Locomotor stability in able-bodied trunk-flexed gait across uneven ground

Abstract This study aimed to explore the control of dynamic stability of the imposed trunk-flexed gaits across uneven ground. For ten young healthy participants, we compared the anteroposterior margin of stability (MoS) and lower limb joint kinematics at foot-contact during accommodating a consecutive stepdown and step-up (10-cm visible drop) to that of level steps while maintaining four postures: regular erect, ∼30°, ∼50° and maximal trunk flexion from the vertical. Two-way repeated measures ANOVAs revealed no significant step × posture interactions for the MoS ( p  = .187) and for the parameters that contributed to the MoS calculation ( p  > .05), whereas significant interactions were found for the hip flexion, hip position (relative to the posterior boundary of the base of support) and the knee flexion. The main effect of step ( p  = .0001), but not posture ( p  = .061), on the MoS was significant. Post hoc tests, compared with the level step, showed that the decreased magnitude of the MoS during stepping down ( p  = .011)—mainly due to a further forward displacement of the center of mass position ( p  = .006)—significantly increased in the immediate following step-up ( p  = .002) as a consequence of a substantial increase in the base of support ( p  = .003). In the stepdown versus level step, the hip and knee flexions as well as the hip position did not significantly change in the trunk-flexed gaits ( p  > .05). In the step-up, the knee flexion increased (except for the gaits with the maximum trunk flexion), whereas other kinematic variables remained unchanged. Quantifying the step-to-step control of dynamic stability in a perturbed walking reflected continuous control adaptations through the interaction between gait and posture. In fact, the able-bodied participants were able to safely control the motion of the body’s CoM with the combination of compensatory kinematic adjustments in lower-limb and adaptations in stepping pattern.