In this second article on hydration we focus on some practical guidelines to ensure adequate hydration, including what, how much and when to drink.
How Much Fluid?
There are no official guidelines for fluid intake, although many health professionals advise children and adolescents to drink 1.5 litres per day (1) or to drink periodically “until you are not thirsty any more, and then another few gulps”. For the child younger than 10 years, the suggestion is half a glass (100 – 125 ml) beyond thirst and for an older child or adolescent a full glass (200 – 250 ml) beyond thirst. (2,4) More structured recommendations give a range of 13 – 1.5 litres of fluid for children aged 9 – 13 and 1.4 – 1.8 litres for those over 14 years of age. These recommendations don’t take account of exercise. (1)
Water is often described as the best choice of fluid, but there are situations when drinks containing carbohydrate can have an advantage.
- Children drink more fluid when carbohydrate is supplied in drinks with a variety of different flavours. (2)
- If the athlete hasn’t eaten anything before training, a carbohydrate containing drink will possibly help maintain blood sugar levels and fuel the muscles. (1)
The objective in training sessions lasting about an hour is to replace fluid and prevent dehydration and no extra fuel should be necessary. Water should therefore be suitable for these sessions. For training sessions lasting longer than an hour, or perhaps for very intense sessions lasting 30 – 60 minutes, a drink that provides carbohydrate (such as squash, diluted fruit juice or sports drink) is a better option than plain water. The advantages include:
- It provides carbohydrate to fuel the muscles during exercise
- The carbohydrate in the drink (provided it contains 4 – 8 g /100 ml) helps the fluid in the drink get absorbed more quickly (1)
Some of the energy drinks or even sports drinks also contain caffeine which is known for its ability to increase mental alertness and endurance performance. While caffeine is considered safe for use by adults, there is little research supporting its safety and effectiveness in young athletes. High doses can cause side-effects, e.g. an upset stomach, sleeplessness, dizziness, headaches and higher blood pressure. Young athletes may be very sensitive to caffeine and experience some of these side-effects. The negative effects can outweigh potential performance benefits. (1)
When to Drink?
To recover from any previous episodes of dehydration, young athletes should consume 400 – 600 ml about two hours before training or competition. Fluid intake should be continued through drinking small amounts often during the warm-up. (1)
During training, the muscles produce heat, which raises the body’s core temperature. To avoid the core temperature increasing excessively, the body use a system known as thermoregulation. Heat is transferred from the muscles to the blood and blood flow to the skin so that heat can escape into the atmosphere through the evaporation of sweat. The amount of fluid lost in sweat depends on the environmental temperature and humidity, as well as the intensity and duration of exercise. Warm, humid conditions, and the long, hard exercise, will increase fluid losses. Replacing these fluid losses is particularly important to prevent dehydration and its associated dangers. (1)
Athletes should be encouraged to start drinking early during their training session – within the first 30 minutes – and to continue drinking at regular intervals. They should not wait until they feel thirsty or experience symptoms of dehydration before they start drinking. For most people, thirst is not a reliable guide to fluid losses but indicates that dehydration is already present.
- Young athletes should plan their drinking strategy for each training session and competition. As a rule of thumb, they should aim to drink around 500 ml per hour – more in hot, humid weather or when exercising very strenuously. If they exercise for shorter time or at a lower intensity, they can drink proportionally less as the risk of dehydration will be smaller.
- Encourage young athletes to drink little and often during training, ideally every 15 – 20 minutes or during drink breaks.
- Make sure they have a water bottle (or two for longer sessions) and keep it within easy reach throughout training.
- To get a more accurate idea of their fluid losses, young athletes can weigh themselves before and after training. They should not lose more than 2 per cent of their body weight during exercise. (1)
It takes, on average, between 30 and 60 minutes for the body to rehydrate after exercise. The recommended intake of fluid during this time is 1.2 – 1.5 times the weight of fluid lost during exercise to compensate for the increased urine production that accompanies drinking large volumes of fluid. Therefore, for each 1 kg of weight lost during exercise, the athlete needs to drink 1.2 – 1.5 litres of fluid over the next hour. (1)
Some salt (sodium) is lost in sweat during exercise but this is generally quite a small amount, which can easily be replaced in a normal snack or meal, or a sports drink. Many foods contain sodium so there’s no need to add extra salt. (1)
SPORTS DRINKS vs ENERGY DRINKS
Sports drinks are designed to provide rapid fluid and fuel replenishment to the body during exercise. They are isotonic, containing between 4 and 8 g carbohydrate per 100 ml, plus electrolytes such as sodium and potassium. The carbohydrate in sports drinks includes different combinations of sugars such as glucose, sucrose and glucose syrup) and maltodextrin (complex carbohydrates derived from corn starch) to increase the speed of absorption of fluid and provide fuel for the muscle during exercise. The purpose of sodium in sports drinks is to stimulate drinking as salt makes us thirsty and help the body retain the fluid better. (1)
Energy drinks are often hypertonic with greater amounts of carbohydrate and often added substances, including combinations of caffeine, guarana, taurine, B vitamins and various herbs. The sugar concentration is higher than that of sports drinks, around 10 – 12g per 100g, or 25 – 31g per 250 ml can. These drinks can stay in the stomach for longer and so do not provide an efficient way of rehydrating the body. (1)
|KEY MESSAGESYoung athletes should monitor their fluid intake and be aware of specific fluid recommendations.
Young athletes should start exercise well hydrated and should aim to maintain hydration status during training or competition by drinking if necessary.
After significant sweat loss, water and electrolytes should be replaced. (3)
1. Bean A. (2010) Anita Bean’s Sport Nutrition for Young Athletes. A & C Black. London.
2. Bass S & Inge K. Nutrition for special populations: Children and young athletes in Bourke Clinical Sports Nutrition
3. Meyer F, O’Connor H & Shirreffs M. (2007) Nutrition for the young athlete. Journal of Sports Sciences 25 (S1), S73-S82.
4. Unnithan VB & Baxter-Jones ADG. (2000) The young athlete. In Nutrition in sport Volume VII of the encyclopaedia of sports medicine. (edited by Ronald J Maughan). 429-441. Blackwell Science Ltd. London.