Abstract
Various diseases are associated with the impaired control of the medio-lateral (ML) position of the centre of feet pressure (CoP), and several manoeuvres have been proposed for enhancing the CoP symmetry. Here, we assessed in healthy standing subjects the feasibility and outcome of a novel protocol entailing a reaction to a continuous asymmetric ML displacement (10 cm) of the support base. The periodic perturbation consisted of a fast half-cycle (0.5 Hz) followed by a slow half-cycle (0.18 Hz). One hundred successive horizontal translation cycles were delivered in sequence. Eyes were open or closed. CoP was recorded before, after, and during the stimulation by a dynamometric platform fixed onto the translating platform. We found that the post-stimulation CoP was displaced towards the direction of the fast half-cycles. The displacement lasted several tens of seconds. Vision did not affect the amplitude or duration of the post-stimulation effect. The magnitude of post-stimulation CoP displacement was related to the perturbation-induced ML motion of CoP recorded during the stimulation. Over the successive perturbation cycles, the time-course of this motion revealed an adaptation phenomenon. Vision moderately reduced the adaptation rate. The findings support the feasibility of the administration of a simple asymmetric balance perturbation protocol in clinical settings to help patients recover the symmetry of the CoP. This protocol needs to be further validated in older populations and in patients.
Highlights
Numerous studies on the control of quiet stance have focused on balance and balance control in the anterior–posterior (AP) plane [1,2], likely because of the analogy of the body profile in the sagittal plane with an inverted pendulum that facilitates a formal treatment of AP sway [3]
The centre of feet pressure (CoP) was recorded by the force platform firmly mounted onto the motorized platform translating in the frontal plane with two asymmetric cycle profiles
The red area in panel B indicates the medio-lateral shift to the right direction of the ML CoP post-stimulation with respect to its pre-stimulation mean position
Summary
Numerous studies on the control of quiet stance have focused on balance and balance control in the anterior–posterior (AP) plane [1,2], likely because of the analogy of the body profile in the sagittal plane with an inverted pendulum that facilitates a formal treatment of AP sway [3]. The weight of the body is symmetrically distributed, so that the centre of feet pressure (CoP) remains halfway the distance between the feet [6]. This is at variance with the position of the CoP in the sagittal plane, where it lies ahead of the ankle joint, requiring the tonic activity of the foot, leg and axial postural muscles to avoid falling forwards [7,8]. Distinctive control modes and muscle activities appear to regulate body sway in the frontal compared to the sagittal plane [6,9,10,11,12]
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