What do athletes drink during competitive sporting activities?

Although expert groups have developed guidelines for fluid intake during sports, there is debate about their real-world application. We reviewed the literature on self-selected hydration strategies during sporting competitions to determine what is apparently practical and valued by athletes. We found few studies of drinking practices involving elite or highly competitive athletes, even in popular sports. The available literature revealed wide variability in fluid intake and sweat losses across and within different events with varied strategies to allow fluid intake. Typical drinking practices appear to limit body mass (BM) losses to ~2 % in non-elite competitors. There are events, however, in which mean losses are greater, particularly among elite competitors and in hot weather, and evidence that individual participants fail to meet current guidelines by gaining BM or losing >2 % BM over the competition activity. Substantial (>5 %) BM loss is noted in the few studies of elite competitors in endurance and ultra-endurance events; while this may be consistent with winning outcomes, such observations cannot judge whether performance was optimal for that individual. A complex array of factors influence opportunities to drink during continuous competitive activities, many of which are outside the athlete's control: these include event rules and tactics, regulated availability of fluid, need to maintain optimal technique or speed, and gastrointestinal comfort. Therefore, it is questionable, particularly for top competitors, whether drinking can be truly ad libitum (defined as "whenever and in whatever volumes chosen by the athlete"). While there are variable relationships between fluid intake, fluid balance across races, and finishing times, in many situations it appears that top athletes take calculated risks in emphasizing the costs of drinking against the benefits. However, some non-elite competitors may need to be mindful of the disadvantages of drinking beyond requirements during long events. Across the sparse literature on competition hydration practices in other sports, there are examples of planned and/or ad hoc opportunities to consume fluid, where enhanced access to drinks may allow situations at least close to ad libitum drinking. However, this situation is not universal and, again, the complex array of factors that influence the opportunity to drink during an event is also often beyond the athletes' control. Additionally, some competition formats result in athletes commencing the event with a body fluid deficit because of their failure to rehydrate from a previous bout of training/competition or weight-making strategies. Finally, since fluids consumed during exercise may also be a source of other ingredients (e.g., carbohydrate, electrolytes, or caffeine) or characteristics (e.g., temperature) that can increase palatability or performance, there may be both desirable volumes and patterns of intake that are independent of hydration concerns or thirst, as well as benefits from undertaking a "paced" fluid plan. Further studies of real-life hydration practices in sports including information on motives for drinking or not, along with intervention studies that simulate the actual nature of real-life sport, are needed before conclusions can be made about ideal drinking strategies for sports. Different interpretations may be needed for elite competitors and recreational participants.