The Vestibular Control of Balance is an Imbalance of Dorsiflexion and Plantar Flexion in Older Females

By Phuong Lisa Ha & Mathew Debenham,

Standing balance is important for tasks of daily living, and involves the complex integration of sensorimotor signals within the central nervous system. With aging, standing balance performance declines alongside strength and power. Age-related decrements within the vestibular system (e.g., impairment in vestibular hair cell receptors) could lead to a failure in properly detecting head motion and further impair postural control. There is some evidence that in response to age-related decline in the peripheral vestibular system function, the central nervous system increases its sensitivity to enhance vestibular-driven reflexes for gaze stabilization and maintaining balance. Additionally, following fatiguing ankle flexor exercise, young males appear to have increased vestibular-evoked balance responses, which may be a compensatory strategy for the reduced strength of the ankle muscles. Yet, it is unclear if age-related muscle weakness also increases the sensitivity of the vestibular control of balance, similarly to exercise-induced muscle weakness.

To answer this question, we evaluated knee extensor muscle strength and power in eight young (20-24 years old) and eight older females (63-76 years old). On a separate visit, we assessed their balance in response to vestibular stimulation; we applied a small electrical current on the mastoid processes (just behind the ear) while participants stood quietly on a force plate for two, 90-s trials. We recorded anterior-posterior ground reaction forces and muscle activity of the dorsi- and plantar flexors.

Figure: Assessment protocol; left: lower limb strength testing; right: quiet standing trials under vestibular stimulation.

We found that compared to their younger counterparts, older females had weaker and less powerful knee extensor muscles. They also exhibited larger vestibular-evoked balance responses, which were associated with increased muscle activity in the dorsiflexors, but not plantar flexors. The vestibular-evoked balance response was also significantly correlated with maximal knee extensor power.

In conclusion, we suggest that the larger vestibular-evoked balance responses in older females may be linked to a compensatory strategy that uses greater activation of the dorsiflexors to stabilize, at least, in part, for age-related reductions in knee extensor power.

Publication

Ha, P. L., Peters, W. B., McGeehan, M. A., & Dalton, B. H. (2022). Age-related reduction in peak power and increased postural displacement variability are related to enhanced vestibular-evoked balance responses in females. Experimental gerontology, 111670. https://doi.org/10.1016/j.exger.2021.111670

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