The Effect of the Balance Board Mass on the Stability, Equilibrium, and Robustness of the Human-Balance Board System

People with neuromuscular deficits may show balance issues that put them in a higher risk of fall as compared to healthy people. To reduce the risk of fall, balance-board (BB)-based rehabilitation intervention has been widely used. However, despite the extensive use of BB- based interventions, the mechanisms responsible for rehabilitation remain unclear. To better understand these mechanisms, several studies have used a system dynamics approach to investigate the effect of neuromuscular deficits (visual, vestibular, proprioceptive) and sensorimotor latencies on the stability and dynamical behavior of the human-BB system. Though, to the best knowledge of the authors, the effect of the BB mass on the stability and dynamics of the human-BB system has never been investigated. In the present study, bifurcation analyses, root finding techniques, and computational simulations are used to investigate the effect of the BB mass and BB time-delay on the stability, equilibrium, and robustness of the human-BB upright posture (UP) for cases where either proprioceptive or visual and vestibular deficits are considered. The results show that the BB mass and BB time-delay play a critical role on the UP stability, leaning postures, and robustness of the human-BB system. In fact, increasing BB mass reduces the range of neuromuscular gains that stabilize the system and shrinks the basin of attraction of the UP, which is related to the human-BB system's robustness to posture disturbances. This effect is more evident in the case where visual and vestibular deficits are considered in simulation. This relationship may have implications on the design and development of BBs with tunable mass and tunable time-delay. The BB could be designed to tune time-delay and mass, so patients could be better challenged during BB-based intervention in a more patient-specific manner.