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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
NONE
Enrollment
30
Participants will undergo a 4-week balance training protocol modified from that described previously. Participants will undergo supervised exercise three times per week for approximately 30 minutes per session. The exercise consists of single-leg balance training, hop to stabilization, and hop to stabilization plus reaching activities as presented in Figure 1. Particularly, the levels of difficulty will be progressed with visual conditions (eyes open and eyes closed), time (sec), and base of support (floor and foam pad) while hopping distance (inches) for single-leg and hopping activities, respectively. These activities will be progressed in difficulty as participants become proficient at the task.
Center for Brain Research and Rehabilitation
Norfolk, Virginia, United States
Active Motor Threshold
Transcranial magnetic stimulation will be delivered to the primary motor cortex of each participant using a Magstim Super RAPID2 PLUS1 System. A Double Cone Coil will be positioned over the primary motor cortex's approximated representation of the soleus to deliver single-pulse stimulations. From the output of the soleus MEP, the spot that generates the highest electromyographic (EMG) amplitudes with consistency will be identified as the "hotspot". To acquire the active motor threshold (AMT), the average peak amplitude of the background EMG signal will be collected while participants conduct the single-leg balance without magnetic stimulus. AMT will be defined as the lowest stimulator intensity needed to generate 4/8 stimulations with soleus EMG activity 2 standard deviations above baseline EMG data.
Time frame: 1 year
Motor Evoked Potential
After testing active motor threshold (AMT) 8 stimulations at intensities of 100% and 120% of AMT will be delivered using single-pulse stimulations over the soleus "hot spot." The electromyographic activity of the soleus from each stimulation will be recorded as the motor evoked potential (MEP).
Time frame: 1 year
Corticosilent Period
From the same stimulations used to test motor evoked potential (MEP), we measure corticosilent period (CSP) as the time from the end of MEP to a return of baseline electromyographic activity of the soleus.
Time frame: 1 year
Spinal Reflexive Excitability Modulation
Spinal reflexive excitability modulation will be measured while the participants are in the prone position and a single-leg stance. As a first step, the spinal reflexive excitability during prone and single-leg balance will be determined using a ratio of the Hoffmann-reflex (H-reflex) to the muscle response (M-wave) (H:M). H-reflex and M-wave will be elicited by BIOPAC stimulator module with a 2mm shield disk stimulating electrode attached to the popliteal fossa to stimulate the tibial nerve. The stimulation will be progressively increased with 0.2V until the maximal H-reflex and M-wave are obtained. Five the maximal H-reflex and M-wave will be recorded to calculate the H:M ratio. The following formula will be employed to calculate the modulation of H-reflex: (Prone-Single leg standing H:M Ratio)/(Prone H:M ratio)×100
Time frame: 1 year
Balance function
Balance performance will be measured via a force platform (AccuSway Plus, AMTI, Watertown, MA, USA) by doing a single-leg standing. The force platform will be connected to the Balance Clinic software (AMTI, Watertown, MA, USA) to acquire the center of pressure (COP) data. Balance function testing will include two visual conditions (Eyes open vs Eyes closed) while participants maintain single-leg balance on the involved limb. Each condition will be conducted three 20-second trials. Averaged COP path length, area, and maximum velocity in anterior-posterior and medial-lateral directions will be utilized for the final data analysis. Rest intervals of 1 minute will be provided between each condition. Furthermore, subjects will be protected by the primary investigator to prevent falling from the base of supports. 3\)
Time frame: 1 year
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