A Season of American Football Is Not Associated with Changes in Plasma Tau.

American football athletes are routinely exposed to sub-concussive impacts over the course of the season. This study sought to examine the effect of a season of American football on plasma tau, a potential marker of axonal damage. Nineteen National Collegiate Athletic Association (NCAA) football athletes underwent serial blood sampling over the course of the 2014-2015 season at those times in which the number and magnitude of head impacts likely changed. Non-contact sport controls (NCAA men's swim athletes; n = 19) provided a single plasma sample for comparison. No significant differences were observed between control swim athletes and football athletes following a period of non-contact (p = 0.569) or a period of contact (p = 0.076). Football athletes categorized as starters (n = 11) had higher tau concentrations than non-starters (n = 8) following a period of non-contact (p = 0.039) and contact (p = 0.036), but not higher than swimmers (p = 1.000 and p = 1.000, respectively). No difference was noted over the course of the season in football athletes, irrespective of starter status. Despite routine head impacts common to the sport of American football, no changes were observed over the course of the season in football athletes, irrespective of starter status. Further, no difference was observed between football athletes and non-contact control swim athletes following a period of non-contact or contact. These data suggest that plasma tau is not sensitive enough to detect damage associated with repetitive sub-concussive impacts sustained by collegiate-level football athletes.