In American football, two-a-days occur when a team or individual trains on two occasions during the same day.
In the National Football League, two-a-days were eliminated in the 2011 collective bargaining agreement.
Those practices are called training camp, and most teams travel to distant locations to hold their preparations.
Heat stroke has become a major concern to football, and "two-a-days" are being red-flagged as a risky practice in places that experience traditionally hot weather in the summer.
The National Athletic Trainers' Association suggested similar guidelines in June.