Dehydration? Drink Up!

Despite what Rexona would have us believe, sweating is a normal and useful bodily function. Just like a radiator is vital for preventing your car from overheating, the process of sweating is vital for maintaining a core body temperature within normal ranges. When water losses are not adequately matched with fluid intake, dehydration occurs. Other than making us feel thirsty, dehydration leads to fatigue, increased perceived exertion, increased heart rate, stomach upset and impaired mental functioning. Fluid deficits as little as 2% of initial body weight (ie. 1.5kg for a 75kg athlete) have been linked to significant reductions in sporting performance.

Avoiding dehydration

When water losses are not adequately matched with fluid intake, dehydration occurs. No matter how hard you try, you can not train your body to handle dehydration. The best way to avoid dehydration is to commence your run session properly hydrated, then match fluid losses with adequate fluid intake. Everyone’s sweat rate is different, so determining your individual sweat rate will give the best estimate of how much you need to drink. See below for tips on determining your individual sweat rate. Remember sweat rates will vary according to temperature, humidity and intensity of the exercise, so it’s a good idea to carry out sweat rate testing under a variety of conditions.

Fluid intake during exercise is best tolerated when small amounts are taken at regular intervals. So remember small sips REGULARLY! Drinking volumes in excess of your sweat rate can be lead to stomach upsets and interfere with your performance. It is both unnecessary and potentially dangerous. So work out your sweat rate and stick to it!

Basic Sweat Rate Testing:

1. Weigh yourself before training (Initial Weight)
2. Weigh yourself after training (Final Weight)
3. Record how much fluid you drink during the session
4. Subtract Final Weight from Initial Weight.
5. The difference plus the volume of fluid consumed gives you your sweat rate for that period of time.
6. Divide this by the total time (hours) to determine hourly sweat rate.

Pre Cooling Strategies

There is emerging evidence for the use of pre cooling strategies to combat the debilitating effects of fatigue caused by heat stress and improve run performance in the heat. In the past athletes have used ice vests to provide external cooling to their bodies in a bid to prevent rises in body temperature, but more recently, the benefits of adopting internal cooling strategies like consuming cold (rather than room temperature) fluids and even ice slushies, have been found (Burke & Maughan, 2015).

So what should you drink whilst running?

• When running at a low intensity or for a short duration (<60min) plain water is fine
• When running in hot and humid conditions, chilled fluid before and during will be useful
• When running at a high intensity, for an extended amount of time (>60minutes) or in the heat, chilled sports drinks will be useful

Sports drinks are fluids that contain carbohydrate, electrolytes like sodium, potassium (some also include magnesium and calcium) and flavour. Sometimes they may also have vitamins, minerals and protein which are not always necessary.

Benefits of Sports drinks

• Convenient source of fluid, carbohydrate and electrolytes
• The presence of carbohydrate provides a readily available source of energy which has been linked to enhanced run performance
• The presence of electrolytes particularly sodium, helps replace electrolytes that are lost in sweat and assists with fluid absorption and retention
• The flavor, combined with sodium, stimulates the thirst mechanism leading to increased consumption of the fluid and maintenance of hydration whilst running

Rehydration

After running, replacing water plus electrolyte losses is crucial for optimal recovery. You continue to loose fluid through sweat and urine even after finishing your session, so aim to replace losses by 150%. In practice, this means if you weigh 1kg less after your session, you should drink 1.5L over the next 2-6 hours (1kg loss indicates 1L fluid deficit).

So what should you drink after running?

When questioned, most runners report water or sports drink as the best choices for rehydrating with after a long run. However new research looking at the hydration properties of various fluids supports what Sports Dietitians have been saying for a long time. As expected, researchers found oral rehydration solutions scored the best in terms of absorption and retention 2 hour post consumption, but to our great excitement (!), the research confirmed milk based drinks came out second best (Maughan, Watson, Cordery, Walsh, Oliver, Dolci, Rodrigeuz-Sanchez & Galloway, 2016).

So a milky drink, whether it be a homemade fruit smoothie or a purchased flavoured milk, remains my recovery drink of choice. Not only are these types of fluids well absorbed and retained by the body hours after they have been consumed, but they provide great amounts of protein to repair muscles and carbohydrate to replenish energy stores.

Final thought….

You dedicate hours to refining your running stride, spend a fortune on heart rate monitors and churn through countless pairs of runners to shave seconds off our times. So why neglect hydration? Everyone knows practice makes perfect, so getting into the right habits so you can train and race at your best, only seems so logical…doesn’t it?

To learn more about Katherine Shone visit http://www.opsmc.com.au/person/katherine-shone/

References

Burke, L. & Maughan, R.  (2015). The Governor has a sweet tooth – Mouth Sensing of nutrients to enhance sports performance, European Journal of Sports Science, 15:1, 29-40.

Maughan, R., Watson, P., Cordery, P., Walsh, N., Oliver, S., Dolci, A., Rodrigeuz-Sanchez, N. & Galloway, S. (2016). Randomized trial to assess the potential of different beverages affect hydration status: development of a beverage hydration index. The American Journal of Clinical Nutrition, 103: 717–23.