Fluid & Training

ESSENTIALS

Fluid Intake

Flexibility

NUTRITION
Introduction

Carbohydrates
Fats
Proteins

Vitamins & Minerals

LIFESTYLE
Rest & Sleep

Smoking

COMPETITION
Goal Setting

Race Day
Warm Up

Temperature Regulation During Exercise

During exercise, when the rate of energy utilization rises, the rate of heat production also increases. So in order to prevent an excessive rise in body temperature your body produces sweat.

  The evaporation of sweat is a very effective way of loosing heat – for every 1 litre of sweat that evaporates, some 600 kcal of heat is released from the body. It is possible to loose as much as 2 litres of sweat during a one-hour training session.

  Although sweating is a very effective way of loosing heat, care must be taken to ensure that dehydration doesn’t impair this process. Sweat is simply a diluted version of blood so, when sweating is prolonged or pronounced, the body looses both water & electrolytes (salts dissolved in the body’s fluid).

  Water loss will cause serious problems if no attempts are made to replace the lost fluid. Losses of fluid corresponding to as little as 2% of the body weight can seriously impair the body’s capacity to perform muscular work.

  The body needs to balance the loss and intake of fluids in order to maintain its capacity to regulate body temperature, just like a car needs cooling fluid in the radiator. A reduction in cooling fluid will lead to a reduced ability to remove heat from the engine (the muscles) and deliver it to the radiator (the skin) where heat can be lost. Consequently, the temperature of the system will rise until the engine ceases to work.

  Something similar happens in humans when sweat losses greatly exceed replacement:

Ø      The circulatory system is unable to cope and skin blood flow falls. This is because the plasma volume must be persevered in order to maintain the high flow to the working muscle (to deliver oxygen to the muscle & remove the end-products of the energy metabolism).

Ø      As sweating continues the sweating continues, the water proportion of the body decreases, reducing the amount of blood available to the circulation and making it more difficult to satisfy the energy demands of the muscle and to transfer heat to the environment via the skin.

Ø      As a result of reduced plasma volume, the amount of blood pumped around the heart with each beat drops. Heart rate then increases and the blood flow to the skin decreases because blood flow to the muscle takes priority.

Ø      A reduction in sweating and the ability to loose heat accompanies this so, if exercise continues, the temperature of the body climbs steadily from normal to the danger zone: 41°C/105°F.

  In practical terms, the performance falls off rapidly at this stage and the effort required to maintain the same exercise intensity increase dramatically – even if the individual does not feel particularly hot. This may lead to exhaustion, with potentially fatal consequences, if action to correct the fluid imbalance and reduce heat production is not taken immediately.

When to take fluids

It is imperative that you train your body to except fluids whenever you exercise and you should be accustomed to consuming fluid at all exercise intensities, in both training and competition.

Thirst in itself is a very poor indicator of the need to start taking fluid. By the time the athlete feels thirsty, the losses of fluid during exercise are irreplaceable. So ensuring that the body is fully or over hydrated prior to exercise – never dehydrated – and then taking small amounts of fluid little and often from the beginning is of the up most importance. 

What influences water absorption?

  Water is mainly absorbed from the intestine, very little from the stomach itself. Once the water reaches the stomach, absorption is rapid and relatively unaffected by exercise. So the main limitation to fluid replacement seems to be not how quickly you can drink but how quickly the drink can leave the stomach. Many factors have been show to affect this process (known as the rate of gastric emptying), including how much you drink, its temperature and how hard you are exercising. The relative concentration of any substances, such as electrolytes and carbohydrate, dissolved in the drink will also significantly affect the process.

The factors influencing gastric emptying suggest the best way for athletes to rapidly absorb fluid:

Ø      Although larger volumes (up to 600ml) are emptied from the stomach more rapidly that smaller portions, athletes find it uncomfortable to exercise on a full stomach and it tends to interfere with breathing – most prefer to drink little and often. How much you should drink will depend on you, what solution you are drinking and how hard you exercise.

Ø      Colder solutions empty the stomach more rapidly than warm ones – the ideal temperature appears to be 8 – 15 C°- but don’t worry about chilling your stomach: stomach cramps are more likely to be the result of an over concentrated solution in your stomach rather than a cold drink.

Ø      The duration of exercise seems to have little effect on the rate of gastric emptying, but the intensity is very important. Up to around 75% of your maximum heart rate absorption seems to be unaffected but after that it declines rapidly.