01 Feb, 2011

Beat Your Thirst

Beat Your Thirst

November not only means first race of the season for most runners, it is also the month when we all realise that summer is here to stay! Excessive heat can certainly put us at risk and therefore staying hydrated is critical to our running performance – and more importantly, for preventing heat-related illnesses. Runners therefore need to pay attention to what and how much they’re drinking before, during and after exercise. – BY CHRISTINE PETERS

Dehydration in athletes can be very dangerous. It may lead to fatigue, decreased coordination and even muscle cramping. Other heat-related illnesses such as heat exhaustion and heatstroke have even more serious consequences. However, as runners we are not always sure of how much too drink.

At rest we need around 20-30ml of water per kilogram body weight, i.e. 4-5 glasses per day for a 55kg person or 8-12 glasses for a 95kg person. Pale coloured urine is an indication of good hydration, whereas dark coloured urine means you should consume more. However, be aware that excessive vitamin supplementation can offset urine colour.
During events, the best way to assess how much fluid you need is to know your own sweat rate. Use the following calculation to determine your individual fluid need per hour: body weight pre-run – body weight post-run. For example 50kg (pre-run) - 49.5kg (post run) = 0.5kg (500ml sweat).
Then calculate the above sweat loss (0.5kg) + fluid intake (0.5kg) = 1kg. Minus this (1kg) with urine output (0.3kg). This equals 0.7kg or 700ml. So your sweat rate is 0.7l/hr or 700ml/hr. This is what I should aim to drink per hour generally under the same environmental conditions.

• Do a light warm-up run to the point where perspiration is generated.
• Urinate if necessary.
• Weigh yourself naked on an accurate scale (remember to get dressed again before going out on
 your run!)
• Run for one hour at intensity similar to the targeted race pace.
• Drink a measured amount of a beverage of your choice during the run.
• Do not urinate during the run.
• Weigh yourself naked again on the same scale after the run.

You now know your approximate fluid needs per hour. Always take into account the different conditions and temperatures your event will take place in and factor more or less fluid accordingly. You should not have lost more than 0.5kg in body weight or 2% of body mass after an event or training session.

An endurance event can be defined as one that will challenge the athlete’s fuel and fluid reserves. Despite the best preparation possible, an athlete is likely to fatigue during an event from carbohydrate depletion as well as possible dehydration. Studies have repeatedly shown that during endurance events, especially those events longer than an hour, additional carbohydrate consumption can prevent, reduce or delay symptoms of fatigue and improve performance.

Remember, while exercising our muscles use carbohydrate (glycogen) as a fuel; once our muscle glycogen is used up we become fatigued. Our fully topped up muscle glycogen stores at the beginning of an event will only last us between 30-90min depending on the intensity that we are exercising. After this our bodies are dependant on the carbs we consume during the event.

Benefits of sports drinks include:
• Supplying working muscles with fuel (in the form of carbohydrate) and electrolytes.
• Preventing blood sugar levels from dropping low.
• Offsetting fatigue and muscle cramping.
• Improved hydration, because a diluted carbohydrate-electrolyte solution will actually achieve faster rehydration than water on its own. Sodium and glucose increase the rate of absorption of fluid into the blood from the gut. (This also helps offset nausea that is often felt when drinking too much water). An electrolyte solution also helps retain this fluid in the body instead of making you run to the toilet!

Type of carbohydrate: There should always be some High GI (quick-absorbing) carbs such as glucose, glucose polymers, dextrose, maltodextrins, maltose, corn syrup, glucose syrup, sucrose and oligosaccharides. A sports drink can contain small amounts of fructose (low GI) in combination with others already mentioned. Fructose in high concentration is best avoided due to risk of gastrointestinal upset.

Amount of carbohydrate (concentration): This is the amount of carbohydrate per 100ml (check the label). This should ideally be 5-10%, i.e. 5-10g of carbs per 100ml. In humid weather a solution of 4% is recommended and in colder weather 10%.

Electrolytes: Sports drinks should also contain sodium and, if taking diuretics, potassium. Sodium stimulates sugar and water uptake from the intestines and helps to maintain extracellular fluid volumes. Potassium levels lost in sweat can be a concern for people in general and especially for people taking diuretics for high blood pressure. Diuretics cause excessive excretion of potassium, and running could result in low potassium levels in the blood.

Osmolarity: This refers to the number of particles dissolved in the drink. There are hypotonic, isotonic and hypertonic drinks available. Blood osmolarity is around 300mOsmol/kg. Drinks with similar osmolarity to blood are called isotonic drinks and these are preferable if the demand for fluid and carbs is equally high such as with running marathons.

Runners should start all exercise sessions well hydrated. In the days leading up to your long run (or race), drink plenty of water and non-alcoholic fluids. Not only does alcohol dehydrate you, but it can also prevent you from getting a good night's sleep. It's not a good idea to run on a hangover because you'll most likely be dehydrated when you start running!

To ensure proper pre-exercise hydration, you should consume approximately 400-600ml of water or a sports drink. Sports drinks should now:
• Contain low GI carbs.
• Be low in fat (less than 25-30% of total KJ should come from fat)
• Protein should not be more than 15-20%.
• Carbs can be up to 20% concentration (20g per 100ml)
• Good pre-event sports drinks include Nestle Nutren Active, Ensure or Get- On-Up drink.

Keep in mind your sweat rate and fluid needs per hour. Drink 150-350ml approximately every 20min. Don’t wait too long before you start drinking. Remember in hotter weather you will sweat more. Sports drinks should now contain:
• Concentration of 5-10% (5-10g carbs per 100ml).
• Mostly Intermediate to high GI carbs.
• Sodium concentration should be 20-30mEq/L (Millie equivalents per litre).
• Good during-event sports drinks include Energade, Powerade or Game.

Post-exercise hydration should aim to correct any fluid loss during training or the event. Ideally consumed within two hours, your rehydration drink should contain water to restore hydration status, carbohydrates to replenish glycogen stores, and electrolytes to speed rehydration. The primary goal is the immediate return of physiologic function. You should drink 1-1.4l of water for every kilogram lost. If your urine is dark yellow after your run, you need to keep rehydrating. It should be a light lemonade color. Sports drinks should now contain:
• Intermediate to high GI carbs.
• Up to 20% carbohydrate concentration (20g per 100ml).
• Sodium concentration should be 20-30mEq/L (Millie equivalents per litre).
• Protein up to 20% of total KJ (protein helps improve muscle glycogen refuelling).
• Good post-event sports drinks include Powerade, Energade, Game with added PeptoPro or Cytopro Recovery drink.

1 cup of low-fat milk or yoghurt blended with a ripe banana (if preferred, add a little apple juice).

Hyponatremia, or low blood sodium levels, can occur if excessive fluid is taken in (more than lost in sweat and urine) or if low sodium drinks are consumed. Severe cases of hyponatremia may involve grand mal seizures, increased intracranial pressure, pulmonary edema, respiratory arrest, and in some rare cases even death. Risk factors for the development of hyponatremia include:
• Excessive drinking.
• Weight gain during exercise.
• Low body weight.
• Female sex.
• Slow running.
• Event inexperience.
• Non-steroidal anti-inflammatory agents.
• High availability of drinking fluids.
• More than four hours of exercise duration.
• Unusually hot conditions.
• Extreme cold conditions.

It is obvious that the ingestion of fluids and carbohydrate in sports drinks is beneficial, and athletes competing in endurance events should be encouraged to drink regularly. There is, however, a need to apply common sense. Working out your sweat rate and knowing what environments you are participating in will help figure out your fluid requirements. It is safe to say that runners should drink enough to limit weight-loss to not more than 2% of their body mass and that sports drinks should contain carbohydrate solutions between 5-10%, as well as electrolytes like sodium.