Particularly detrimental is a condition known as "second impact syndrome" where the player sustains an additional head injury before recovering from the first. According to Levine, the first blow may throw off the athlete's coordination and reaction time, increasing the risk and severity of additional hits.
"Even if when the second injury is mild it can be catastrophic," Levine said. "If a player at any level takes a hit to the head they should be removed from the game and not allowed back in until they've been cleared by a medical professional."
As an example of this, Levine referenced Zackery Lystedt, a Washington State middle school football player who suffered permanent brain damage after sustaining a concussion and returning to play. His case inspired legislation that requires players who show signs of being concussed to be removed from games or practices and not be allowed to compete again until they've been cleared by a trained health care professional. More than 30 states have adopted similar laws; the NFL and NCAA have lobbied lawmakers in 19 other states to enact similar legislation.
Levine said such laws plus a growing awareness and better training for coaches, players and medical staff, are slowly changing the culture of sports to better safeguard athletes against CTE.
Brian McCarthy, the NFL's vice president of communication, said in a statement Thursday that there is work to be done and the league is doing it.
"The NFL, both directly and in partnership with the NIH, Centers for Disease Control and other leading organizations, is committed to supporting a wide range of independent medical and scientific research that will both address CTE and promote the long-term health and safety of athletes at all levels," the statement read.
The statement noted that the NFL has contributed a $30 million research grant to the NIH, and looks forward to making decisions soon with the NFL Players Association on the investment of $100 million for medical research that is committed in the Collective Bargaining Agreement.
Levine said she was pleased the league had taken so many positive steps but these changes weren't likely to save the current generation of athletes who've already taken the big hits for far too long.
"Because CTE is degenerative and irreversible, once the damage is done, it's done," she said.