How attentional focus on body sway affects postural control during quiet standing

Abstract

The purpose of this study was to investigate how attentional focus on body sway affects postural control during quiet standing. To address this issue, sixteen young healthy adults were asked to stand upright as immobile as possible on a force platform in both Control and Attention conditions. In the latter condition, participants were instructed to deliberately focus their attention on their body sways and to increase their active intervention into postural control. The critical analysis was focused on elementary motions computed from the centre of pressure (CoP) trajectories: (1) the vertical projection of the centre of gravity (CoG(v)) and (2) the difference between CoP and CoG(v) (CoP-CoG(v)). The former is recognised as an index of performance in this postural task, whilst the latter constitutes a fair expression of the ankle joint stiffness and is linked to the level of neuromuscular activity of the lower limb muscles required for controlling posture. A frequency-domain analysis showed increased amplitudes and frequencies of CoP-CoG(v) motions in the Attention relative to the Control condition, whereas non-significant changes were observed for the CoG(v) motions. Altogether, the present findings suggest that attentional focus on body sway, induced by the instructions, promoted the use of less automatic control process and hampered the efficiency for controlling posture during quiet standing.

Effects of attentional focus on postural sway in children and adults

“…This confirmed in children as in adults that postural stability decreases when attention is focused on postural sway, which may be explained by an increase of the neuromuscular activity (Vuillerme and Nafati 2007;Wulf and Prinz 2001;Zachry et al 2005). At least since the age of 4, focusing attention on the control of upright stance would increase the number of motor units recruited in the lower limb muscles that are involved.…”

“…Nevertheless, some recent investigations provided evidence that the regulation of posture, from the simplest task (i.e., orthostatic) to the most complex one (i.e., unipodal balance), also involves attentional processes (Woollacott and Shumway-Cook 2002;Vuillerme and Nougier 2004). The mobilization of these attentional resources depends on (1) the age (Teasdale and Simoneau 2001;Woollacott and Shumway-Cook 2002), (2) the available sensory information (Shumway-Cook and Woollacott 2000; Teasdale and Simoneau 2001), (3) the postural task complexity (Lajoie et al 1996), (4) the expertise (Vuillerme and Nougier 2004), and (5) the voluntary attentional focus on body sway (Vuillerme and Nafati 2007). Indeed, these last authors observed a degradation of postural stability when it was asked to adult subjects to focus their attention on their posture.…”

“…One explanation of this degradation was that focusing attention on the movement implies an increase of the voluntary control which then comes to interfere with the automatic processes usually used to realize it (Wulf and Prinz 2001). From a neurological point of view, the degradation observed when voluntary attention focused on the movement (Zachry et al 2005) or on body sway (Vuillerme and Nafati 2007) was associated with an increase of the neuromuscular activity. These last authors interpreted this modulation of neuromuscular activity by the fact that voluntary motor control increases the recruitment of additional motor units, inducing an increase of the muscular force which in turn degrades the control of upright stance.…”

Letter to the Editor: On “Advantages and disadvantages of stiffness instructions when studying postural control” by C.T. Bonnet: Taking a step towards a broader perspective on quiet standing instructions

“…[2,3]). Experiments that manipulate instruction are widely available in the postural control literature, such as studies on internal vs. external foci of attention [26][27][28]. Researchers should of course explain the rationale behind their instructions as IDV in their papers, and as well specify the employed instructions.…”

About the structure of posturography: Sampling duration, parametrization, focus of attention (part I)

“…The reason could be the lack of adequate standardization: e.g. the sampling duration, the measurement parameters [7], focus of attention (compare part II) [8][9][10]. First, measurement durations in research typically range from several seconds (e.g.…”