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Hydration and Sports Performance

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Hydration and Sports Performance


Dehydration can compromise performance in high-intensity as well as endurance training and racing.

Drinking during exercise lasting more than 40-60min can improve performance. The reason for encouraging drinking is the consistent observation that dehydration in excess of 2% body mass (i.e. 1.5lt for a 70kg individual) impairs exercise performance by affecting the ability to perform aerobic exercise. Drinking water is generally better than drinking nothing, but carbohydrate (CHO)-electrolytes drinks are generally more effective than plain water.

During hard exercise and/or in warm weather an athlete might lose more than 1000mg of sodium per day, through sweat. The loss of sodium and fluids together triggers a chain reaction which results in reduced blood volume. Lower blood volume causes lower blood pressure, which usually will reduce the ability of the system to function at optimal level. A common physiological result of this sodium loss is muscle cramps, particularly in the lower leg and calf muscles. Therefore, fluid replacement is an important strategy for sustaining exercise performance.

How do we know how hydrated/dehydrated we are? Thirst is a good barometer, as is the color of your urine : it should be the colour of pale straw. A more precise way of measuring fluid loss during exercise is to jump on a scale before and after a training session. For example, if an athlete lost 1kg in training, that equates to a liter of fluid. If the athlete had 500ml of drink in the session, he/she will have to have an extra 500ml. It is recommended not to drink more than 750ml an hour, in order to avoid bloating.

But careful!! Drinking too much water, pure water not containing any salts or carbohydrate however, can produce adverse consequences and persistent drinking while sweating can result in exercise-associated hyponatremia, a potentially lethal condition. Drinking in excess of sweating rate should therefore be avoided.




Sports drinks are beverages whose stated purpose is to help athletes to replace water, electrolytes and energy during and after training or competition.

Isotonic sport drinks, such as SIS GO Electrolytes, contain similar concentrations of salt and sugar as in the human body.

The concentration of sugars and salts (osmolality) of ingested fluid is important as it can influence the rates of both the gastric emptying and intestinal water flux. Both of these processes together will determine the effectiveness of rehydration fluids at delivering water and electrolytes for rehydration and carbohydrate for energy.

Both Carbohydrate and Electrolytes have a role in promoting water uptake by the small intestine.

Carbohydrates (CHO): as well as providing energy for the working muscles, the addition of carbohydrates to ingested drinks will promote water absorption in the small intestine, provided the concentration is not too high. Amount and types of CHO present in a drink will influence its efficacy when consumed during exercise. The optimum concentration of CHO to be present in sport drink will depend on individual circumstances, but a high CHO concentrations will delay gastric emptying and therefore prevent energy to reach the gut to be absorbed to produce energy. The carbohydrate solution should therefore be isotonic: generally 6% carbohydrate with electrolytes.

Electrolytes: Performance is not only compromised by >2% body loss from water, but also by excessive change in electrolyte balance. Sodium is the major electrolyte present in sweat and the one important to replace. The other electrolytes are potassium, calcium, and magnesium. Sodium is essential for the maintenance of optimal fluid level within the body, since sodium levels determine how much water will be retained in the body and how much water will be excreted as urine. Sodium stimulates sugar and water uptake in the small intestine and will help to maintain extracellular fluid volume.


  • Make sure you’re well hydrated before you exercise, and keep drinking during your workout. Start exercise well hydrated, pre-exercise hydration can be assessed by urine color (check urine color= pale!) (NUUN/OTE are good products)
  • The goal of fluid replacement should be to prevent water loss (dehydration) in excess of 2% body mass during activity: drink sufficient to restrict body mass loss to not more than 1-2% of the initial value.
  • For more than 90min –electrolyte drink and gels 6-8gr CHO /100ml ISOTONIC (SIS GO advised)

There is an increased awareness of the need to individualise recommendations and for any guideline to be sufficiently flexible to meet athlete needs with very different physical characteristics and exercising in a range of environmental conditions. If you have any questions on the article, have any personal questions  or are perhaps interested in a professionally tailored plan then you can contact Ludovica at nutrition@bikenut.co.uk.



About the Author:

Ludovica has a PhD in Immunology and is an IOC qualified Sports Nutritionist . She is also a BTF Level 2 Triathlon Coach who competes herself from Sprint to Full Ironman distance Triathlon.


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