Abstract
Though the effects of imposed trunk posture on human walking have been studied, less is known about such locomotion while accommodating changes in ground level. For twelve able participants, we analyzed kinematic parameters mainly at touchdown and toe-off in walking across a 10-cm visible drop in ground level (level step, pre-perturbation step, step-down, step-up) with three postures (regular erect, ~30° and ~50° of trunk flexion from the vertical). Two-way repeated measures ANOVAs revealed step-specific effects of posture on the kinematic behavior of gait mostly at toe-off of the pre-perturbation step and the step-down as well as at touchdown of the step-up. In preparation to step-down, with increasing trunk flexion the discrepancy in hip−center of pressure distance, i.e. effective leg length, (shorter at toe-off versus touchdown), compared with level steps increased largely due to a greater knee flexion at toe-off. Participants rotated their trunk backwards during step-down (2- to 3-fold backwards rotation compared with level steps regardless of trunk posture) likely to control the angular momentum of their whole body. The more pronounced trunk backwards rotation in trunk-flexed walking contributed to the observed elevated center of mass (CoM) trajectories during the step-down which may have facilitated drop negotiation. Able-bodied individuals were found to recover almost all assessed kinematic parameters comprising the vertical position of the CoM, effective leg length and angle as well as hip, knee and ankle joint angles at the end of the step-up, suggesting an adaptive capacity and hence a robustness of human walking with respect to imposed trunk orientations. Our findings may provide clinicians with insight into a kinematic interaction between posture and locomotion in uneven ground. Moreover, a backward rotation of the trunk for negotiating step-down may be incorporated into exercise-based interventions to enhance gait stability in individuals who exhibit trunk-flexed postures during walking.
Highlights
In a recent study [37] focusing on kinetic adjustments in walking across uneven ground, we found reduced between-step variations in the ground reaction force (GRF) patterns with increasing trunk flexion
Considering an altered dynamics of the trunk-flexed gaits from regular upright walking [5,6,7, 18, 27, 28, 31], the context-specific kinetic and kinematic adaptations during walking and the intra-limb kinetic and kinematic asymmetries in leg function at TD and TO as a result of an increased sagittal trunk flexion [5], this study aims at examining the adaptive locomotor kinematic behavior in perturbed steps (10 cm visible drop; level step, pre-perturbation step, step-down, step-up) while walking with three postures
The backward rotation in regular erect trunk alignment (RE) gait increased from 3.5 ± 0.8 ̊ during level walking to 5.7 ± 1.9 ̊ during step-down
Summary
In addition to investigating a locomotor system operating in steady-state conditions, the study of its behavior when coping with perturbations can lead to further identification of the system. Human must ensure a forward progression in accordance with dynamic equilibrium, but is required to continuously cope with perturbations—such as postural changes, terrain variations, obstacles, drops, etc.—in an anticipatory fashion through coordinated interactions between different body segments [2, 3]. Maintaining dynamic stability across uneven ground can be a critical issue to locomotion. Imposed trunk flexion [5,6,7] and changing ground level [8, 9] have been proposed as two types of perturbations to human locomotion
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