The effect of playing career on chronic neurophysiological changes in retired male football players. An exploratory study using transcranial magnetic stimulation

Aim Repetitive head impact exposure, from contact and collision sports, are increasingly being attributed to increased risk of neurodegenerative disease in aging athletes. This exploratory study investigated the association of playing career in retired professional contact sport athletes with cortical neurophysiology via transcranial magnetic stimulation (TMS). Methods Male athletes between the ages of 28-68 years (n=113; mean age [SD] 48.8 [9.7]) who had been retired from professional sport for a minimum of five years were recruited. Cortical excitability was measured using single pulse TMS for motor evoked potentials and paired pulse transcranial magnetic stimulation short-interval intracortical inhibition and long-interval intracortical inhibition. Associations were assessed between transcranial magnetic stimulation measures and concussion history, clinical symptom scores, total career length (including junior to complete retirement), and professional career length (elite competition only). Results Correlations showed significant associations between motor evoked potentials and clinical symptom reporting ( rho -0.21 – -0.38; P <0.01); and motor evoked potentials and short-interval intracortical inhibition with total career length ( rho 0.26 – -0.33; P <0.01). No significant correlations were observed between single and paired-pulse transcranial magnetic stimulation and professional career length ( rho 0.16 – -0.15), nor the number of concussions ( rho 0.17 – -0.17). Conclusions This study is the first to report pathophysiological outcomes in a cohort of retired professional athletes associated with total career exposure, rather than professional career exposure or concussion history. TMS assessment could be considered a viable biomarker in future studies of retired athletes suspected with traumatic encephalopathy syndrome.