The Effect of Playing Career on Chronic Neurophysiologic Changes in Retired Male Football Players: An Exploratory Study Using Transcranial Magnetic Stimulation

Purpose: 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: This study used a cross-correlation design without a control group. Male athletes between the ages of 28 and 68 years (n = 113; mean age [SD] 48.8 [9.7]) who had been retired from professional sport for a minimum of 5 years were recruited. Cortical excitability was measured using single pulse TMS for motor evoked potentials and paired pulse for short-interval intracortical inhibition and long-interval intracortical inhibition. Associations were assessed between TMS 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 to −0.38; P < 0.01) and motor evoked potentials and short-interval intracortical inhibition with total career length (rho: 0.26 to −0.33; P < 0.01). No significant correlations were observed between single and paired-pulse TMS and professional career length (rho: 0.16 to −0.15), nor the number of concussions (rho: 0.17 to −0.17). Conclusions: This exploratory study is the first to report pathophysiologic outcomes in a cohort of retired professional athletes associated with total career exposure, rather than professional career exposure or concussion history. Without a control group comparison and cross-correlational design, these preliminary results should be viewed with caution; however, TMS assessment could be considered a viable biomarker in future studies of retired athletes classified with traumatic encephalopathy syndrome.