Cooling Off the Run With Water

Water is the most vital nutrient for sustaining life. Approximately 60% of our body weight is made of water. It helps in various critical functions of the body, such as regulation of body temperature and transportation of nutrients and waste products. Therefore, the body requires proper hydration for optimal functioning. Water is lost from the body through various processes such as perspiration from the skin, respiration, urine and excretion. Thus, adequate hydration is important to maintain the water balance of the body.¹

Dehydration and performance

Dehydration encompasses both hypo-hydration (dehydration prior to exercise) and exercise-induced dehydration (dehydration during exercise).2 Dehydration can impair both physical and mental functions.3 Athletes tend to lose 6% to 10% of the body weight through sweat, which eventually leads to dehydration if body fluids are not replenished. This can be experienced by athletes in terms of decreased performance, which comes from reduced strength and feeling fatigued, which eventually leads to demotivation. Activities such as marathons that involve rigorous training have a more severe effect of hypo-hydration.³

In addition, the loss of body water through sweat, as seen with exercise, causes decrease in blood volume, which in turn can increase the heart rate and lower the blood pressure.³

Therefore, a suitable hydration plan prior to a run is very important.

Estimating sweat loss and adequate fluid intake

Sweat loss for athletes can be monitored most practically by measuring the changes in body weight, with corrections made for fluid or food intake and urine loss. To monitor the changes in body mass, athletes need to weigh themselves before exercise in minimal clothing and then immediately after the training. Post training, they should towel dry and weigh themselves in the same clothing on the same set of scales. The weight of any food or fluid consumed should then be added to the calculated change in body mass, before the estimated urine loss is subtracted. This will provide an estimate of sweat loss during the training period.

Rate of sweat loss = Total sweat loss ∕ Duration of exercise

Hydration strategies

Here are a few tips that can help you keep well hydrated.

Start the run well hydrated to avoid dehydration during the run. Avoid over-hydration because this leads to discomfort due to bloating and increased urination, thereby hindering the performance.4 Dehydration should not amount to more than 2% loss of the body weight (i.e.,1 kg for a 50-kg person, 1.5 kg for a 75-kg person and 2 kg for a 100-kg person).
If you are passing urine less often than normal or if the urine colour becomes darker than what is normal for you, then you have dehydration.5
Develop a drinking plan for training and competition that is right for you, based on sweat loss as given in Table 1.⁶

During run

The glucose flow in bloodstream is maintained by the intake of carbohydrates (continuous dosage of 20-60 g/h throughout the run), if taken just before the run or during rest periods in a long run (more than 40 minutes).⁶
Sodium content is one of the important aspects in fluids consumed during the run, which lasts longer than 1 to 2 hours that can stimulate heavy sodium loss (i.e., more than 3-4 g of sodium).⁶

Post run

Salt and water lost as sweat have to be replaced as a part of the recovery process. Sports drinks and pharmacy oral rehydration solutions that contain sodium and electrolytes are helpful; however, many foods can supply the required salt. In all, 1.2 to 1.5 litres of fluid should be consumed for each kilogram of body weight lost. Post-run recovery is essential to get started for the next round.⁶

1. Je´quier E, Constant F. Water as an essential nutrient: the physiological basis of hydration. Eur J Clin Nutr. 2010;64:115-23.
2. Barr I. Effects of dehydration on exercise performance. Can J Appl Physiol. 1999;24(2):164-72.
3. Popkin BM, D’Anci KE, Rosenberg IH. Water, hydration and health. Nutr Rev. 2010;68(8):439-58.
4. Australian Sports Commission. Effective hydration strategies for sweat loss. Bruce, Australia: AIS Sports Nutrition; 2009.
5. Sports Dietitian Australia. Fact Sheet; Fluids in sport. Victoria, Australia: Sports Dietitians Australia; 2009.
6. Common wealth games federation. Nutrition for Athletes. London, UK: Common wealth games federation; 2010.