Centre of pressure versus centre of mass stabilization strategies: the tightrope balancing case

Abstract

This study proposes a generalization of the ankle and hip postural strategies to be applied to the large class of skills that share the same basic challenge of defeating the destabilizing effect of gravity on the basis of the same neuromotor control organization, adapted and specialized to a variable number of degrees of freedom, different body parts, different muscles and different sensory feedback channels. In all the cases, we can identify two crucial elements (the CoP, centre of pressure and the CoM, centre of mass) and the central point of the paper is that most balancing skills can be framed in the CoP–CoM interplay and can be modelled as a combination/alternation of two basic stabilization strategies: the standard well-investigated COPS (or CoP stabilization strategy, the default option), where the CoM is the controlled variable and the CoP is the control variable, and the less investigated COMS (or CoM stabilization strategy), where CoP and CoM must exchange their role because the range of motion of the CoP is strongly constrained by environmental conditions. The paper focuses on the tightrope balancing skill where sway control in the sagittal plane is modelled in terms of the COPS while the more challenging sway in the coronal plane is modelled in terms of the COMS, with the support of a suitable balance pole. Both stabilization strategies are implemented as state-space intermittent, delayed feedback controllers, independent of each other. Extensive simulations support the degree of plausibility, generality and robustness of the proposed approach.

Specific Posture-Stabilising Effects of Vision and Touch Are Revealed by Distinct Changes of Body Oscillation Frequencies

“…A light touch is a potent stabilising stimulus, able to replace vision in subjects with impaired vestibular system ( 132 – 134 ). In the present study, like in several others [( 7 ), see Lackner ( 47 ) for a recent review], the haptic information arose from the index fingertip lightly touching the force pad and from the muscles active in this task. In many studies, the vertical force of the fingertip on the force pad representing the earth-fixed reference was generally well-below 1 N and was considered to be inadequate for mechanical stabilisation ( 60 , 135 , 136 ).…”

“…A plethora of studies has been published on this topic, including some from our group ( 4 , 5 ). Body sway when standing upright on a solid base of support is normally almost negligible in healthy subjects, witnessing accurate and precise neural control ( 6 , 7 ) based on the internal model of gravitational and inertial forces ( 8 ) and on multiple inputs from the receptors detecting the body state. The excursions of the centre of foot pressure (CoP) of subjects standing quietly on the firm ground are approximately contained within the size of a dime, even if there is a large variability in sway across different healthy subjects ( 9 ).…”

Neuromuscular Control Modelling of Human Perturbed Posture Through Piecewise Affine Autoregressive With Exogenous Input Models

“…Indeed, many previous studies investigated balance responses to external perturbations relying on single-link inverted pendulum model, where the ankle joint is the only actuated joint for counteracting the disruption (Van Der Kooij and De Vlugt, 2007;Peterka, 2009;Davidson et al, 2010;Schut et al, 2020). In addition, this kind of model for the human upright stance constitutes the core of any balancing task, also in dynamical conditions, where a multi-link structure is often reduced to the CoP-COM relation (Chevallereau et al, 2008;Morasso, 2020).…”

Cutaneous and muscular afferents from the foot and sensory fusion processing: Physiology and pathology in neuropathies

“…Kiemel et al 32 noted that minimisation of muscle activity rather than of body sway per se is the main task of the postural control system during quiet stance. Independently of the underpinning mechanisms, 33 sway is a source of crucial information and in stance healthy individuals sway continually. Carpenter et al 34 suggested that the postural sway may be exploited to ensure that continuous dynamic inputs are provided by multiple sensory systems.…”