Analysis of dynamics properties of ankle joint during push-forward disturbance rejection

Ankle joint dynamics properties have been widely studied because of their important role in interaction with environment. In this paper, these properties were studied under the experimental condition of push-recovery. The disturbance was exerted on backs of subjects. The amplitude of disturbance was limited so that only ankle joint strategy was evoked, without foot tilting. A data-synchronized-collection system was developed to measure ankle joint kinematics, kinetics and sEMG information. Ankle joint mechanical impedance, i.e. torque adjustment corresponding to joint angle, was investigated together with sEMG of antagonistic and agonistic muscles. Despite of complication of muscle-skeleton structure and central nervous system, a simple control mechanism was observed, describing by linear and quadratic polynomials with high correlation coefficient. Experimental results also indicated that the reflex-like behavior takes charge with the resistant torque generation at the first moment, helping to adjust ankle joint mechanical impedance. Furthermore, SOL muscle activation level had a linear relationship with ankle joint kinematics data. This pilot study is as one part of our investigation of human push-recovery ability, which tries to reveal the mechanism of ankle dynamics and helps to improve bipedal robot balance capability.