Abstract
ObjectivesThe potential effects of exposure to repetitive subconcussive head impacts through routine participation in sport are not understood. To investigate the effects of repetitive subconcussive head impacts we studied boxers following customary training (sparring) using transcranial magnetic stimulation (TMS), decomposition electromyographic (EMG) and tests of memory.MethodsTwenty amateur boxers performed three 3-min sparring bouts. Parameters of brain function and motor control were assessed prior to sparring and again immediately, 1 h and 24 h post-sparring. Twenty control participants were assessed following mock-sparring.ResultsOne hour after sparring boxers showed increased corticomotor inhibition, altered motor unit recruitment strategies, and decreased memory performance relative to controls, with values returning to baseline by the 24 h follow up.ConclusionRepetitive subconcussive head impacts associated with sparring resulted in acute and transient brain changes similar to those previously reported in soccer heading, providing convergent evidence that sport-related head impacts produce a GABAergic response. These acute changes in brain health are reminiscent of effects seen following brain injury, and suggest a potential mechanism underlying the damaging long-term effects of routine repetitive head impacts in sport.
Highlights
Across the sporting world there is growing concern about long-term health outcomes of traumatic brain injury
There was a significant alteration in the relationship between average motor unit firing rate and motor unit recruitment threshold between slope coefficient and y-intercept (p = 0.028; F(2.21, 39.79) = 3.76 and p = 0.035; F(2.88, 51.85) = 3.13, respectively – Figure 3) as a function of time, caused by a decline in the slope coefficient 1 h post sparring compared to baseline (p = 0.011; CI = −0.29 to −0.03) and immediately post sparring (p = 0.008; CI = −0.27 to −0.04 – Table 1)
We hypothesized that repeated sport-related routine head impact produces multi-modal brain changes suggestive of a GABAergic response
Summary
Across the sporting world there is growing concern about long-term health outcomes of traumatic brain injury. Recent evidence suggests that repeated exposure to both concussive (Wilson et al, 2017) and subconcussive head impacts (Smith et al, 2013; McKee et al, 2014, Ling et al, 2017) can affect long-term brain health. Relatively little attention has been paid to understanding mechanisms by which these chronic effects arise. The origins of long-term damage must first be evident in acute brain changes. The focus of the current paper is to characterize the acute brain alterations that occur following routine head impacts in sport.
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