Hydration - what you need to know (2024)

Door Steve Born

How your cooling system works

When we exercise, we burn molecular fuel (especially glycogen). But we also burn some protein, fat and blood sugar from ingested nutrients. When these energy suppliers fail, heat is released. It builds up and increases our core temperature. The body must lose this heat and maintain a core temperature within a few degrees of the familiar 37°C. An active person needs a reliable cooling mechanism.

In fact, you have several. You lose some heat through your skin. Blood transports heat to the capillaries near the skin's surface and removes heat from the core of the body. You breathe harder to get more oxygen and dissipate heat as you exhale. But by far the most important part of the cooling system, accounting for an average of 75% of all cooling, is your ability to produce and excrete sweat.

Sweat glistening on your forearm or soaking your singlet won't cool you down. It must evaporate. Sweat works on a basic physical principle: water evaporation is an endothermic process that requires energy (heat) to change from liquid to gas. Water molecules in the gas phase therefore have more energy than water molecules in the liquid phase. When water molecules evaporate from your skin, they remove heat energy. The other water molecules have less energy and you feel cooler. Isn't it cool?

Weather conditions have a major influence on sweat production and cooling efficiency. In cold weather you will get significant cooling from the heat escaping directly from your skin. As temperatures rise, you become increasingly dependent on evaporation. On hot days, with little difference between skin surface and ambient temperature, your skin surface provides only negligible convective cooling and you will need to sweat more to maintain a safe internal core temperature. At 35° C or higher you lose no heat at all from your skin and you even start to absorb heat. Evaporative cooling should do all the work.

Humidity is the other major factor that affects sweat. On humid days, sweat evaporates more slowly because the atmosphere is already saturated with water vapor, which slows the rate of evaporation. The sweat collects on your skin and soaks your clothes, but it doesn't cool you down because it doesn't go into the vapor phase. Soaking, dripping sweat may give you a psychological boost, but it has no physical cooling effect. Sweat must evaporate to remove heat. On days when it is both hot and humid, you don't have to read what will happen if you train in those conditions. You should know that under the worst conditions, you can produce up to three liters of sweat in an hour of intense exercise, but your body can only absorb about one liter of fluid. Yes, this will cause problems soon and we will discuss that problem below.

What happens if the coolant runs out?

Just like a car, your body needs to dissipate the excess heat released when burning fuel. Unlike a car, your body's coolant is not contained in a sealed internal system. You use it once and then it's gone and needs to be replaced. Unfortunately, we don't have built-in gauges or indicators that tell us how much coolant is left in our system. We can't run a dipstick down the esophagus and get a reading that says, "add a quart." We have some physiological symptoms, but they work at 'Warning-Danger!' level, too late to maintain optimal performance. For example, if you are thirsty, you may have a water loss of 2% of your body weight, which is already in the exhaustion zone.

The diagram below shows what happens to human performance with each percentage of weight loss. By weight loss we mean the percentage of your body weight at the beginning of the training that you have lost through sweating at the end. If you start running at 160 pounds (about 72.5 kg) and 20 miles later you weigh 154 (about 70 kg), you have lost almost 4% of your body weight. It's too much to maintain your pace until the end, let alone expect to pedal.

Symptoms after water loss as a percentage of body weight:

• PERCENT WATER LOSS ---------- SYMPTOMS
• 0% --- none, optimal performance, normal heat regulation
• 1% --- thirst stimulated, thermoregulation during exercise changes, performance decreases
• 2% --- further decrease in thermoregulation, inhibits performance, increased thirst
• 3% --- more of the same (reduced performance)
• 4% --- training performance reduced by 20 - 30%
• 5% --- headache, irritability, "feeling of distance", fatigue
• 6% --- weakness, severe loss of thermoregulation
• 7% --- collapse likely unless training stops
• 10% - comatose
• 11% – death likely

[Nutrition for cyclists, Grandjean & Ruud, Clinics in Sports Med. part 13(1);235-246. January 1994]

How much is it?

As you can see from the chart above, sweat loss can easily escalate from an athletic performance problem to an acute medical problem. Clearly we need to have a quantifiable idea of ​​our intake and output. Let's start by converting the data in the graph into recognizable quantities. You may remember the saying: a pint is a pound, worldwide. It is now a convenient conversion for endurance athletes. Here's another: a pint = a water bottle. Some bottles hold 20 ounces (about 590 ml), but think of a regular water bottle as a pint (16 ounces/about 475 ml). Two pints make a liter (32 ounces), which is almost a liter – not quite, but almost. So when you read liters, think of two water bottles. Losing a pound (just under half a kilo) means losing a pint. A quart (or liter) is about two pounds (almost a kilogram).

Can you drink enough?

It goes without saying that maintaining optimal fluid intake before and during exercise is crucial for both performance and health. But as with calories and electrolytes, you can't replenish fluids at the same rate as you consume them. Your body simply won't absorb it as quickly as it loses it. Evaporative cooling depletes fluids and electrolytes faster than the body can replenish them. Your body accepts and uses a certain amount from exogenous (external) sources and similar to calories and electrolytes. Keeping fluid intake within a certain range will delay fatigue and promote peak performance.

Research shows that although the electrolyte needs of individual athletes can vary by up to 1000% (tenfold), fluid loss remains fairly constant. We can also measure fluid loss more easily than electrolyte loss. We don't need sophisticated laboratory equipment, just a scale. This allows us to get quite close to calculating fluid loss and replacement.

The numbers

On average, you lose about one liter (about 34 ounces) of fluid per hour of exercise. Extreme heat and humidity can increase that amount to three liters per hour. A trained athlete will store enough muscle glycogen to provide energy for approximately 90 minutes of aerobic exercise. When your muscles burn glycogen, water is released as a metabolic byproduct and excreted as sweat. Researchers found that runners released an average of two liters of sweat from muscle glycogen stores during a marathon (42.2 kilometers). This is in addition to sweat from other body fluids.

You can control or reduce these sweat rates by acclimatizing and training before the event. Acclimated athletes can reduce electrolyte and fluid losses by up to 50%, but keep in mind that these losses cannot be fully compensated during the event. Remember the words of Dr. Bill Misner (mentioned inLESS IS BETTER - The right way to burn goods*), the result of endurance training is to delay fatigue, not replace all the fuel, fluids and electrolytes lost during the event. It can't be done, even though many of us have tried. In other words, our hydration goal is not to replace water ounce-for-ounce or pint-for-pint, but to support the natural supply by consuming as much as we can adequately process during exercise.

You can absorb up to about a liter of water per hour, but only in the most extreme heat and humidity. Typically, you can only absorb about half or not too much of half that amount, even if it doesn't fully offset your losses. Repeatedly consuming one liter (about 34 fluid ounces) per hour will ultimately do you more harm than good.

Can you drink too much?

Ironically, even though you can't drink enough to replace all the fluids you've lost, you can still drink too much. Researchers have noted the dangers of over-hydrating during events that last more than four hours. Dr Tim Noakes spent ten years collecting data from around 10,000 runners who took part in the Comrades Marathon. This 84.33km race is held in South Africa every year in June (winter) and is considered one of the world's premier ultramarathons. Noakes showed that endurance athletes who consumed between 16 and 24 fluid ounces per hour (about 475 to 710 milliliters) typically replenished as much fluid as efficiently possible. He also noted the occurrence of hyponatremia (low blood sodium) during ultramarathons and triathlons in runners who overhydrated. This condition can arise from several physiological scenarios. In endurance athletes, this is usually due to sweat-depleted sodium stores that have been diluted by excessive hypotonic (low electrolyte) fluid intake. When the sodium concentration in the blood becomes too dilute, you can develop serious heart problems that lead to fainting.

Problems with too much or too little

Additionally, Noakes noticed a pattern of hydration problems among runners. In ultra events, the leaders usually dehydrate, but the athletes in the middle at the back of the pack tend to overhydrate. Both can ultimately suffer from the same hyponatremic symptoms. The former due to too little fluid intake combined with too much sodium loss due to excessive sweating, the latter due to too much fluid intake and relatively less sodium loss. Because most front runners are extremely competitive, they don't stop long enough to hydrate during the race. Moreover, it is very likely that top athletes are fitter and better accustomed to dealing with warm weather conditions. The tendency to hang around at aid stations and try to relieve symptoms of fatigue or heat by drinking too much water is a fault found in the majority of remaining athletes, those in the middle or back of the pack. These athletes may also be novices who have heard the mantra "drink, drink, drink" but haven't had enough experience to personally tailor their individual needs. After the 1985 Comrades race, 17 runners were hospitalized, nine of them with dilutional hyponatremia. During the 1987 Comrades Marathon, 24 runners suffered from dilutional hyponatremia. These athletes had a severely overloaded fluid intake, with the inevitable result being a completely disturbed physiology.

Tragic consequences

Hyponatremia is usually caused by drinking too much, especially when drinking fluids such as plain water or a sports drink that does not have the correct electrolyte profile. Exercise and fitness levels, weather conditions and undoubtedly biological predisposition also contribute to the development of this form of hyponatremia, known as water intoxication.

Unfortunately, we have to conclude that this condition has, directly or partially, led to the deaths of otherwise healthy runners at major American marathons. It is difficult for us to understand the grief of the families they left behind. These athletes took on a marathon to achieve a personal victory. Improper hydration cost them their glory day and also their lives. They collapsed and entered an irreversible state, resulting in uncontrollable cerebral edema, coma and death. We are reporting this to help prevent future tragedies. Overhydration is a very serious problem. Unlike dehydration, which will generally only result in painful cramps, possibly a DNF or, at worst, IV therapy, overhydration can set off a chain of ultimately fatal physiological consequences.

So how much, how often?

The extreme cases mentioned above are very rare. Less serious limitations often occur with excessive fluid intake. We don't have a graph for overhydration that is similar to that for dehydration. Plus, you probably don't own a scale or have regular access to weigh-ins along your training route. So how do you know when it's time to drink? You don't wait until you have a quarter less. A good hydration regimen starts before you even start.

Noakes believes that ingestion of hypotonic fluids of one liter/hour (33.8 oz/hour) is likely to cause water intoxication and dilutional hyponatremia. He suggests athletes might do better with a fluid intake of 500 ml/hour (about 17 oz/hour) for ultra events run in warm weather conditions. In the article “The Top Ten – The Biggest Mistakes Endurance Athletes Make,” Dr. Ian Rogers that 500-750 ml/hr (approx. 17-25 oz/hr) will meet the hydration needs of most athletes under most conditions. According to Dr. Rogers, “Like most things in life, balance is key.” The balance in most situations is likely to be fluid intake not much above 500 milliliters (about 17 ounces) per hour, unless the predicted losses are very significant. Other research suggests a similar consumption of 4.5-7.0 oz (about 133-207 ml) of water per 15 to 20 minutes of exercise.

Based on the available research, along with the thousands of athletes we have tracked, we have found that 20-25 oz/hr (approximately 590-740 ml/hr) is adequate fluid intake for most athletes under most circ*mstances. For lighter weight athletes or those training in lower temperatures, 16-18 oz/hour (approx. 473-532 ml) may be perfect. Heavier athletes or athletes competing in warmer conditions may consider intakes of up to 28 oz/hr (approximately 830 ml/hr). We also recommend that to prevent dilutional hyponatremia, fluid intake should routinely not exceed 28 oz/hr (830 ml/hr). The exceptions are heavier athletes, athletes who train at extreme levels (extended periods of time at a high percentage of VO2Max), and athletes who compete in harsh environmental conditions.

20-25 oz (approx. 590-740 ml) is the equivalent of the typical regular to large water bottle and is an excellent size to work with.

Think about your electrolytes and calories!

We noted at the beginning of this article that in addition to cooling, water also plays an important role in the transport of nutrients. Water consumption has a direct influence on the absorption of electrolytes and calories. You should consider the electrolyte content of your fluid intake, especially if you drink more than about 24 oz/hr (710 ml/hr). If the temperature and humidity exceed 21° C (70° F) and/or 70% humidity, we recommend that you take electrolytes before and during every hour of exercise. See the article for a full discussion of electrolyte needsELECTROLYTE SUPPLEMENTATION – Why It's So Important and How to Do It Right.*

Also avoid fructose or other simple sugar-based drinks and gels, especially when it's hot, unless you want to address a gastric emptying problem that can lead to nausea and other stomach disorders. Compared to complex carbohydrates, drinks or gels containing simple sugars (usually glucose, fructose and sucrose) require more fluid and electrolytes for efficient absorption. Because they need more fluid, you get fewer calories per unit of water. You should limit simple sugary drinks to a 6-8% solution range as they do not contain enough calories for energy production. You can make a good drink in a water bottle that is highly absorbent and contains enough fluid, but your calorie intake will fall far short of your body's needs and your energy levels will suffer.

If you're making a double- or triple-strength batch of a simple sugary drink in hopes of getting enough calories, you'll need extra fluids and electrolytes to process the sugar effectively. You have to guess how much extra water and electrolytes your body needs to process the sugar. Guessing low forces your gastrointestinal tract to pull minerals and fluids from other parts of the body. This scenario can cause nauseating results, as your body literally dries out its working muscles while your stomach swells. Why take such risks when your performance is at stake?

Your smartest choice is to use complex carbohydrate fuel, the carbohydrate source for all Hammer Nutrition fuels. Even at a concentration of 15-18%, these fuel sources are quickly absorbed and digested, do not require excess fluid for transport through the gastrointestinal tract and provide all the calories that your liver can process. For more details on fueling, see the article PROPER FUEL - Training and Racing Suggestions*

Multi-hour fuel bottles - A convenient way to monitor fluid and calorie intake

If you are going to exercise for several hours, a convenient and time-saving way to fuel up (while allowing you to monitor calorie and fluid intake with greater precision) is to make concentrated bottles for several hours of renewable energy or Perpetuem. This is discussed in the article **"The Hammer Nutrition Fuels" in the appendix of this book. However, since the topic here is hydration, it is appropriate to present this information now.

Each scoop of Sustained Energy and Perpetuem you put in a bottle reduces the volume of water by approximately 1.5 ounces (approximately 44 ml). For example, if you add two scoops of Perpetuem to an approximately 620ml water bottle, you will not get the same amount of actual liquid. It will be about 18 oz (about 502 ml), maybe even a little less. For some athletes 18 oz/hour is sufficient, but for many athletes this is not enough. Often more than 25-28 oz (about 740-830 ml) of fluid is required per hour. As a result, you will need to drink your entire fuel bottle plus plain water from another source. After a while, it can be difficult to accurately track your fluid intake because you are meeting your needs from two separate sources.

To make it easier if you are training for three hours or more, we recommend making concentrated fuel bottles for several hours. For example, if you are going to exercise for four hours and you know you need two scoops of Perpetuem to meet one hour of fuel, make a bottle of 8 scoops in a 21 ounce water bottle (approximately 620 ml). Now you have four hours of fuel in one bottle and this offers a number of advantages:

• Since you have four hours of fuel in one bottle, you only need to drink a quarter of that bottle every hour, meaning you don't have to drink an entire bottle of flavored liquid hour after hour.
• You don't have to stop every hour to make more fuel, because you have four hours on one bottle.
• You can drink plain water and enjoy it from another source (another bottle, hydration system) to cleanse the palate and meet hydration needs.

Yes, there is still some liquid in the 8-scoop/4-hour bottle of Perpetuem, but the amount is small: less than four ounces (about 118 ml) per hour for four hours. Does that small amount of fluid count toward meeting your overall hydration needs? Yes, but it's a small enough amount not to worry about if you keep your total fluid intake within our suggested guidelines (about 590-740 ml per hour). Additionally, there is some flexibility built into these hourly guidelines (+/- 3-4 oz or approximately 89-118 ml).

So with that in mind, a concentrated bottle of Perpetuem can be thought of as a calorie-only bottle, and you will meet your hydration needs with plain water from another source. The beauty of this, in addition to the other benefits previously mentioned, is that because you are meeting your calorie and fluid needs from sources that are independent of each other, you can measure your intake with greater precision.

So if your workouts last longer than three hours, try the multi-hour bottle of Sustained Energy or Perpetuem. You will find that it will be much easier to track both your calorie and fluid intake. It has been a winning strategy for thousands of endurance athletes.

Other ways to cool yourself in extreme heat

Although not directly related to actual water consumption, an external water application can help cool you down. A cold, wet towel, sponge, hose or spray on the head and upper body can effectively lower body temperature, especially during a one-minute break. If you're running, take a one-minute walk, pour water and drink something tasty. If you cycle, find a place for a good coast or an easy ride for a minute. The interruption of vigorous exercise allows the dissipation of internal heat. Combined with hydration and external water, this can effectively relieve heat stress so you can complete endurance events in warm weather. Fiercely competitive athletes may scoff at running, but when it comes to core temperature, nature gives you two choices: cool down or DNF.

Suggestions for fluid intake outside training or competition

Now that you have a good indication of your fluid intake during exercise, we can focus on two other considerations: how much you should typically drink throughout the day, and how to hydrate just before a run or workout. For your normal daily hydration needs (that is, outside of your exercise-induced needs), no research has definitively come to an RDA for fluids, but about 0.5-0.6 fluid ounces per day. pounds of body weight (about 33-39 ml/kg) provides a more accurate standard than the eight drinks per day usually recommended for everyone. Multiplying your body weight in pounds by 0.5-0.6 will give you the number, in fluid ounces, you should aim for daily. Geometrically, you would multiply your body weight in kilograms by about 33-39 and that will give you a good estimate, in milliliters, of what you should drink daily. Warning: If you have not been consistently following this recommendation, you can begin to gradually increase your daily water intake until you reach your target amount. If you increase your fluid intake too quickly, your body will be flooded with too much fluid too quickly, which can increase your risk of hyponatremia.

To meet hydration needs prior to a workout or race, a number of recommendations have been presented over the years. Here are the two that we think make the most sense, the ones that will meet hydration needs without putting you at risk of overhydrating:

• One liter of fluid (about 34 ounces) in the two hours before the start (about 17 ounces/500 milliliters per hour), stopping consumption about 20-30 minutes before starting the workout or race.
• 10-12 ounces (approximately 295-355 milliliters) of fluid every hour until 30 minutes before start (24-30 ounces total fluid intake).

Keep in mind that while these are our recommendations, you must determine what works best for your system and the specific logistics of the upcoming race or training session.

Personal data is the key to efficient hydration

We do not offer 'one size fits all' solutions. We offer careful and scientifically substantiated advice. We've given you some guidelines to help you assess and calculate your personal hydration needs. Each athlete is personally responsible for incorporating hydration, refueling and electrolyte replacement into his or her training program. You have to find out in practice – before the match – what works for you. Most of you will find that your final numbers are very close to our suggested starting points. For others, you may find that your needs for a particular event require significant changes in certain cases.

If you've spent money on a heart rate monitor, a multi-function watch, or a body fat monitor, and if you use them properly, you already have some serious training tools. We suggest that a good scale (preferably one that can measure in increments of less than one pound, such as a scale) could prove to be your most valuable fitness investment. Weigh yourself before and after each outing and carefully record the time, exertion level, mileage, weather, fluid, fuel and electrolyte consumption. Another low-tech tip: make sure you know the capacity of your water bottles and hydration packs. When you start recording your fluid consumption and weight fluctuations, you will have the data to accurately calculate your personal needs in this absolutely crucial area.

Final checklist, some quick tips and summary

1.) If you complete an event weighing the same or more than when you started, you are overhydrated. If you have lost 3% or more weight, you are dehydrated. Up to 2% weight loss is safe and reasonable.

2.) In very long events, such as a century bike ride, the average rider will lose a pound or more of energy stores (glycogen, fat, and muscle tissue) in addition to water, so factor that into your weight differential.

3.) Don't assume that you can drink unlimited amounts of water or fluid while exercising and expect it all to be absorbed and the excess lost in sweat or through the kidneys. Instead, you will feel bloated, thin your blood, urinate a lot, and develop water intoxication.

4.) Exercise to get fit in the heat. Heat acclimatization and fitness reduce fluid and electrolyte loss by up to 50%.

5.) Wear the lightest, most evaporative clothing you can afford. Cotton is not on the list. Many fibers today provide superior moisture transport and evaporation, allowing your sweat to do the work nature intended.

6.) Generally keep fluid intake between 20-25 oz (approximately 590-740 ml)/hour. For lighter weight athletes or those training in lower temperatures, 16-18 oz (approx. 473-532 ml)/hour may be perfect. Heavier athletes or athletes competing in warmer conditions may consider intakes of up to 28 oz (approx. 830 ml)/hour. If you think you need more fluids, experiment with it during exercise, keeping in mind that you need extra electrolytes. Regular fluid intake of more than 30 oz (approximately 890 ml)/hour increases the risk of dilutional hyponatremia.

7.) Use cold liquids as much as possible because your body absorbs them faster than hot liquids. Know where to find cold water along your training routes. Use frozen and insulated water bottles and hydration packs.

8.) The color of the urine can indicate the level of hydration. Dark yellow urine means low hydration. Pale to light yellow is good. Don't confuse the bright yellow urine you get after supplementing with vitamin B-2 (riboflavin) with the dark yellow urine that indicates overly concentrated urine.

9.) When exercising, avoid foods and fuels that contain low-chain carbohydrates. These simple sugar fuels require more fluid and electrolytes for digestive purposes. Also avoid carbonated drinks, as the gas inhibits absorption.

10.) Be careful with caffeine. When used correctly and sparingly, caffeine has ergogenic benefits. However, it acts as a diuretic, which can deplete fluid stores more quickly.

11.) During the hottest weather conditions, sponging yourself down with cold water while taking short periodic breaks from the race pace will provide relief from the heat.

12.) Know the symptoms of overhydration and dehydration. Stop immediately if you feel dizzy, nauseous or experience dry chills. No run or workout is worth risking your health.

CV

Dehydration and overhydration are common problems that affect far too many athletes, some with serious consequences. Armed with the guidelines in this article, along with practice and testing during training, your performance and health need not suffer. Instead, you will have an advantage over the vast majority of athletes who keep making the same mistakes over and over again.