Postural Control during Pushing Movement with Risk of Forward Perturbation

Abstract

The purpose of this study was to investigate the effect of a forward bilateral pushing movement on postural control in a situation where known, unknown, and unpredictable perturbations may be induced. Participants stood upright and voluntarily pushed a handle with both hands. In the first task, the handle was free to be moved by the participant (perturbation; movable task) and in the second task, the handle was locked (stationary task). For each task, body displacement and observed applied force were recorded. Anticipatory postural control adjustment plays a vital role in body stability; however, in contrast to its role in maintaining stability, adjustment can generate a restricted voluntary movement because motor programming selects a postural control that gives priority to body stability over the target movement.

Stimulus Prediction and Postural Reaction: Phase-Specific Modulation of Soleus H-Reflexes Is Related to Changes in Joint Kinematics and Segmental Strategy in Perturbed Upright Stance

“…Three different protocols were used applying anterior/posterior surface translations (Figure 1A): (i) the perturbation direction was known and thus predictable, this protocol served as a control; (ii) aimed to assess perturbation-induced effects when unpredictable perturbations occurred randomly in an anterior or posterior direction and the direction of deterioration stimulus was unknown (Okai and Fujiwara, 2013; Kanekar and Aruin, 2014a,b); and (iii) we investigated the influence of the perturbation when subjects were cheated and the direction was indicated incorrectly. Protocols were executed in a random order by using sealed envelopes, though operators were not blinded.…”

“…Second, when compensating for an unpredictable stimulus, proactive postural adjustments are absent and reactive compensatory responses predominate. Studies show a gradually increased sway path (Jacobs et al, 2008; Santos et al, 2010; Kanekar and Aruin, 2014a,b), augmented magnitude, timing differences (Aimola et al, 2014), variability of the postural response (Okai and Fujiwara, 2013; Kanekar and Aruin, 2014a,b), modified sensory processing (Kourtis et al, 2008), changes in neuromuscular activation reflected by delayed neuromuscular responses (McChesney et al, 1996), and modulated spinal (Burleigh-Jacobs et al, 1997) and supraspinal contributions (Adkin et al, 2006; Jacobs et al, 2008), which are also related to an increased fall and injury incidence (Mawston et al, 2007; Gehring et al, 2014; Pater et al, 2015). Furthermore, a shift in balance strategy could be observed.…”

“…Furthermore, a shift in balance strategy could be observed. Unpredictable compared to predictable perturbations are associated with a gradual reduction in ankle strategy and concomitantly increased hip strategy (Mawston et al, 2007; Okai and Fujiwara, 2013; Mani et al, 2014).…”

“…Despite the widespread relevance of stimulus prediction in different areas of the rehabilitative medicine and geriatrics, as well as a substantial number of related articles (McChesney et al, 1996; Kourtis et al, 2008; Okai and Fujiwara, 2013; Kanekar and Aruin, 2014a,b), the underlying neuromuscular mechanisms in terms of posture control are poorly understood. No study has analyzed the interrelation of neuromuscular and kinematic modulations in terms of the three modalities of prediction.…”