled as a lightly damped dynamical system in which low-frequency modes contribute to sway behaviour. Reduced effective damping may increase amplification of these modes, potentially contributing to instability. In engineered systems, resonance amplification is commonly mitigated through frequency-selective energy redistribution using tuned mass dampers, raising the question of whether analogous principles apply to biological control systems. Here, we develop a theoretical framework linking classical vibration absorption to a reduced-order model of human postural dynamics, showing how passive mass coupling reshapes the frequency response of the system. The virtual tuned mass damper reduced compliance near the dominant low-frequency mode without globally suppressing motion. For moderate intrinsic damping (ζh = 0.15), peak response amplitude was reduced by approximately 20%. Effectiveness increased as intrinsic damping decreased, with optimized peak compliance reductions of 52% at ζh = 0.05 compared with 12% at ζh = 0.25. Compliance landscapes exhibited a well-defined optimal basin, indicating robust parameter selection. Sensitivity analyses revealed a nonlinear relationship between intrinsic damping and attenuation effectiveness. Together, these findings demonstrate that passive mass coupling can selectively redistribute low-frequency sway energy within a simplified balance model and provide a mechanistic basis for investigating resonance-targeted approaches to wearable balance assistance.