I was the Medical Director of the Mumbai Marathon, and during the 2011 race, I got a call that a runner had collapsed.

[the_ad id=”6152″] I dashed off to the spot, which was outside the Intercontinental Hotel on Marine Drive and saw the runner, lying sprawled on the road. He was semi-conscious and as I turned his head to assess him, I was shocked to recognize my good friend, Haresh (name changed). After a quick assessment, we transported him to our base camp and diagnosed it as a case of dehydration and rehydrated him with intravenous solutions.

Fast forward two years later, when Haresh took part in a sweat study- we found his sweat rate was at the high end of the spectrum, upwards of 2 litres per hour. This helped explain what happened on that Sunday in 2011, and I am sure he will now pay special attention to his hydration while exercising.

What is dehydration?

Dehydration is the lack of adequate body fluids for the body to carry on normal functions at an optimal level.  Dehydration occurs when the body loses more fluids than it takes in. Fluid deficits of more than 2% of body weight can compromise endurance exercise performance.

Dehydration can lead to:

• Muscle fatigue
• Loss of coordination
• Inability to regulate body temperature
• Heat illness (e.g., cramps, heat exhaustion, heat stroke)
• Decreased energy and athletic performance

How much do you need to drink?

The early guidelines recommended athletes drink as much as possible to ‘stay ahead of thirst’, but the newer guidelines have recommended using thirst as a signal to hydrate. In my opinion, given our weather conditions, it would be a good idea to have a hydration strategy beforehand and to stick to it during your run.

Two important factors should help you decide the amount you need to hydrate; your sweat rate and the ambient weather conditions. In a study, which I was a part of some years ago, we found that the sweat rates of Indian runners, ranged from 0.5-2.5 liters/hour. Think of the implications of this wide variance. A five-hour full marathoner, could then lose anywhere between 2.5-12.5 liters of fluid during the run! As you can see, there is a massive difference between the two, and therefore a one-size fit all strategy is not the best approach.  

Fluids before exercise:

Ideally, your body should be in a state of ‘euhydration’, before exercise, which is a perfect balance of fluid in your system, neither deficit or in excess. Sometimes, athletes tend to take excessive fluid before an event, which should be avoided, since it can lead to bloating.  It’s a good idea to consume about 500 ml of fluid, 2-3 hours before the event and another 250 ml, 15 minutes before the event.

Fluids during exercise:

An ideal plan is to drink sufficient fluids to replace sweat losses. As mentioned earlier the best way to do this is to calculate your sweat rate, which is described below. Do keep in mind that the sweat rate, will vary depending on the weather. I went through my running log, and noticed that the temperature on race day in Delhi in 2016, was 13.9* C, while a couple of months later in Mumbai, in January 2017, was 22.8* C. On both days, the relative humidity was about 77%. From a fluid replacement angle, the need would be greater in Mumbai, than in Delhi, all other factors being the same.

However, if you do not know your sweat rate, a good rule of thumb is to consume between 0.5 – 1 liter of fluid for every hour of exercise. You could split this amount into 4 parts, and drink every 15 minutes.

Do keep in mind that it is possible to consume too much fluid, and when this happens, the sodium content in your blood is diluted. Sodium is one of the essential electrolytes for life and its levels are tightly controlled within a narrow range. When the level in your blood falls below 135 mmol/l, it’s called ‘hyponatremia’. Symptoms usually occur, when the level falls below 130 mmol/l and these include, bloating, puffiness, weight gain, nausea, vomiting, seizures and loss of consciousness. Paradoxically, this is often seen in slower runners, who tend to mistake fatigue as a sign of dehydration and consume more fluid than needed. In our weather conditions, dehydration is far more common than hyperhydration and hyponatremia, but at the same time, it’s important to be aware that you could consume ‘too much fluid’ and it’s a potentially dangerous condition.

What should you drink?

For exercise lasting less than an hour, plain water is an effective fluid replacement. For exercise, lasting more than an hour, the body needs approximately 30-60 gm of carbohydrates per hour. This can be achieved by mixing it in your water, in a range of 6-8% carbohydrate concentration, or could be obtained separately too. It’s also essential to have a little sodium and potassium as part of your fluid replacement in longer runs, such as the half and full marathon. This fluid mixture could be obtained from a sports drink, or you could make your own sports drink, such as home-made ‘nimbu pani’, with sugar and a pinch of salt.

Fluids after exercise:

After prolonged exercise, most runners tend to be in a slightly dehydrated state, so it’s important to replace the fluids within two hours of exercise. Often sweat loss and urine loss continues in the recovery phase, so it’s advised to consume 1.25-1.5 liter of fluid for every liter of sweat lost (every kg of body weight lost immediately post-exercise).

Calculate your sweat rate:

• Weigh yourself in minimal clothing, at the start of your run. Ideally you should empty your bladder before weighing.
• Run for exactly an hour, at your usual pace, and do not consume any fluid during the run.
• Weigh yourself at the end of the run, in the same clothing again, ensuring you towel off any excess sweat from your body. Do not visit the washroom prior to your second weigh-in.
• Your weight loss indicates how much fluid you have lost. 1 kg of weight loss =1 liter of fluid lost.
• This number, in liters per hour, is your sweat rate.
• Do remember that the sweat rate is dependent on the weather conditions, and therefore for an ideal fuelling strategy, you should calculate your sweat rate under similar weather conditions of your race day.

The guidelines used have been taken from the latest American College of Sports Medicine (ACSM), position statement titled, ‘Nutrition and Athletic Performance’, published in the journal, Medicine & Science in Sports & Exercise.

 

Source:

Dr Aashish Contractor