There are confusing messages about fluids. Sometimes you read that it is dangerous to drink too much, sometimes you read that drinking is essential to avoid dehydration. The truth is, both messages are correct; it is all about drinking the right amount, especially when playing in hot and humid weather conditions. Excessive dehydration or over drinking can both affect performance.

WHY ARE FLUIDS IMPORTANT?

During high intensity efforts, muscles produce a lot of heat, similar to how the engine of a car produces heat. The faster we run, the more we sprint, the more heat we produce. This heat needs to be dissipated to prevent the body from overheating. The main mechanism, especially when playing in hot conditions, is through sweating. Body fluids are a bit like cooling fluids in a car. If we lose too much of our cooling fluids, it becomes more difficult to control body temperature. And when we overheat performance can be reduced and in extreme cases we may develop heat stroke. So although some losses are not a problem, we must make sure we don’t run low on fluids.

COOLING THE BODY

The body can cool down in different ways. Avoiding direct sunlight and moving to the shade makes it easier to cool down. Wind or a fan will also help. Another way to cool down is through sweating. Especially in hot environmental temperatures, the evaporation of sweat from the skin is the most important mechanism. During intense exercise, the body loses 85% of its heat through sweating. Our skin has sweat glands from which sweat can evaporate. When it evaporates, it cools the skin and the blood in the skin. When it is very humid, it becomes very difficult to evaporate sweat from the skin and thus it becomes very difficult to cool down. In that situation, sweat will drip off the skin, diminishing the effectiveness of heat loss via this route.

Depending on conditions, you will lose body heat in different ways, but sweating is always going to be an important route during intense physical exercise, which means you will lose water from the body.

Sweat losses in soccer players have reported to vary greatly between players, even in response to the same exercise session in the same conditions. The two main determinants of the rate at which fluid is lost as a consequence of sweating (sweat rate) are exercise intensity and environmental conditions. Female players will generally have lower sweat rates than their male counterparts. The lower sweat rates are a consequence of smaller body size and less muscle mass contributing to metabolic heat production during exercise.

DEHYDRATION AND EXERCISE PERFORMANCE

As the body becomes more and more dehydrated, a reduction in blood flow to the skin and sweat rate may occur. With larger losses, it becomes more difficult to regulate body temperature. Several studies have shown, however, that mild dehydration, equivalent to the loss of 2% body weight can be sufficient to impair running performance in some conditions. In addition, it is often reported that greater losses in body mass will result in greater reductions in endurance, especially in hot conditions. Although dehydration has detrimental effects, especially on performance in hot conditions, such effects have also been observed in cool conditions.

In addition to the effects of dehydration on endurance, there are also reported negative effects on perception of effort, coordination and cognitive functioning. This is likely to have an impact on a player’s skill and decision-making process. Muscle strength and anaerobic performance are less likely to be affected by dehydration.

Soccer requires not only running (aerobic) performance, but also a sustained level of technical and skill proficiency throughout exercise. Some studies have shown that soccer-specific skill performance (e.g. dribbling) decreased with 2.5% dehydration, whilst performance was maintained with 1.4% dehydration. Other studies have demonstrated that dehydration of around 2.5% can reduce accuracy, speed of performing complex tasks, shot accuracy and distance judgement. For these reasons, staying hydrated is directly connected to performance during play. Figure 3 shows all the areas of performance that may be affected by dehydration.

On the contrary, some scientists have argued that some athletes can perform very well even when dehydrated. There may be discussion about the exact level of dehydration that is acceptable in soccer players, but since sweat losses don’t often exceed 2% body mass, and no extreme drinking routines are required in the vast majority of matches (excluding extreme conditions), 2% seems a practical and safe allowance for soccer players.

START HYDRATED

The allowable sweat losses above, assume that a player starts training or a game well hydrated. If you start already dehydrated, performance may suffer at smaller weight losses. Even though dehydration prior to training or games is easy to avoid, it is still very common for players to show up dehydrated. This can be prevented by drinking enough the hours before training or game. For more detailed guidelines, continue to read.

An easy way to check your hydration level is to look at the urine color before game or training. The color should be pale yellow and not dark. There is no need for urine color to be colorless. The urine color chart displayed in Figure 4 can be used for guidance. It is best to evaluate urine color when water intake and loss have been stable for a few hours. If you have just drunk a large volume, urine color may not reflect the bodies hydration level very well.

SIMPLE STEPS TO ESTABLISH YOUR HYDRATION LEVEL BEFORE PRACTICE OR A GAME

1. Collect a small urine sample in a clear container.
2. Hold your sample up to a light source and compare urine color to the colors in the chart.

1 – You are overhydrated; there is no need to drink this much. It may not be a problem but the extra water is just extra body weight.
2 or 3 - You are very well hydrated.
4 - You are normally hydrated or slightly dehydrated.
5 or 6 - You are dehydrated.
7 or 8 - You are extremely dehydrated.

3. If you determine that you are “slightly dehydrated,” “dehydrated,” or “extremely dehydrated,” consume more water, however, don’t overdo it.

TOLERANCE AND ACCLIMATION

Well-trained individuals seem to tolerate higher body core temperatures than less-trained individuals, and they are also better able to perform well in hot conditions. This effect is similar to the effect of heat acclimation which can protect significantly against the negative effects of hot environmental conditions. Heat acclimation means that your body is getting accustomed to the heat and this can be achieved by regularly training in a hot environment. A trained and acclimated person will sweat faster and more and is therefore able to control body temperature better.

ELECTROLYTES

With sweating the body loses not only water but also electrolytes. Electrolytes such as sodium, potassium, magnesium and chloride are the salts that can be found on clothing after training or games. The discussion in the media is often about electrolytes – which are good and important to replace – and salt – which is bad and intake needs to be reduced. They are in fact the same thing! The body has a certain amount of electrolytes and we do lose some with sweat. In soccer, the chances that we lose significant amounts of electrolytes in sweat such that performance is impaired or health is affected is very small. There is ample time after training or a match to replenish the electrolytes lost. Most meals will contain enough salt to accomplish this. Salt helps with water absorption from a drink and also makes you thirstier, which will ensure you drink more and helps you to stay better hydrated.

FLUID INTAKE BEFORE TRAINING AND GAMES

The aim for the player should be to start training and games well hydrated. Generally, there is sufficient time between training sessions or matches for the player to consume sufficient volumes of fluid with meals to achieve this.

As a guide, to ensure adequate hydration prior to exercise, players are advised to drink a volume of fluid specific for their body mass. Particularly, at least four hours before exercise, players should drink approximately 0.15-0.50 fluid oz. per pound of their body weight. On game days, this can be completed with the final meal before the game, whereas on training days (with morning training) these volumes should be ingested with breakfast. Consuming meals (food and drinks) containing small amounts of sodium will help stimulate thirst and the retention of the ingested fluid. By drinking approximately 4 hours before exercise, it allows sufficient time for urine output to return to normal before players are expected to perform. In addition, it avoids the situation of players drinking too much fluid immediately before exercise which increases the risk of player feeling bloated and experiencing gastrointestinal complaint.

In the situation where the player does not produce urine or the urine is of low volume and dark in color, a further 3-5 ml of fluid per kg of their body weight may be advised approximately two hours before exercise. It is important to note that fluid intake is, of course, self-regulated by the player. Therefore, adequate education programs within the club should be in place so that the player can identify signs of dehydration themselves and modify their drinking behavior appropriately.

FLUID INTAKE BEFORE TRAINING AND GAMES

In order to avoid significant dehydration during the match or training, fluids should be ingested in sufficient quantities. By regularly measuring body weight before and after exercise it is possible to build a profile of fluid losses in response to specific exercise sessions, i.e. training or games, and conditions (lower or higher temperatures and humidity). The next section will explain this in more detail.

Sufficient data collection over time will allow predictions of fluid losses based on exercise intensity and weather forecast. Fluid intake is likely to benefit the player when exercise is longer than 30-60 minutes, but there appears little advantage during strenuous exercise of less than a 30 minute duration. During shorter weight training sessions for example, drinking is not necessary.

On game days, the ingestion of large amounts of fluid is sometimes difficult because the opportunities for drinking during exercise are limited to before the game, half time and unscheduled breaks in play.

Excessive water intake should be avoided as this has been linked to hyponatremia (low plasma sodium). Although there have been no reported cases of hyponatremia in soccer players to date, education about the right volume of fluids to drink based on sweat rates – in combination with few drinking opportunities that exist both in training and on match days – should easily avoid the problem of over drinking.

Therefore, as a guide, players should aim to minimize fluid losses during exercise of an hour or more to equal to or less than 2% of starting body weight (assuming the athlete started in an euhydrated/balanced state). This goal becomes even more important when playing in the heat or in extended match play, i.e. extra time.

METHOD TO MONITOR FLUID BALANCE

Because of significant individual differences in sweat responses, it is difficult to give general advice that will work for every player. Therefore, it is recommended to measure sweat rates simply by measuring body weight before and after training or before and after a game. Start understanding your own individual characteristics and begin to implement drinking habits that are adjusted to your own individual needs.

Establishing whether a you drank enough is easy. Starting just before practice, follow these steps:

1. Void bladder.
2. Take a measurement of body weight (scale must be accurate to 0.2 lbs). This can be completed by players wearing minimal clothing, i.e. underwear or nude if privacy is possible.
3. After practice, don’t drink anything, dry off, before a final body weight measurement is recorded.
4. Now you can drink and visit the restroom.

Calculate, the weight loss by subtracting the weight after from the weight before. Express this as a percentage of body weight before. Use table 1 to look up if you need to drink more.

METHOD TO MONITOR FLUID BALANCE

If you also record how much you have consumed during practice, you can work out your sweat rate.

1. Write down the duration of practice.
2. Measure the weight of your bottle (or bottles) before and after practice (make sure that only you drink from this bottle and you don’t use water to spray over your head. The water in that bottle should only be used for drinking!
3. Convert all numbers to the units liters and (kilo)grams or use figure 5 to calculate your sweat rate.

WHAT TO DRINK?

Numerous studies have shown that “regular” water intake during
prolonged exercise is effective in improving performance. However, fluid intake during exercise also offers the opportunity to provide some fuel in the form of carbohydrate. Therefore during games where “performance” is the objective, the addition of carbohydrates to drinks consumed will have an additive and independent effect in comparison to water on exercise performance.

Beverages for fluid and energy replacement during exercise should:

1. Taste good to the player
2. Not cause gastrointestinal discomfort when consumed
3. Be rapidly emptied from the stomach and absorbed in the intestine
4. Provide energy in the form of carbohydrate and a source of electrolytes

It is for this reason that sports drinks typically have three main ingredients: water, carbohydrate and sodium. The water and carbohydrate provide fluid and energy respectively, while sodium is included to aid water absorption and retention. If other forms of carbohydrate are used – such as bananas, solid foods, chews or gels – it is recommended to combine these with water.

REHYDRATION AFTER TRAINING AND MATCHES

Rehydration is an important part of the post-exercise recovery process. In the post-exercise occasion, the ingestion of carbohydrate, fluid and electrolytes is required for replenishing depleted glycogen stores and rehydration. If players have accrued a body weight deficit (i.e. dehydrated), they should aim to completely replace fluid and electrolyte losses prior to the start of the next training session or match. In most cases players can just drink according to thirst as there is plenty of time to restore fluid balance before the next training sessions.

If dehydration is severe (>5% of body weight) or rapid rehydration is needed (e.g. less than 24 hours before next training or match or pre-season double training sessions) the replacement of fluid and electrolytes in the post-exercise period takes on greater importance. The main factors influencing the effectiveness of post-exercise rehydration are the volume and composition of the fluid consumed. The recommendation is to drink 45 oz. of fluid for each pound of body weight deficit. This is because some of the ingested fluid will be excreted in urine and studies indicate that ingestion of 150% or more of weight loss is required to achieve normal hydration within 6 hours following exercise. In most other situations, water and sodium can be consumed with normal eating and drinking practices with no urgency.

KEY POINTS

• Dehydration can have negative effects on the regulation of your body temperature and on performance.

• Dehydration can not only affect your endurance (how much you can run) but also your skill performance (accuracy, timing, decision making and so on).

• Small fluid losses up to 2% of your body weight are not problematic.

• Players should start training and games well hydrated.

• Urine color can be used as a simple check of hydration status.

• Just before and after half time drinks should be available especially if it is hot and humid.

• Players that sweat more than 2-3% should be identified and encouraged to drink so their losses are within 2%.

• The best drinks to hydrate are water and carbohydrate electrolyte drinks. Carbohydrates can have additional positive effects on performance.

• Excessive water intake should be avoided as this has been linked to hyponatremia (low plasma sodium).

• After exercise there is usually enough time to rehydrate, but if quick rehydration is required, drink 45 oz. of fluid for each pound of body weight deficit.

• Electrolytes are lost in sweat but can be replaced after exercise by the salt in our foods. Some of these losses can also be replaced by using a (carbohydrate)-electrolyte drink during training.

There are many questions about optimal nutrition for young athletes. Nutrition should support their normal growth and development, but also the increased needs as a result of training. It is also important to create good and healthy nutrition habits that will benefit any young athlete later in life. Nutrition is an important part of the athlete’s life, but unfortunately it is not always treated as such.

Young athletes are not just smaller versions of adult athletes. Young athletes have different nutritional needs because they are in a phase of growth, and their physiology and metabolism is different from adults. Here we will discuss the background, as well as some of the practical implications of nutrition for young athletes and their parents.

GROWING & DEVELOPING

The growth in height of pre-pubertal children between the ages of 2 and 10 years is linear and occurs at a rate of 2.4 inches per year. The median heights and weights for boys and girls are similar, averaging 2ft10 and 26.5 lbs at the age of 2 years to 4ft6 and 70lbs by the age of 10 years. The age for the onset of puberty varies among individuals. Puberty usually occurs in boys between the ages of 12 and 16, while in girls it generally occurs earlier, between the ages of 11 and 14. In some African-American girls, puberty begins even earlier, at about age 9. During puberty, large inter-individual differences exist in development. Children and adolescents need adequate energy intake to ensure proper growth, development, and maturation.

Dietary Reference Values (DRVs) have been established for various ages, but for the athletic or highly physically active child or adolescent, these recommendations will need to be adjusted for the level of physical activity. In adolescents in particular, the onset of the growth spurt, which is a major reason for increased energy requirements, is unpredictable and it is very difficult to estimate energy requirements. It is well known, though, that prolonged inadequate energy intake will result in short stature, delayed puberty, poor bone health, increased risk of injuries, and menstrual irregularities or absence in girls.

BEHAVIOR

It is important to educate children to eat a “healthy and balanced” diet and to encourage good eating habits. For the aspiring young athlete this should also include specific sports nutrition guidance with performance goals in addition to health goals. This can reinforce lifelong eating habits that contribute to the overall well being of children and may enhance sport performance. On the other hand, any bad habits developed in childhood and adolescence may be difficult to eradicate later in an athlete’s sporting career and should therefore be avoided. There is an important role for parents, coach and support staff to encourage appropriate eating behaviors, but also to avoid bad habits, such as too much attention to body shape and body weight.

For Parents:

•  Practice responsive parenting by discriminating hunger from other distress cues and avoid using food to comfort your child
•  Provide positive, repeated exposure to novel foods (especially typically rejected foods, such as vegetables) to promote acceptance of and preference for those foods
•  Offer developmentally appropriate and healthy foods to your child during the transition to solids
•  Serve portion sizes that are developmentally appropriate for your child’s age and nutrient needs
•  Choose when and what your child should eat, but let your child decide how much to eat
•  Trust a child of normal weight to self-regulate their intake
•  Make a wide variety of nutrient-dense rather than energy-dense, nutrient poor foods available and accessible to your child
•  Use your behavior and attitude to model healthy dietary patterns
•  Create a positive feeding environment by initiating regular family meals

Adapted from: Birch L, Savage JS, and Ventura A. Influences on the Development of Children’s Eating Behaviours: From Infancy to Adolescence. Can J Diet Pract Res. 2007; 68(1): s1–s56

DIFFERENT METABOLISM IN CHILDREN

There appear to be some differences in fuel use between adults and children. Children’s muscles are a bit more like the muscles  of endurance athletes (aerobic) and not yet developed for very high intensity (anaerobic) exercise. Children’s capacity to produce lactate is lower than adults and this means it is more difficult to sustain high intensity exercise. Children therefore rely very much on fat as a fuel than adults. These differences, however, seem to diminish throughout adolescence, especially in boys, suggesting that the hormones associated with puberty play a role in regulating energy metabolism in children.

PROTEIN

In order to support their growth and development, children and adolescents have protein requirements that are relatively high compared to adults. The Recommended Daily Allowances (RDAs) for protein in the United States are between 1.05 and 0.80 g/ kg depending on age with the highest recommendations for 1-3 year olds and lowest for 18 year olds.

However, as for adults, the protein requirements for young elite athletes are likely to be even higher. These requirements may be as high as 1.4 g/kg/day when young athletes play 10-12 h/wk. This would be around 75 g/d in this group, well above the RDA (52 g/d) for children of this age in the general population. However, when athletes are following a complete, well-balanced diet with adequate protein sources, this requirement is easily met with higher daily energy intakes of highly active individuals. In the United States protein intakes by children and adolescents are generally 2-3 times the RDA. On the whole, protein requirements seem to be of no particular concern for most young athletes. Nevertheless, it is important to be aware that there may be some individuals, who, perhaps due to intentional energy restriction for weight loss or a vegetarian diet, have protein intakes well below the recommended amounts.

CARBOHYDRATE

It is well known that carbohydrate ingestion in adults both before and during exercise can delay fatigue and improve endurance performance. Unlike protein, which has a quite general recommendation, recommendations for carbohydrate intake rate highly dependent on the intensity, duration and type of exercise that is performed by young athletes.

Although it is important to eat enough carbohydrate to fuel the activity, carbohydrate loading, such as is common practice in endurance sports to increase muscle glycogen levels, is not needed and not advised for children. Since generally their activities are shorter or require less glycogen and their ability to break down carbohydrate is limited, it must be questioned whether such    a strategy would be beneficial at all. A relatively high carbohydrate diet is advised but there is no need to follow a dedicated glycogen-loading regimen.

Children can benefit from carbohydrate intake during exercise, as adults do. But this is only useful when the exercise is high enough intensity and long enough duration. Many children will be physically active or engage in regular training but may not reach the level of physical activity that would warrant the use of carbohydrate beverages. However, those young athletes training hard and long enough will probably benefit.

FAT

Very few studies have investigated fat intake or fat requirements in physically active children. The usual general recommendation is that 25-30% of energy should come from dietary fat, but absolute fat intakes in g/d are highly dependent on the energy expenditure. As in adults, the main priorities are adequate protein and carbohydrate intake and fat can make up the remaining energy needs. Restricting fat intake in non-obese children has been suggested to impair growth and development, although it is not clear whether this is a direct effect of low fat intake or low energy intake. The quality of the fats also matters. Choose healthy fats and avoid trans fats.

FLUIDS

One of the main ways that humans lose heat is through the evaporation of sweat from the surface of the skin. As children have a higher ratio of body surface area to body mass (at the age of 8-years-old it is approximately 50% higher than that of an adult), it has been suggested that exercising children should be able to dissipate heat quicker than adults. This should give children an advantage in terms of their thermal homeostasis over that of exercising adults, at least up to the point at which ambient temperature exceeds skin temperature, after which this advantage is supposedly reversed. In practice, however, this has not been found to be the case and adults and active children seem to experience similar body core temperatures, even when exercising at high ambient temperatures. Whether the same finding would occur in young athletes, as compared to these active, but not competitive children, is yet to be determined.

High sweat rates in hot conditions can result in large fluid and electrolyte losses. In adults, the dehydration caused by this fluid loss has been shown to impair both motor control and physical performance, so adults are advised to balance any fluids lost from sweating, with fluid intake or to at least to limit losses to no more than 2% of body mass. However, there are large differences in sweat rates between children and adults. In fact, 9 year-old boys exposed to hot and humid conditions (45°C and 97% relative humidity) had an average sweat rate that was only half of that of men. This muted response, also observed in both young girls and adult females, is probably due to the underdevelopment of the peripheral sweating mechanism in younger boys. In fact, once male sex hormone production starts to increase during puberty, the sweat rate is seen to increase rapidly.

It seems tempting to speculate that if the young athlete’s ability to sweat is lower than that of adults, then their risk of becoming dehydrated during exercise in the heat will also be reduced. However, as sweating is the main way of dissipating heat during exercise, it is possible that children’s thermoregulation is less effective and their core body temperature could increase at a more rapid rate than an adults.

Studies show that the extent of dehydration, and more importantly, the risk of developing a heat-related illness seems to be similar between adults and younger athletes.

Thus the recommendations regarding fluid replacement are likely to be similar too. The policy statement by the American Academy of Pediatrics, regarding the fluid replacement guidelines for children during exercise in the heat state that a child who weighs 88 lbs should drink 5 oz. of cold water or flavored salted beverage every 20 min and an adolescent who weighs 132 lbs should drink 8 oz. every 20 min, even if the child does not feel thirsty. Such guidelines are very general and do not take into account important factors such as environmental conditions, exercise intensity, acclimatization and individual differences, but it gives perhaps a rough indication. At an elite level, it seems sensible to develop an individualized strategy that aims to reduce fluid losses in excess of 2-3% body mass. In general, involuntary hypohydration can reach up to 1-2% of body mass loss in boys and this in the vast majority of cases dehydration is not a major issue.

However, in hot conditions it is useful to occasionally measure body weight loss during practice (corrected for fluid intake) to identify individuals who lose more than 3% of body mass and may be under drinking. The reader is referred to the R2R document “Importance of Hydration” for guidance.

DO CHILDREN NEED SPORTS NUTRITION PRODUCTS?

There may be a small proportion of children that will benefit from sports drinks. These are the children that perform intense activity for longer periods of time and generally perform at a higher level. When performance on that day is the key focus, then a sports drink may be appropriate. For the vast majority of cases, water will do fine for hydration. The same is true for other sports nutrition products such as gels, chews, energy bars, and so on. These can sometimes be convenient solutions, but are not strictly necessary.

NUTRITION SUPPLEMENTS

While a number of young athletes may use nutrition supplements, you should promote a food first mentality. While a food first mentality is the preferred source of nutrients, when nutrients are lacking, supplementation may be an option in their nutrition. However, especially in young individuals, there must be reservations about most supplements regarding long-term use, combinations and appropriate dosages in an elite young athlete. U.S. Soccer has identified NSF- certified amino acids, multivitamins, electrolytes, probiotics, fish oil, and whey protein as supplements that may be considered in young athletes – only after consultation with a doctor, dietitian, or sports medicine professional.

We start with a food first philosophy. However, it may be challenging for athletes to design and put into action a complete fueling plan. Time constraints, access to fresh, whole foods and grocery stores, culinary and nutritional knowledge, underestimating the additional demands of sport, recovery, and growth, are all factors that may lead many athletes to fall short of the recommended levels of nutrients. We believe with proper education and safeguards such as NSF-Certified for Sport, supplements can be an option when food is not available.

WEIGHT MANAGEMENT

Perhaps one of the greatest potential threats to child health is inappropriate weight control in young athletes that could lead to the development of unhealthy eating behaviors, an eating disorder, or impaired growth and development. If a reduction in body mass is desired, this should be done gradually and limited to no more than 1.5% of body mass per week. A more rapid rate of weight loss than this will likely result in muscle protein breakdown, and this may interfere with growth and development. When possible, the athlete should be counseled by a registered dietitian who has experience of working with athletes and their families.

Contributors: Professor Asker Jeukendrup and Dr. George Chiampas

Youth Player Nutrition Guide