Understanding the Role of Time-Delay on Maintaining Upright Stance on Rotational Balance Boards

Mathematical models of human posture on a rigid surface predict two types of balance instabilities — a static tipping instability and a dynamic instability leading to large oscillations. Although a common technique to improve balance performance is placing patients on balance boards, little research has modeled bipedal posture on rotational boards to better understand the mechanisms underlying improvement. In this study we present a mathematical model of human stance on a single-degree-of-freedom balance board with controllable torsional stiffness and delayed feedback. Through a bifurcation analysis we find that the standard manipulation of decreasing board stiffness can lead to very different instabilities depending on an individual’s neuromuscular time-delay. This dependency limits the ability to use traditional boards for training and identification of balance deficits. We show that implementing a controllable time-delay may be more beneficial and allow for the customization of treatment plans for individual with very different characteristics.