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 degrees and 50 degrees 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.