Dynamic postural control during (in)visible curb descent at fast versus comfortable walking velocity

BACKGROUND

The unexpectedness of ground-contact onset in stepping down due, e.g., to a camouflaged curb during ongoing gait may impose potential postural control challenges, which might be deteriorated when walking faster.

RESEARCH QUESTION

Does traversing camouflaged versus visible curbs, at a fast walking velocity, induce more unstable body configurations, assessed by a smaller anteroposterior "margin of stability" (MoS)?

METHODS

For twelve healthy participants, we investigated MoS at foot touchdown in descent and in the first recovery step from 0- and 10-cm visible and camouflaged curbs at comfortable (1.22 ± 0.08 m/s) and fast (1.71 ± 0.11 m/s) walking velocities. Three-way (velocity, elevation, visibility) and two-way (velocity, visibility) repeated-measurement ANOVAs were performed to determine their interactions on MoS, and its determining parameters, during curb negotiation and recovery step, respectively.

RESULTS

No greater postural instability when traversing a camouflaged versus visible curb at a faster walking velocity during curb descent, indicated by no three-way interaction effects on MoS. However, an elevation-by-visibility interaction showed a dramatic decrease of MoS when descending a 10-cm camouflaged versus visible curb. This was because of a farther anterior displacement of center-of-mass with a larger velocity. Furthermore, the walking velocity was independently associated with a smaller MoS and a more anteriorly-shifted center-of-mass with a higher velocity. In the recovery step, participants demonstrated a reduced stability of the body configuration when walking faster or recovering from a camouflaged than from a visible curb. The mentioned result implies that the potential to increase the base-of-support to compensate for an increased center-of-mass velocity, induced by an increased walking velocity, is limited.

SIGNIFICANCE

Despite a significant independent main effect of walking velocity, a more unstable postural control observed during traversing of camouflaged versus visible curbs was found not to be walking velocity-related in young individuals. Further research, including elderly may shed more light on these results.

The effects of an expected twofold perturbation on able-bodied gait: Trunk flexion and uneven ground surface

BACKGROUND

Although alteration in trunk orientation and ground level potentially affects gait pattern individually, it is plausible to examine the interaction effects of such factors.

OBJECTIVE

The interaction effects between trunk-flexed gait and uneven ground on able-bodied gait pattern.

METHODS

For twelve able-bodied participants, we compared the adaptive mechanisms in kinematics, kinetics and spatial-temporal parameters of gait (STPG) with bent postures (30° and 50° of sagittal trunk flexion) across uneven surface (10-cm visible drop at the sight of the second ground contact) with that of upright posture on even ground surface.

RESULTS

Significant between-posture changes on the uneven surface included a decreased peak ankle dorsiflexion angle and vertical ground reaction force (GRF) 2nd peak as trunk flexion increased. Moreover, significant between-ground surface changes for each individual gait posture were a decreased peak ankle dorsiflexion angle and ankle range of motion irrespective of trunk posture and a reduced trailing step duration and vertical GRF 2nd peak in upright walking. The spatial parameters of gait remained unchanged across uneven surface, but at the expense of pronounced adjustments in temporal parameters, i.e., a more conservative gait strategy, indicating a distinct contribution from spatial and temporal strategies in trunk-flexed gaits. This was associated with greater peak flexion angles across lower limb joints regardless of trunk posture, alongside with an exertion of greater forces at faster rates earlier in stance and attenuated forces at lower rates at the end of the stance (i.e., early-skewed vertical GRF). When considering the main effect of posture, a more crouched gait was executed with reduced temporal parameters (except for cadence) and an early-skewed vertical GRF patterns with increasing trunk flexion.

SIGNIFICANCE

These results may have implications for understanding the nature of compensatory mechanisms in gait pattern of older adults and/or patients with altered trunk orientations while accommodating uneven ground.