Vestibular contributions to balance control during stair negotiation versus walking and changes with aging.

Falls on stairs become more likely with age, partly due to deterioration of the sensorimotor systems essential to balance. The vestibular system, critical for balance control, experiences significant deterioration losing up to 40% of its motion-sensing hair cells by age 70. Signal transmittance also appears to increasingly act like a low-pass filter with age, due to several potential mechanisms. This study aimed to explore the vestibular contributions to balance control during stair negotiation to determine if aging increases reliance on low-frequency vestibular signals similar to standing during dynamic tasks. We hypothesized that older adults would exhibit greater low-frequency vestibular stimulus correlated responses than younger adults during walking and stair negotiation. Fifteen young and fifteen older adults performed stair ascent and stair descent, and treadmill walking while receiving electric vestibular stimulation. Vestibular stimulus correlated responses were quantified by measuring coherence and gain between a 0-25 Hz random waveform electric vestibular stimulus electromyographic activity in seven hip and leg muscles. We found older adults generally exhibited greater 'low' frequency (0-10 Hz) coherence relative to younger adults, whereas, younger adults exhibited greater coherence at higher frequencies (10-25 Hz). These findings not only provide evidence in support our hypothesis but also invite a broad discussion of alternative interpretations that may underlie the age-related shift in how different frequency vestibular signals influence muscle activity during dynamic balance tasks. More broadly, this study enhances our understanding of how aging affects thevestibular cues used during stair negotiation and walking.