More than half of our body is water, of which two thirds are found in intracellular spaces and the remaining third in extracellular spaces. Specifically in men 60-70% of its weight is water and in women in 50-65%. The reason is that women having a higher fatty percentage, since fat is anhydrous, they have a lower proportion of water.
In triathlon tests, mountain ultra-trail, BTT marathons, cycling laps, popular races or simply the long training days, smokes, liquid is lost, and above all, when the conditions are of great thermal stress: heat + humidity, such as in the Ironman of Hawaii. A question assaults us should we replenish liquids? how much?.
The answer is easy:
Neither little nor too much. But ... What is little? And too much? If we fell "short", do our performance decrease? Or worse, do we endanger our health? And if we happen ... would the same happen?
Fortunately, to solve these doubts we have the science of our part and with a simple tool such as controlling the lost weight (most of it is liquid) during a competition / training you can move the “laboratory” to “track foot” every day and estimate the degree of dehydration and control the sweating rate of an athlete in a simple way.
Pre-competition hydration
Hydration days before the competition is fundamental, especially when developing in thermal stress environments. The recently published "
Recommendations agreed on training and competition in heat”They indicate that the fluid intake should be 6ml/kg of weight every 2-3 hours (attentive to those long walks through the corridor fair without hydrating well !!) and half a liter approximately in the 2h prior to the competition with about 3 grams of sodium.
Hydration during - competition
Giving figures, laboratory studies indicate that weight losses below 2% do not affect performance, losses between 2 and 5% negatively affect aerobic physical performance (cramps, fatigue, confusion), and above that figure, great health problems (heat stroke) can be had. However, when these measurements have been carried out in real sports tests, instead of laboratory test, it seems that the figure on which sports performance is affected, can increase to an average of 3-4%, especially when the athlete is well trained and acclimatized.
To estimate the liquid replacement needs during exercise, the sweating rate needs to be known. In this way, an amount of liquid/hour should be drank during physical activity in such a way that the Sweat vs. deficit. Liquid intake does not exceed 2-4% of body weight (lower margin the lower the degree of training and adaptation of the athlete).
To know the sweating rate, 2 alternatives are proposed.
- Option A - Generic data
Different studies indicate that the average sweating rate during physical activation varies between 1.5 and 2.5 liters per hour.
As an example, in a half marathon test, sweat rates of 1.5 ± 0.3 l/h and in Ironman tests 0.8 ± 0.9 l/h during the cycling sector and 1 ± 0.6 l/h during the marathon during the marathon have been reported.
- B - Individualized Data
The sweating rate varies depending on the climatic conditions (cold vs. heat; dry environment vs. humidity), gender (women minor sweat rates than men) or with the degree of training of the athlete or acclimatization in the environment. For this reason, the same person can have different sweating rates throughout a season, depending on their degree of training, acclimatization and competition.
In order to prepare a good personalized and individualized fluid replacement strategy during exercise, it is necessary to know the “individual sweating rate” and adapt the needs intake of liquid to that rate.
Its approximate calculation is simple:
Sweating rate (l/h) = (Post activity -weight
The fluid replacement must be such to prevent weight losses at the end of the test being greater than 2-4%. In an average marathon you can lose 2.5% of body weight and in an Ironman 3.5% (1% in water + 0.5% on the bike + 2% in the marathon).
In general, indicate that in the drink to ingest during the test it is recommended that it contains sodium, approximately about 0.5 and 0.7 gr/l, being able to increase this amount up to 1.5 gr/l in heat and humidity conditions.
Post Hydration - Exercise
To recover the body from the dehydration state after a sports or training test, the best option is to replace liquids as quickly as possible, in the 60-90 minutes interval post-activity.
The amount to drink must be between 120 and 150% of the lost body weight, being more effective with the taking of fruits or adding slight amounts of mineral salts to the drink.
We end the post having talked about the recommendations of fluid intake for a severe state of dehydration. But is it possible to get intoxicated by drinking a lot of water? The answer is yes and is a phenomenon known as "hyponatremia" frequent in long -term tests and with an intake of adequate mineral salts. We will talk about all this in an upcoming post.
We hope these lines have liked and it has been useful.
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Dr. Guillermo J. Olcina Camacho
226ers director - Endurance Research Lab.
Gaedaf Research Group Director at the Faculty of Sports Sciences. University of Extremadura.
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References
- Del Coso, J., González, C., Abian-Vicen, J., Salinero Martín, J. J., Soriano, L., Areces, F.,. . . Calleja-González, J. (2014). Relationship Between Physiological Paramers and Performance During Half-Ironman Triathlon in the Heat. J Sports Sci, 32 (18), 1680-1687. DOI: 10.1080/02640414.2014.915425
- OPPLIGER, R. A., & BARTOK, C. (2002). Hydration Testing of Athletes. Sports Med, 32 (15), 959-971.
- Racinais, S., Alonso, J. M., Coutts, A. J., Flouris, A. D., Girard, O., González-Alonso, J.,. . . Periard, J. D. (2015). Consensus Recommendations on Training and Competing in the Heat. BR J Sports Med, 49 (18), 1164-1173. DOI: 10.1136/BJSports-2015-094915
- Sawka, M. N., Burke, L. M., Eichner, E. R., Maughan, R. J., Montain, S. J., Stachenfeld, N. S., & Medicine, American College of Sports. (2007). American College of Sports Medicine Position Stand. Exercise and fluid replacement. MED SCI Sports Excer, 39 (2), 377-390. DOI: 10.1249/MS.0B013E31802CA597
- Sharwood, K. A., Collins, M., Goedecke, J. H., Wilson, G., & Noakes, T. D. (2004). Weight Changes, Medical Complications, and Performance During the Triathlon. BR J Sports Med, 38 (6), 718-724. DOI: 10.1136/BJSM.2003.007187
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Weschler, L. B. (2005). Exercise-Associated Hyponatraemia: A Mathematical Review. Sports Med, 35 (10), 899-922.
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