Hydration in the heat – how to survive?

STAYING HYDRATED

Staying hydrated is a much vaunted subject for runners, particularly in the warmer months. Even small levels of dehydration can impact performance, affecting your cooling mechanism and increasing your perception of effort. As you become more dehydrated your blood volume decreases, causing your heart rate to increase without any increase in work output. Your peripheral blood flow starts to shut down, allowing your body temperature to spiral upward. This limits your capacity to increase your effort level and increases your rate of perceived exertion. The mental effect is that you lose concentration, and the combined effect is that you are going to end up in a situation where your performance will suffer. This can easily be avoided through effective hydration, both before and during exercise.

CAN I HAVE JUST WATER AND NOTHING ELSE?

A misconception regarding hydration is that drinking water alone will keep you hydrated. In reality, as you sweat, your body loses electrolyte salts which are essential to control the fluid balance inside the body. There are two major factors that affect how readily fluid will be absorbed:

1. The rate at which the fluid drains from the stomach.
2. The rate of absorption in the intestine, which is affected by the concentration of electrolytes such as sodium and carbohydrates in the drink.

Prolonged heavy sweating can lead to significant mineral losses, particularly sodium. If you just drink water, which has no electrolytes, you can dilute the concentration of remaining electrolyte minerals in your body. This stimulates your kidneys to produce more urine to keep the concentration levels balanced, but means that you do not retain the required fluid within the body.

HOW MUCH TO DRINK?

If you are doing an especially demanding event then you should begin your hydration a couple of days before, to make sure that you are at optimum levels. Depending on how hard your session is, your sweat rate and the conditions you take need to take around 500ml to 1 litre of fluid per hour, ideally drinking a little and often. 150-200ml every 15-20 minutes is a good target to aim for. To gauge how much fluid you have lost during exercise, try weighing yourself before and after exercise. Each kilogram of weight loss indicates 1 litre of fluid loss. Adding the amount of fluid consumed during exercise will give you the total fluid loss. Keep in mind those hydration principles and think advance far enough!

Advice provided by Emma Barraclough – Performance Nutritionist

WHAT ABOUT HYDRATION IN THE HEAT?