Players also experienced twice as many head impacts during the preseason as they did in practices and games in the regular season, the data showed.
The findings suggest that changes to policies and procedures regarding physical contact in general, and head-to-head contact specifically, during preseason practices could help reduce players' risk for concussions without "major modification to game play," the researchers said.
"The higher incidence of concussion in the preseason is likely due to several factors, including the total hours and intensity of training, heavy emphasis on full contact drills -- [such as] tackling, blocking, etc. -- and the volume of participants in those activities," study co-author Michael McCrea told UPI.
"Over the course of the season, it's common for football teams to reduce the frequency of full contact drills, thereby also reducing head-impact exposure and risk for concussion from full contact activities," said McCrea, co-director of the Center for Neurotrauma Research at the Medical College of Wisconsin.
The findings are based on an analysis of data on head impacts and injuries for 658 players at six Division I NCAA college football programs over a five-year period, according to the researchers.
The six schools were all participants in the Concussion Assessment, Research and Education Consortium, a partnership between the NCAA and the U.S. Department of Defense that is looking into the effects of concussions.
The 658 players, most of them starters on their respective teams, were fitted with an in-helmet Head Impact Telemetry System developed by sports equipment manufacturer Riddell.
The system uses in-helmet sensors to measure head impact frequency, location and magnitude.
Over five seasons, 2015 through 2019, the 658 players in the study sustained 528,684 head impacts, or an average of more than 400 per player per season, the data showed.
Sixty-eight players suffered a diagnosed concussion, with 49% reported during preseason, the researchers said.
There were 325 head impacts per team per day during the preseason compared to just over 162 per team per day during the regular season, according to the researchers.
"The overall number of practices and the volume of players participating in those drills compared to games suggests that reducing full contact activities in practice could do the greatest good in reducing incidence of head-impact exposure and concussion throughout the full football season," McCrea said.
"The most effective strategies will benefit from buy-in at the institutional level from athletic administration, coaches and athletes themselves," he said.