Fluid intake to counteract sweat losses is important during long competitive events and especially in a hot environment, because a fluid deficit equivalent to >2–3% body weight loss is usually associated with:
- worsening of the difficulty of the effort1
- reduction in performance (Sawka et al., 2015)
- risk of hyperthermia3 etc.
The importance of hydration, carbohydrate feeding and electrolyte replacement2 during long-distance races is enormous, especially when the environmental temperature is higher(Burke, 2010; Hoffman et al., 2018). Body weight losses of up to 10% have been reported in marathon race winners in heat (e.g. Beis et al., 2012).
However, fluid intake at events that allow it involves a cost-benefit analysis, where the “cost” to the athlete is:
- the availability of supplies at stations during the race
- the time lost at the moment of deceleration for the acquisition and consumption of drinks/sports products
- the risk of causing gastrointestinal disorders after consumption
Water
A well-tolerated initial hydration schedule is ~400–800 mL/h.
Personalization is imperative and influenced by many factors, including:
- sweating rate
- sodium content in sweat
- exercise intensity
- body temperature
- ambient temperature
- body weight
- kidney function
During exercise follow the feeling of thirst.
During urination, observation of urine color is indicative of hydration status. In any case, it is recommended to restore 150% of the fluids lost.
Sodium
- 300–600 mg/h is recommended for athletes with a high sweat rate (>1.2 L/h) or for prolonged exercise >2 hours. Individualized consumption is needed here as well.
- Improved water replenishment is observed with a sodium content of ~1380 mg/L.
When conditions (temperature, intensity, etc.) require it, a more aggressive approach to in-match hydration strategies is recommended to deal with greater fluid losses, while in the hours before, consuming large amounts of fluids along with an osmotic agent (e.g. e.g. glycerin or sodium) can reduce the net fluid deficit that occurs during the race by helping to retain up to 600 ml of body water stores in the short term1.
In addition, the intake of reasonable amounts of cold/frozen beverages may theoretically contribute to improved thermoregulation (Jay & Morris, 2018).
A personalized and applied training match plan that optimizes fluid consumption within the conditions and opportunities of each event is more than necessary. Higher rates of hydration are recommended for faster, heavier athletes competing in hot environments and lower rates for slower, lighter athletes competing in cooler environments. Individualization is recommended for all levels of runners, including amateur athletes, who must also regulate their fluid intake.
It is noted that, on the other hand, amounts of fluids that exceed the athlete’s sweat rate are not beneficial and should be monitored for the risks of developing hyponatremia (Almond et al., 2005). Fluid intake recommendations for endurance athletes have evolved. In the past, the accepted theory was that “by the time you’re thirsty, you’re already dehydrated.” Increasing fluid intake, under the assumption that the thirst mechanism is an inadequate indicator of hydration, was a standard practice, and excessive fluid consumption was a significant risk factor for the development of hyponatremia. Lighter and slower runners are also at risk of positive fluid balance. Exercise-related hyponatremia occurring during or within 24 hours after physical activity is a serious health complication and one of the potential causes of athlete collapse. While sometimes asymptomatic, other times it presents with confusion, dyspnea, nausea/vomiting and gastrointestinal disturbances, hypoglycemia, hypotension, hyperthermia, delirium, and even coma and death.
In conclusion, despite practical challenges, elite athletes have managed to break Olympic and world records using strategic hydration and carbohydrate intake plans (Caesar, 2017; Hutchinson, 2017).
Some marathons, including the world record-setting Berlin 2018, have increased the frequency of feeding zones (every 2.5 km), which highlights the importance of the restoration of losses during sporting events
- Burke LM, Jeukendrup AE, Jones AM, Mooses M. Contemporary Nutrition Strategies to Optimize Performance in Distance Runners and Race Walkers. Int J Sport Nutr Exerc Metab. 2019 Mar 1;29(2):117-129. doi: 10.1123/ijsnem.2019-0004. Epub 2019 Apr 4. PMID: 30747558.
- Vitale K, Getzin A. Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. 2019 Jun 7;11(6):1289. doi: 10.3390/nu11061289. PMID: 31181616; PMCID: PMC6628334.
- Peeling, P., Castell, L. M., Derave, W., de Hon, O., & Burke, L. M. (2019). Sports Foods and Dietary Supplements for Optimal Function and Performance Enhancement in Track-and-Field Athletes, International Journal of Sport Nutrition and Exercise Metabolism, 29(2), 198-209. Retrieved May 8, 2023, from https://doi.org/10.1123/ijsnem.2018-0271
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