NEFL and brain injury: In boxers, NF-L levels in cerebrospinal fluid have been found to peak at 15 days and normalize after 3 to 9 months.22,23 Although no increases in NF-L levels were observed in a study of soccer players after a heading training session,24 increased levels of NF-L were found in athletes playing collision sports, such as American football25 and professional Swedish ice hockey.14 This study provides additional support for NF-L as a subacute concussion biomarker, with potential value even days after injury.