Neuromechanical Control Strategies of Frontal-Plane Angular Momentum of Human Upper Body during Locomotor Transitions

Control of whole-body angular momentum (H) is important for robots and humans alike to maintain dynamic balance during locomotion. H is directly related to body dynamics through external moments and ground reaction forces. The human upper body is a critical contributor to H, and deficient control of the trunk has been related to poor dynamic balance. We examined the neuromechanical control strategies of frontal plane angular momentum of trunk (Ht) during locomotor transitions while walking overground. Five healthy subjects completed ten types of transitions of altered anticipation (anticipated, unanticipated), complexity (straight walking, cuts, cut-stair ascent), and cutting style (crossover, sidestep). The average positive and negative frontal plane Ht were significantly larger in unanticipated transitions, in which crossover cut-stairs were 144^% higher in positive Ht and sidestep cut-stairs were 147^% higher in negative Ht than normal walking. Furthermore, during anticipated states, crossovers had different magnitudes of average Ht relative to sidesteps, indicating a preparatory control of the magnitude of Ht based on cutting style, not complexity. The timing of Ht lagged during unanticipated transitions relative to anticipated transitions except for cut-stairs tasks. In addition, the timing of Ht in unanticipated states was not different from anticipated states at the end of transition, indicating an adapting control pattern of timing throughout the course of the entire unanticipated transitions. These results suggest that individuals may face more challenges in controlling trunk dynamic balance during anticipated and unanticipated transitions, and represent an opportunity for emerging robotic assistive devices that target upper-body mechanics during locomotion.