title: Sub-sensory vibratory noise augments the physiologic complexity of postural control in older adults.
abstract: Postural control requires numerous inputs interacting across multiple temporospatial scales. This organization, evidenced by the "complexity" contained within standing postural sway fluctuations, enables diverse system functionality. Age-related reduction of foot-sole somatosensation reduces standing postural sway complexity and diminishes the functionality of the postural control system. Sub-sensory vibrations applied to the foot soles reduce the speed and magnitude of sway and improve mobility in older adults. We thus hypothesized that these vibration-induced improvements to the functionality of the postural control system are associated with an increase in the standing postural sway complexity.
  
  
  
  Twelve healthy older adults aged 74 ± 8 years completed three visits to test the effects of foot sole vibrations at 0 % (i.e., no vibration), 70 and 85 % of the sensory threshold. Postural sway was assessed during eyes-open and eyes-closed standing. The complexity of sway time-series was quantified using multiscale entropy. The timed up-and-go (TUG) was completed to assess mobility.
  
  
  
  When standing without vibration, participants with lower foot sole vibratory thresholds (better sensation) had greater mediolateral (ML) sway complexity (r (2) = 0.49, p < 0.001), and those with greater ML sway complexity had faster TUG times (better mobility) (r (2) = 0.38, p < 0.001). Foot sole vibrations at 70 and 85 % of sensory threshold increased ML sway complexity during eyes-open and eyes-closed standing (p < 0.0001). Importantly, these vibration-induced increases in complexity correlated with improvements in the TUG test of mobility (r (2) = 0.15 ~ 0.42, p < 0.001 ~ 0.03).
  
  
  
  Sub-sensory foot sole vibrations augment the postural control system functionality and such beneficial effects are reflected in an increase in the physiologic complexity of standing postural sway dynamics.
authors.affiliation: Institute for Aging Research, Hebrew SeniorLife, Roslindale, MA, USA. JunhongZhou@hsl.harvard.edu.|Beth Israel Deaconess Medical Center, Boston, MA, 02131, USA. JunhongZhou@hsl.harvard.edu.|Harvard Medical School, 1200 Centre Street, Boston, MA, 02131, USA. JunhongZhou@hsl.harvard.edu.
authors.forename: Junhong
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Institute for Aging Research, Hebrew SeniorLife, Roslindale, MA, USA.|Beth Israel Deaconess Medical Center, Boston, MA, 02131, USA.|Harvard Medical School, 1200 Centre Street, Boston, MA, 02131, USA.
authors.forename: Lewis
authors.initials: L
authors.lastname: Lipsitz
authors.affiliation: Institute for Aging Research, Hebrew SeniorLife, Roslindale, MA, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Habtemariam
authors.affiliation: Institute for Aging Research, Hebrew SeniorLife, Roslindale, MA, USA.|Beth Israel Deaconess Medical Center, Boston, MA, 02131, USA.|Harvard Medical School, 1200 Centre Street, Boston, MA, 02131, USA.
authors.forename: Brad
authors.initials: B
authors.lastname: Manor
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019277:Entropy; D005260:Female; D005528:Foot; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D009622:Noise; D004856:Postural Balance / Q000502:physiology*; D012684:Sensory Thresholds; D014732:Vibration; D014785:Vision, Ocular
keywords: Multiscale entropy; Postural sway; Somatosensation; Stochastic resonance; Vibration