Ankle Torque During MidStance Does Not Lower Energy Requirements of Steady Gaits In this paper, we investigate whether applying ankle torques during midstance can be a more effective way to reduce energetic cost of locomotion than actuating leg length alone. Ankles are useful in human gaits for many reasons including static balancing. In this work, we specifically avoid the heelstrike and toeoff benefits to investigate whether the progression of the center of pressure from heeltotoe during midstance, or some other approach, is beneficial in and of itself. We use an Ankle Actuated Spring Loaded Inverted Pendulum model to simulate the shifting center of pressure dynamics, and trajectory optimization is applied to find limit cycles that minimize cost of transport. The results show that, for the vast majority of gaits, ankle torques do not affect cost of transport. Ankles reduce the cost of transport during a narrow band of gaits at the transition from grounded running to aerial running. This suggests that applying ankle torque during midstance of a steady gait is not a directly beneficial strategy, but is most likely a path between beneficial heelstrikes and toeoffs.

TIP Model: A Combination of Unstable Subsystems for Lateral Balance in Walking Balancing or postural stability is one of important locomotor subfunctions in bipedal gaits. The inverted pendulum and virtual pivot point (VPP) are common modeling approaches to analyze balance control in human and robot walking. In this paper, we employ the VPP concept to investigate posture control in the frontal plane. The outcomes demonstrate that unlike posture control in the sagittal plane, the VPP in the frontal plane is place below center of mass. This finding explains a novel hybrid strategy for lateral stability in human walking. The here proposed model shows that switching between unstable inverted virtual pendulums generate stable posture control in the frontal plane. This outcome is consistent within a group of seven human subjects walking at normal and slow speeds.