Improving postural control by applying mechanical noise to ankle muscle tendons

Abstract

The application of subthreshold mechanical vibrations with random frequencies (white mechanical noise) to ankle muscle tendons is known to increase muscle proprioceptive information and to improve the detection of ankle movements. The aim of the present study was to analyze the effect of this mechanical noise on postural control, its possible modulation according to the sensory strategies used for postural control, and the consequences of increasing postural difficulty. The upright stance of 20 healthy young participants tested with their eyes closed was analyzed during the application of four different levels of noise and compared to that in the absence of noise (control) in three conditions: static, static on foam, and dynamic (sinusoidal translation). The quiet standing condition was conducted with the eyes open and closed to determine the subjects' visual dependency to maintain postural stability. Postural performance was assessed using posturographic and motion analysis evaluations. The results in the static condition showed that the spectral power density of body sway significantly decreased with an optimal level of noise and that the higher the spectral power density without noise, the greater the noise effect, irrespective of visual dependency. Finally, noise application was ineffective in the foam and dynamic conditions. We conclude that the application of mechanical noise to ankle muscle tendons is a means to improve quiet standing only. These results suggest that mechanical noise stimulation may be more effective in more impaired populations.

Improved proprioceptive function by application of subsensory electrical noise: Effects of aging and task-demand

“…For instance, during a sensory conflict task (i.e., moving visual surrounding), addition of mechanical noise improved postural control in older adults (Dettmer et al, 2015) but no effects were observed in young adults (Keshner et al, 2014;Dettmer et al, 2015). On the other hand, no effects of SR mechanical stimulation on postural control were obtained during translation of support surface in both young and older adults (Borel and Ribot-Ciscar, 2016;Dettmer et al, 2016). Considering that SR effects on motor control still need to be further understood, the goal of the present research was to verify if there are age-related differential SR effects when electrical noise is applied during tasks with different sensory (visual) demands.…”

Vibrotactile Feedback for Improving Standing Balance

“…Participants from group 2 performed also the sham test, i.e., they were asked to stand still for three additional 50 s trials where the first and the last trial were without any feedback (V − T − ; T9-T11), and the second trial with the sham feedback (V − T +S ; T10), i.e., a vibrotactile feedback where the vibration intensity was not related to the actual CoM oscillations (see Vibrotactile Feedback Control section). The rationale of testing the effect of sham feedback was to verify if measurable sway changes observed in our experiment were due (1) to the informational content of the supplemental vibrotactile feedback or (2) to a mere effect of vibration acting as noise and increasing the perceptive thresholds as in Dhruv et al (2002), Liu et al (2002), Janssen et al 2010, Magalhães and Kohn (2011), Borel and Ribot-Ciscar (2016), and Kwak et al (2016). In the latter case, we expected that changesand specifically a reduction-of the postural sway during the exposure to the synchronized informative feedback, would have been maintained during the exposure to the unsynchronized sham feedback.…”

“…The lack of effect on the postural sway of the two different encodings methods described above could be due to the exposure to vibration, with different directional effects because the vibrator motors being located on the front/back of the participants, i.e., the vibration was provided along the AP direction. In fact it is well-known that also a low-level noise vibrotactile stimulation increase the detection of the stimuli, leading to improvements in postural control (Gravelle et al, 2002;Priplata et al, 2002Priplata et al, , 2003Magalhães and Kohn, 2011;Borel and Ribot-Ciscar, 2016;Kwak et al, 2016). To verify whether or not the participants in this experiment integrated their neural control of the informational content encoded in the vibration, we added a trial where the participants of group 2 where exposed to sham feedback.…”

“…To verify the effects of this sham feedback per se, we should have added a group that would have being exposed only to sham feedback (or at least exposed first to the sham feedback). Pursuing this extension of the line of research performed by the current study we should also have taken into account that the relation between the body sway and the intensity of vibratory noise has a U-like shape, thus only specific levels of noise might induce a decrease of postural performance (Magalhães and Kohn, 2011;Borel and Ribot-Ciscar, 2016;Kwak et al, 2016). However, this was not our goal, but we just wanted to verify the mechanisms underlying the changes in the postural sway due to the vibration we provided encoding the CoM information, as in Krueger et al for the upper limb supplemental feedback (Krueger et al, 2017).…”

“…For example, there is evidence that humans modify their postural sway (Goodworth et al, 2009;Loughlin et al, 2011) in presence of vibrotactile feedback, encoding velocity and/or position of the body Center of Mass (CoM) or the Center of Pressure (CoP). However, other studies have shown that also a low level of vibrational noise, e.g., mechanical or electrical, is useful to improve postural stability, enhancing the sensitivity of the somatosensory system (Dhruv et al, 2002;Liu et al, 2002;Janssen et al, 2010;Magalhães and Kohn, 2011;Borel and Ribot-Ciscar, 2016;Kwak et al, 2016). This kind of stimulation (e.g., stochastic resonance) resulted in a reduction of the postural sway in elderly people (Gravelle et al, 2002;Priplata et al, 2002Priplata et al, , 2003 and in people affected by vestibular impairments (Janssen et al, 2010).…”