Quadratic Association Between Corticomotor and Spinal-Reflexive Excitability and Self-Reported Disability in Participants With Chronic Ankle Instability

in Journal of Sport Rehabilitation
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Context:

Spinal-reflexive and corticomotor excitability may have a critical role in altering muscle function needed to stabilize the ankle in people with chronic ankle instability (CAI).

Objective:

To determine the association between self-reported disability and both spinal-reflexive and corticomotor excitability in people with CAI.

Design:

Descriptive laboratory study.

Setting:

Research laboratory.

Participants:

30 participants with CAI.

Main Outcome Measures:

Soleus spinal-reflexive excitability was measured with normalized Hoffmann reflexes (H:M ratio), and corticomotor excitability was measured with transcranial magnetic stimulation and quantified by normalized motor-evoked-potential (MEP) amplitudes at 120% of active motor threshold (120%MEP). Self-reported disability was quantified with the activities-of-daily-living and sport subscales of the Foot and Ankle Ability Measure (FAAM-ADL and FAAM-S). Separate linear Pearson product–moment correlations and nonlinear quadratic correlations were used to determine associations between the neural-excitability and disability variables.

Results:

Thirty participants were included in the spinal-reflexive-excitability analysis, while only 19 were included in the corticomotor analysis. There was a significant, weak linear association between H:M ratio and FAAM-ADL (R = .39, P = .03) and a nonsignificant, weak linear association between H:M ratio and FAAM-S (R = .36, P = .06). There were significant, moderate quadratic associations between H:M ratio and both FAAM-ADL (R = .48, P = .03) and FAAM-S (R = .50, P = .02). There was a significant, moderate linear association between 120%MEP and FAAM-ADL (R = –.48, P = .04) and a nonsignificant, moderate negative linear association between FAAM-S (R = –.42, P = .07). There was a significant, moderate quadratic association between 120%MEP and FAAM-ADL (R = .57, P = .046) and a significant, strong quadratic correlation between 120%MEP and FAAM-S (R = .71, P = .004).

Conclusions:

There are significant quadratic associations between self-reported disability and both spinal-reflexive and corticomotor excitability of the soleus. CAI participants with low or high neural excitability present with lower function.

Harkey and Pietrosimone are with the Dept of Exercise and Sports Science, University of North Carolina at Chapel Hill, Chapel Hill, NC. McLeod is with the Dept of Health and Human Performance, College of Charleston, Charleston, SC. Terada and Gribble are with the Dept of Rehabilitation Sciences, University of Kentucky, Lexington, KY. At the time of this research, all authors were with the Dept of Kinesiology, University of Toledo, Toledo OH.

Address author correspondence to Matthew Harkey at Harkey@unc.edu.