title: The altered vestibular-evoked myogenic and whole-body postural responses in old men during standing.
abstract: Age-related decrements within the sensorimotor system may lead to alterations and impairments in postural control, but a link to a vestibular mechanism is unclear. The purpose of the present study was to determine whether vestibular control of standing balance is altered with adult aging. Eight old (~77 years) and eight young (~26 years) men stood without aids on a commercially available force plate with their head turned to the right, arms relaxed at their sides and eyes closed while receiving stochastic vestibular stimuli (0-25 Hz, root mean square amplitude=0.85 mA). Surface electromyography signals were sampled from the left soleus, medial gastrocnemius and tibialis anterior. Whole-body balance, as measured by the anteroposterior forces and muscle responses, was quantified using frequency (coherence and gain functions) and time (cumulant density function) domain correlations with the vestibular stimuli. Old men exhibited a compressed frequency response of the vestibular reflex with a greater relative gain at lower frequencies for the plantar flexors and anteroposterior forces than young. In the time domain, the peak amplitude of the short latency response was 45-64% lower for the plantar flexors and anteroposterior forces (p≤0.05) in the old than young, but not for the tibialis anterior (p=0.21). The old men had a 190% and 31% larger medium latency response for only the tibialis anterior and anteroposterior forces, respectively, than young (p≤0.01). A strong correlation between the tibialis anterior and the force response was also detected (r=0.80, p<0.01). In conclusion, net vestibular-evoked muscle responses led to smaller short and larger medium latency peak amplitudes in anteroposterior forces for the old. The present results likely resulted from a compressed and lower operational frequency range of the vestibular reflexes and the activation of additional muscles (tibialis anterior) to maintain standing balance.
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada; Department of Human Physiology, University of Oregon, Eugene, OR, United States.
authors.forename: Brian H
authors.initials: BH
authors.lastname: Dalton
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada; Brain Research Center, University of British Columbia, Vancouver, British Columbia, Canada; Institute for Computing, Information and Cognitive Systems, University of British Columbia, Vancouver, British Columbia, Canada. Electronic address: jsblouin@mail.ubc.ca.
authors.forename: Jean-Sébastien
authors.initials: JS
authors.lastname: Blouin
authors.affiliation: Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada.
authors.forename: Matti D
authors.initials: MD
authors.lastname: Allen
authors.affiliation: Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada; Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Rice
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada; Brain Research Center, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: J Timothy
authors.initials: JT
authors.lastname: Inglis
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D012018:Reflex / Q000502:physiology; D013269:Stochastic Processes; D014722:Vestibule, Labyrinth / Q000502:physiology*; D055815:Young Adult
keywords: Aging; Electromyography; Galvanic vestibular stimulation; Sensorimotor; Standing balance