The two-a-day practice session is a part of both the folklore and the reality of American football training camps. It is a regimen and a rite of passage imposed on players competing at the high school level through to the professionals of the National Football League. At every competitive level, the American football season begins in September. Given the intensely physical nature of the sport and the technical demands of integrating distinct positions into a team concept, it is common for the preseason practices to provide both training volume and training intensity, all of which tends to occur in the warm weather months of July and August. Two-a-day practice sessions are designed to achieve those sometimes disparate training objectives.
The purpose of the two-a-day practice must first be considered with respect to the larger concept of season planning, known as the periodization of training. All competitive teams and individual athletes cannot train at a constant maximum level for an entire calendar year; the athlete and the team perform best when they are trained to peak for certain periods during the year, with an appropriate build-up to the peak performance, and a recovery and rebuilding phase to follow.
To properly account for the physical demands of American football, a properly periodized training schedule for a football team will consist of three general subdivisions: the preseason, the competitive season, and the off-season. Each of these segments will be further subdivided to address specific training or competitive issues that are anticipated to arise within each individual training period. As an example, an American college football team will commence its competitive season on approximately September 1 of a given year; the team may have aspirations of playing in a season-ending championship game in late December or early January, a competitive period of approximately four months. Once the season is completed, the players will be encouraged to reduce the level of their physical activities for four to six weeks to permit physical recovery. The players will then be expected to begin ever-increasing weight training and running workouts in preparation for spring practice in May. The players would return to individual weight and running workouts in the summer, to commence the preseason two-a-days in early August, with a new season beginning in September. The lead-up to the beginning of the two-a-day workouts would include a period of acclimatization to any expected warm weather conditions at the practices.
Heat acclimatization is usually achieved for an individual player within 10 to 14 days of commencement of the player's exposure to unaccustomed warm weather conditions. If plotted on a graph, the training periods would reflect both the amount of time and the intensity to be devoted to each workout segment.
With proper periodization of training, one of the key dangers of two-a-day football practices is reduced: the dramatically increased risk of injury due to improper conditioning leading up to the commencement of such practices. The second danger, a failure on the part of both athletes and coaching staff to ensure the proper hydration of the athletes during practices, is also one that may be minimized, if not prevented, through adherence to basic hydration principles. It is essential that the athletes engaged in such vigorous exercise be encouraged to consume water or appropriate sport drinks before, during, and after practice. The body's thermoregulation system is constructed in such a fashion that the thirst mechanism, located in the hypothalamus region of the brain, is activated after the body has become dehydrated. Encouraging athletes to consume fluids even where they are not thirsty combats this mechanism. The death of Minnesota Vikings football lineman Kory Stringer in 2003 at a two-a-day practice session as a result of heat stroke served as a warning to all teams conducting any type of warm weather training.
As a general rule, water, water with sodium or other electrolytes added, or sports drinks with a maximum of 6% to 8% carbohydrate are the most effective fluid replacement products in two-a-day practice environments. Sport drinks with greater than 8% carbohydrate tend to be absorbed more slowly in the body through the small intestine. The consumption of caffeine or alcohol during or after the practice period will contribute to dehydration as each of these substances acts as a diuretic, creating additional urine production and fluid loss. Urine color is a useful indicator as to whether the body is properly hydrated; light yellow urine is an indicator of proper fluid levels, and dark-colored urine is a symptom of dehydration, as the urine is overly concentrated.
The total amount of fluid to be consumed as a part of a sound hydration strategy at a two-a-day practice schedule will vary from person to person. As a general rule of thumb, most players should consume between 28 oz (800 ml) and 40 oz (1.3 l) of fluids for every hour they are involved in a practice or a game in the course of such workouts. Two-a-day workout effects are also reduced if the players have access to a cool area between practices, where they can reduce their body temperatures.
Two-a-day practices are not unique to American football; many endurance athletes, such as marathoners and triathletes, will train twice a day. Sports that are popular in warm weather countries, such as soccer, cricket, and rugby, will engage similar training issues. The football two-a-day in American football is of particular interest, given the inherent combination of intense physical contact, overall exertion on the part of the athletes, and warm weather environments.