Effects of Balance Training on Corticospinal Excitability in People With Chronic Ankle Instability

Plain-language summary

Ankle sprains are prevalent and debilitating injuries in daily living and sports activities. The emergency room annually cares for over 206,000 patients with lateral ankle sprain in the United States, resulting in over $12,000 of health care cost per injury. Although many rehabilitation techniques for ankle sprains have been implemented, up to 40% of individuals with ankle sprains experience residual symptoms including recurrent sprain, episodes of ankle joint "giving way," and feelings of instability, which collectively define chronic ankle instability (CAI). Individuals with CAI commonly exhibit neuromuscular dysfunction with reduced motor control due to decreased sensory input to the central nervous system (CNS) after the initial injury. As a result, the CNS sends altered motor signals to lower extremity muscles. These CNS changes contribute to various neuromuscular impairments in CAI patients, the most common of which is reduced balance performance. Neural stimulation techniques, such as the Hoffman reflex (H-reflex) and transcranial magnetic stimulation (TMS) have been used to directly assess changes in the CNS. One of the most consistently identified CNS changes in individuals with CAI is reduced ability to modulate spinal reflex excitability and corticospinal excitability of the calf muscle when transitioning from simpler to more complex balance conditions. Neural excitability refers to the ability of the central nervous system to elicit skeletal muscle contractions. That is, the spinal reflex excitability and corticospinal excitability can be described as the ability to contract muscle conducted by the spine and brain, respectively. Typically, healthy individuals modulate or quiet down their spinal reflexes and rely more on the corticospinal excitability during more demanding balance tasks. However, evidence indicates that the individuals with CAI are unable to modulate spinal reflexes and shift control to brain, leading to reduced balance performance. Given that the calf muscle plays a crucial role in balance, improving proper supraspinal and spinal reflexive control of the calf muscle is imperative to balance maintenance of individuals with CAI. To improve balance function for those with CAI, many balance training programs have been implemented to improve static and dynamic stability and proprioception for those with CAI. The majority of findings indicate that balance training can be effective in preventing initial and recurrent ankle sprains. However, it is unclear if common balance training methods can restore the function of the CNS in those with CAI. Therefore, the purpose of this study is to determine the effects of balance training on the calf muscle spinal-reflexive excitability modulation, corticospinal excitability, and balance performance in individuals with CAI. The rationale for this study is that patients with CAI require effective rehabilitation that can restore their neurosignature and improve balance ability.

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