Stabilization of an unstable equilibrium of a balance platform due to short-term training

We study experimentally and numerically the dynamics of a balance platform during a short-term training. The results of experiments with sixteen untrained subjects and a developed empirical biomechanical model exhibit the coexistence of three attractors under adaptive control of multistability. During the experiments, we measure the balance bar angle, angular velocity, and angular acceleration. Simultaneously, superficial electromyography (EMG) is recorded on the flexors and extensors of the ankle and knee joints. Phase-space analysis of the platform movement shows that the time the platform spends near the unstable equilibrium correlates with the average muscle activity. We also observe that the balance platform dynamics differs when the subject starts balancing with his/her dominant or non-dominant leg. In addition, we find that subjects with better symmetry between the strength of dominant and non-dominant legs demonstrate higher training efficiency. Therefore, the balance control efficiency can be enhanced by training muscles of the non-dominant leg. The results of numerical simulations are in good agreement with experiments. •An empirical double-well potential model is developed to describe balance platform dynamics during balance experiments.•Short-term training improves stability of a third coexisting attractor created from an unstable equilibrium.•More correlated muscle interaction in the nondominant leg is required to maintain balance more efficiently.