Sweat is a little more than your body crying. Sweat is your body cooling you off after a job well done. Yes, sweat gives you that glistening look after a good workout. That glisten however is fluid –possibly a great deal of fluid- and it would be a good idea for you to replace it. Don’t sweat it: Your hydration strategy is here!

Losing a mere two percent of your weight in fluids will cause you to slow down, by about ten percent mind you. [1]




Not a good forecast for a nice afternoon run. We are, after all, approximately 65 percent water and we function beautifully that way. Yet we also have 2 to 4 million sweat glands from which we can lose it. But don’t reach out for that water bottle quite yet. Sweat is more than water alone. Sweat is a salty situation. You can lose anywhere from 400mg up to 1800mg of sodium per liter of sweat. This is not uncommon, especially for active individuals. [2]

The way you choose to hydrate is vital to maintain a healthy lifestyle and eight glasses of water a day isn’t going to cut it. Especially if we consider that you are indeed a unique snowflake, from the parents you selected to the activities you now choose to engage in. To make sense of it all and help you determine your own best hydration strategy we might have to drown you in a little sweat science.

Losing it: water losses during exercise

A healthy body is able to regulate water content within itself quite well. For one thing we have thirst, the brain’s mechanism prompting us to drink. We also have a pair of kidneys that will regulate how much fluid we lose in urine. These mechanisms are still maintained during exercise but they merit a bit more attention then. [4]

When we exercise our core temperature is elevated. Sweat will then be excreted to deal with the rise in heat. If we continue to exercise, or we crank up the intensity, we will sweat more profusely-our sweat rate increases. Unfortunately, there is a point were sweat can no longer keep up. In 1969 Wyndham and Strydom recognized that once you loss 3 percent of your body weight in fluid, core temperatures became disadvantageous for any kind of performance. [3]

We can lose up to 2 liters of water per hour during intense exercise. [4] To maintain fluid balance under such conditions we need to devise a hydration strategy to accompany our body’s own regulatory mechanism. Because cramping, fainting, rapid heart rate and even muscle contraction dysfunction is not something we would like during a competitive event. 1 Replenishing fluid losses adequately during exercise is key!

Everyone has a different sweat rate and consistency depending on your genetics, body size and composition, fitness level as well as the conditions and intensity under which you are exercising. So, yes, you will need to take a critical look at any recommendation given and see how you can make it suitable for you.

A reliable way of monitoring sweat rate is to weigh yourself with as minimal clothing as possible prior to your training. You will also need to take note of all fluid taken in and possibly that which is loss in urine. Finally you will weight yourself once again after training - after removing all the sweaty clothes, if publically acceptable of course. Then you can subtract pre and post exercise weight also making sure of adding in any fluid intake to the equation.

Now a kilogram of weight loss is equivalent to 1 liter of fluid. So if you find yourself 1 kilogram lighter at the end of your exercise session yet you consumed 1 liter of water during that time, you have lost 2 liters of fluids. This is to give you a guide of how much you should rehydrate with and it does not necessarily mean you must do so. Iron man finishers have generally loss a good deal of fluid weight. Again make sure to work with what your body is telling you. The National athletic trainers association also recommends assessing the color and volume of urine as an accurate measurement of fluid loss. [5]

According to a 1996 Position Stand from the American College of Sports medicine we should “stay ahead of our thirst”. We should drink 1.2 liters of fluids every hour we exercise, in addition to starting with at least 400-600ml before performing any athletic endeavor. In fact the recommendations were to not only replace fluids at the rate of loss, but to consume as much water as “tolerable”. It was their opinion that once you became thirsty you would have had already reached a 3% level of dehydration.

Bad news!

Let’s also add that the ACSM guidelines would like us to spread out our water intake, 200-300ml every 15-20minutes depending on intensity. [9]

According to researchers at the Department of medicine at Georgetown University medical center a formula based approach to hydration is inadequate. Guidelines are to be tailored to each persons need. [6] We are quite well adapted to deal with different stressors why should water loss be different when we know far too well of how capable the body is of maintaining water balance. This is not to say that we should not drink appropriate amounts of fluid during exercise. But that we should utilize above all follow thirst as a good indicator of fluid replacement. If the brain senses that it needs water it will inhibit salivary production which will make you mouth dry and prompt you to drink. [7,8]

According to Dr. Noakes from the Sports Science Institute of South Africa we shouldn’t ignore our own body’s requests for hydration, because we could run into problems. Dr. Noakes believes that by “following thirst” we will maintain our hydration status at adequate levels even while exercising. He believes this is also the case for endurance athletes engaging in long duration events such as Ironman races. He has found that most of them will drink voluntarily, about 500ml to 800ml per hour which is half of the ACSM’s recommendations!!  [7]

Beyond water: why electrolytes are a good idea

In sweat we also lose a great deal of electrolytes such as sodium, potassium, chloride and calcium. Electrolytes are minerals that are charged when dissolved in water. They determine osmotic gradients which will ultimately determine how fluids are distributed in the body at a given time. This means they are essential for hydration and we also want to restore them. Electrolytes enable proper electric conductivity in the body as well as muscle contraction. [10]



Two thirds of the water in our body is within the cell and the remaining third is outside. The flow of fluids in and out of the cell can be attributed in great part by the action of electrolytes. The primary electrolyte loss in sweat is sodium. The amount of sodium loss varies significantly amongst individuals ranging from 20 to 80mmols or 400mg to 1.8g per litter of sweat. This is a very broad range to consider. You will now if you are at the upper limits or what is called a “salty sweater” if you often stain your clothes when you sweat. Don’t be fooled though. You’re sweat might not be salty but if the amount of sweat produced is significant you might still be in that upper limit. [2,10]

Any sort of exercise lasting longer than an hour or high intensities should consider supplementing sodium loss. Sodium aids in energy production and nerve cell signaling. It also happens to be the primary electrolyte in the extracellular fluid. Were sodium goes water follows thus this electrolyte is crucial for hydration. The current guideline for athletes would advise to consume 500 to 700mg (20-30mmol) of sodium per liter of fluid lost. [10]

Another big player in all this is potassium, which happens to be the main electrolyte inside cells and thus is sodium’s partner in crime when it comes to water balance. It is estimated that potassium loss, depending on sweat rate and composition, is approximately 435mg per hour. Replenishment guidelines for athletes currently advise consuming 50-80mg per every 200ml of ingested fluid. [9]

Water metabolism disorders: dehydration and hyponatremia

Ah hydration! We dwell deep on the importance of fluid and electrolyte replenishment preventing the much feared dehydrated condition. Here’s the deal- If you were to lose more fluids than you consume you would have a greater than normal concentration of sodium in tissue fluids. Don’t get me wrong the body is always ready to re-establish order but eventually if you are not careful you can end up with heat stroke because of this. Remember the importance of water balance. It all starts when you get a dry mouth, skin and eyes which can then progress to muscle cramping, reduced gastric emptying and a serious decline in mental and physical performance. [9]

Dehydration is certainly a bummer and is of special concern in hot and humid environments. If you are not used to these conditions be aware that sweat rate will increase and so will the amount of sodium loss in that sweat. Yes, we must be careful to not lose too much fluid under all conditions, yet as is often the case; there is always a need for balance. One can certainly go overboard and over-hydrate, which has its own set of issues. [11]

Hyponatremia or “water intoxication” can be caused by consuming more fluids that the body excretes. What happens in this case is that extracellular fluid gets diluted, leading to a lower concentration of sodium ions outside the cell. Sodium and water will then enter the cell disproportionally causing swelling and eventually even seizures. Symptoms are very similar to those of dehydration or heat stroke and quite hard to differentiate unless the circumstances are known. [11]

Hyponatremia is extremely rare, however, in sports lasting less than 4 hours.

Researchers such as Dr Christopher Almond have brought this condition to light, in most recent years, due to studies such as the one published in the New England Journal of Medicine back in 2005. The study found that 63 runners out of the 488 finishers of the Boston marathon where hyponatremic. They suggest that excessive fluid consumption is causative, but not the only factor in this condition. Hyponatremia seems to be related to slower finishing times (more than 4 hours) and body size (really small or very large). [12]

Not to say that all active people should stop drinking water or possibly better, a sports drink during their events, but rather that they should all take a more moderate approach to hydration. Perhaps “drink as you get thirsty” (provided you have tinkered with this as part of your training) and no more than 800ml of liquid per hour, as Dr Noakes recommends. [7]

The Gatorade mentality: when you should choose a sports drink

It has been suggested that having a sports drink may prevent both dehydration and hyponatremia in active individuals. It is clear that the sodium in most sports drinks, around 0.3g to 0.7g, will help increase the sensation of thirst, water absorption and better redistribute fluids inside the body. Other electrolytes such as potassium, magnesium and calcium have also shown benefit yet should be added in small quantities. [13]

Now whether you choose water or a sports drink, if you drink too much there is always the risk of hyponatremia. Yet in 2001 Bob Murray, ironman himself and the director of the Gatorade Sports Science Institute back then, stated that opting for a good sports drink will certainly minimize the risk of both dehydration and hyponatremia when compared to only consuming water alone. [7]

"Our advice remains unchanged: Drink to minimize weight loss, but don't overdrink. And favor a good sports drink over water." –Murray.
When it comes to performance, it is clear that sports drinks of a variety of electrolyte, carbohydrate and protein ratios are of benefit. [14] These mixtures seem to help with absorption, digestibility and blood volume. Long duration endurance events and even high intensity interval like training are highly dependent on glycogen stores.

When considering the carbohydrate content of a sports drink you might want to look for a glucose and fructose solution, that will replenish both liver and muscle glycogen, and that accounts for 4-8% of the beverage. It is also possible to choose actual foods to refuel. But choose wisely. Soft drinks and juices have often have a carbohydrate content that excess 10% of the fluid and are low in sodium which may delay gastric emptying. You can choose to salt more natural carbohydrate sources such as sweet potatoes or even a little rice. [9]

Perspire but Perform: Different activities require different strategies

Fluid balance is crucial for any activity. Period. Even, if you are training inside a well air-conditioned gym. Strength and power can also decline with improper hydration. Just think that muscle is two thirds water. Every 10 -15 minutes you should be drinking some water, I don’t see the need much for sports drinks unless you are training twice-a-day or training more than an hour at a time. [10]

Team sports and activities are not exempt from considerable fluid loss. Playing outdoors in humid conditions or with a great deal of protective gear or both will increase sweat rate. Dehydration will decrease reaction time and power. It’s no wonder that, back in the 1960’s , the University of Florida’s football team were the first to experiment with Gatorade. Over-hydration is also a concern because taking off all that gear to urinate is definitely undesirable. If you are engaged in activities such as basketball or netball you might want to consider at what point you actually have time to hydrate. Preferably you want to drink small amounts of fluid periodically during the game to eliminate discomfort. Carbohydrate-electrolyte mixes have been shown to reduce the rates of perceived exertion. However, If you choose water just make sure you consume some form of salt carbohydrate after the game, or if you are able to tolerate it, during the game. [15]

5 Hydration tips to sip on

1. Make sure to hydrate throughout the day. This does not only refer to sipping on your water bottle all day. If you are eating with metabolic precision, have eliminated processed food, have normal blood pressure, and are quite active, there is no need to fear salt. Salt your food!

2. Before you start a good guide to have in mind is to drink 200-600ml of fluid. This is a guide! At least every couple of weeks take some time to assess how much weight you have lost immediately after a good training session. You can attribute this to fluid loss. This will give you a good idea of how to tackle your next workout.

3. Always consider the weather conditions, the intensity and duration of the workout as well as when u can sneak in a sip or two of fluid during your session. If it is anything lasting more than hour sodium replacement, 500mg per liter of fluid lost, is a good idea.

4. Drink according to thirst but also previous training experiences and an understanding of your own individual sweat rate and composition.

5. After you are done training make sure you replace all fluid deficits. If you sweat it, drink it back. The 4 to 6 hours following a workout are crucial for this to happen. Losses include water, sodium all the other electrolytes. This can certainly be achieved through food. So make sure you include some fruits and veggies in you healthy post-workout meal.

Happy sweating folks!




Ana Castilla is a biology major, studying for her PhD in nutrition at Nova Southeastern University, in Ft Lauderdale Florida. A certified Sports Nutritionist, a key presenter and author on many aspects of exercise training and nutrition, Ana is also a fierce CrossFit competitor.





References

1. U.S. Department of Agriculture, Agricultural research service. USDA national nutrient database for standard reference release 18.2005. www.ars.usda.nutrientdata.
2. Institute of Medicine. Dietary Reference Intakes: Water, Sodium, Chloride, Potassium and sulfate. Food and nutrition board. Washington, DC: National academic press;2004.
3. Timothy Noakes. Lore of running. Oxford university press.4th edition. 2003.
4. Heather Hedrick Fink, Alan E. Mikesky, Lisa A. Burgoon. Practical applications in sports nutrition. 3rd edition. Jones & Bartlett Learning; 2011
5. Casa DJ, Armstrong LE, Hillman SK, et al. National athletic trainer’s association position statement: Fluid replacement for athletes. J Athlet Train.2000: 35(2)
6. Runners -- Let thirst be your guide." PHYSorg.com. 16 Jun 2007. http://phys.org/news101190846.html
7. Noakes, Timothy Is Drinking to Thirst Optimum?Annals of Nutrition & Metabolism : 10.1159/000322697.(2011).
8. Hew-Butler, T. Verbalis, JG. Noakes, TD. Updated Fluid Recommendation: Position Statement from the International Marathon Medical Directors Association (IMMDA). Clin J Sport Med 2006;16:283–292
9. Michael N. Sawka, et al. American College of Sports medicine Position Stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise: February 2007 - Volume 39 - Issue 2 - pp 377-390
10. Maughan RJ, Shirreffs SM. Recovery from prolongued exercise: restoration of water and electrolyte balance. J sports Sci. 1997;15.
11. Almond, C. Shin, A. Fortescue, E. Hyponatremia among Runners in the Boston Marathon. N Engl J Med 2005; 352:1550-1556April 14, 2005.
12. Winger JM, Dugas JP, Dugas LR. Beliefs about hydration and physiology drive drinking behaviours in runners. Br J Sports Med. 2011 Jun;45(8):646-9. Epub 2010 Sep 28.
13. Coombes J, Hamilton K. The effectiveness of commercially available sports drinks. Sports Med.2000;29(3)
14. Peter G Snell, Sidney J Stohs, et al. Comparative effects of selected non-caffeinated rehydration sports drinks on short-term performance following moderate dehydration. Journal of the International Society of Sports Nutrition 2010, 7:28
15. Fritzche RG, et al. Water and carbohydrate ingestion during prolonged exercise increase maximal neuromuscular power. J Appl Physol.2000;88.

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