Cortical hypoexcitability persists beyond the symptomatic phase of a concussion.
OBJECTIVE
The purpose of this research was to assess cortical excitability, voluntary activation of muscle and force sensation beyond the initial highly symptomatic period post-concussion (1-4 weeks post-injury). It was hypothesized that reduced excitability of the motor cortex may impair muscle activation and alter perceptions of force and effort.


METHODS
Eight concussed varsity football players were age- and position-matched with eight healthy teammates to control for training and body size. Healthy controls had not suffered a concussion in the previous 12 months.


METHODS
Paired-pulse transcranial magnetic stimulation was used to assess cortical excitability, voluntary activation was calculated using cortical twitch interpolation technique and sense of force was determined using constant-force sensation contractions.


RESULTS
The concussed group had lower intra-cortical facilitation (p = 0.036), lower maximal voluntary muscle activation (p = 0.038) and greater perceptions of force (p < 0.05), likely due to compensatory increases in upstream drive, than their healthy matched teammates.


CONCLUSIONS
Taken together, these findings suggest a state of hypoexcitability that persists beyond the immediate acute phase of a concussion and may result in neuromuscular impairments that would call to question the athlete's readiness to return to sport.
Department of Kinesiology and Physical Education, Wilfrid Laurier University , Waterloo, ON , Canada.
Kaley C
KC
Powers
Michael E
ME
Cinelli
Jayne M
JM
Kalmar
D056352:Athletes; D001924:Brain Concussion / Q000503:physiopathology*; D019054:Evoked Potentials, Motor; D056966:Excitation Contraction Coupling; D005538:Football; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D009044:Motor Cortex / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult