Effects of recurrent subconcussive head impacts on balance control in contact-sport athletes
Date
2018-10-01
Authors
Black, Stephanie E.
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Abstract
Background: Subconcussion, a mild traumatic brain injury, is best defined and identified by a lack of observable symptoms after axonal injury from minor head impacts. Subconcussive impacts are believed to accumulate with increased exposure over time, and are likely prodromal in the manifestation of a full-blown concussion. As evidenced by changes to changes in cerebral neurochemistry and structure, it is apparent that although individuals who have accumulated subconcussion may present as asymptomatic for motor and/or cognitive impairment using current clinical assessment tools, there is indication of long-term neurological damage which is presently going unrecognized. Objective: For the reasons stated above, a more sensitive and objective assessment tool is required to assess and recognize prodromal concussion manifestation in at risk populations with the intention of preventing further chronic sequelae. Design: Multiple baseline, time-series with repeated measures. Methods: Balance and bilateral reflex variability was assessed at pre-season and at post-season. Results: The current study identified significant changes to static balance postures (taken from the Balance Error Scoring System) through an objective postural assessment of centre of pressure (COP) and Area of Ellipse (AoE) calculations using a low-cost balance board and basic software interface after a season of accumulated subconcussion in female varsity rugby athletes. Specifically, double stance on the floor worsened by 31% in COPAP (p=.025) and by 26% in COPT (p=.038) and tandem stance on an unstable foam surface worsened by 180% in COPML (p=.014), 175% in COPAP (p=.025) and 141% in COPT (p=.005) between pre-and post-season. Our results indicate that these outcome measures are sensitive and can discriminate underlying balance deficits associated with accumulated subconcussive impacts. An objective measurement of spinal cord excitability through bilateral fluctuations of the Hoffman (H-) reflex in the tibial nerve found significantly elevated pre-season Cross Covariance (CCV) values which were 3x higher than those of a neurologically intact control population, suggesting prior neurological damage in study participants. Conclusion: The current study provides a platform for future research investigating bilateral fluctuation in spinal cord excitability after accumulated subconcussion and confirms balance decrements related to subconcussion can be identified through sensitive and specific measurement tools.
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Keywords
Subconcussion, Centre of Pressure, Balance, Hoffman Reflex, Contact-sport, Athlete, Female, Rugby