The NFL has revealed that there were 13% fewer concussions in 2013 than during the previous season.
The league compiled data from the 32 teams' doctors from pre-season, regular season games and team practices, revealing that there were 228 concussions this season, compared to 261 in 2012.
The NFL's senior vice president of health of safety, Jeff Miller, told reporters: "Our perspective is that rules changes, culture change, the enforcement of the rules and the elimination, over time, of dangerous techniques is leading to a decrease in concussions. Now all of that said, we're talking about a small sample size of only a couple of years.
"This is an ongoing and important culture-change event, and so we're going to continue to analyse it and I think that there's room for continued growth. So we're pleased with the data, unquestionably, as it relates to concussion, but there's still more to do."
Players must pass a strict protocol before being allowed to return to the playing field after sustaining a concussion.