Staying well hydrated

Posted on 21/02/2012 by Ste Smith There have been 0 comments

Most runners have no clue as to how much water they lose during a run. In fact, very few sportspeople have any idea how much they sweat – and the effects that hydration (or lack of it) can have on their body. They might spend hours training their bodies to the peak of physical fitness, but without a clear understanding of the effects of hydration, how can they ever be expected to put in their best possible performance?


So why is hydration so important when it comes to running? Water acts as a coolant when you are exercising. Think of the water within your body as the anti-freeze you put in your car. Sweating is the involuntary response that keeps your body from overheating. When you begin exercising your body's temperature begins to rise, this in turn triggers your brain to signal your sweat glands to increase sweat production to speed up the cooling off process.

Because our bodies are comprised of 40-70% water, just a slight shift in the body's fluid balance can lead to drastic changes in our running performance. Sweating accounts for well over 90% loss in water during a run - add warm temperatures and humidity into the mix and this rate can go even higher. The remaining fluid loss comes from our breathing as well as urine and feces production. Keeping tabs on your hydration is essential to getting you through your run.

It has been reported that for every 1% drop in body weight from fluid loss, there is a 2% drop in your performance. This may not sound like a lot of weight, but for a 120-pound runner a weight loss of 3 1/2 pounds can lead to a 6% drop in running performance.

Finding your body water needs

With the worry that under-drinking can leave you dehydrated and suffering a loss of pace and over-drinking can have some nasty negative consequences such as nausea, dizziness and fatigue, it is sensible to work out your fluid replacement needs so that you can tweak your fuel plan to meet them.

Every individual is different so there is no one definitive answer that any one person can follow. However, there a couple of solutions. We can measure our sweat rate ourselves, for example. Follow the five-step plan below and easily calculate your own sweat rate.

Step 1: Weigh yourself (kg) in minimal clothing prior to running.

Step 2: Run at your ‘steady/natural’ pace for one hour.

Step 3: If you run and consume fluids, keep the bottle.

Step 4: Weigh yourself (kg) again in the same clothing as before and pat yourself down with a towel to remove surface fluids.

Step 5: The difference in weight is the amount lost in sweat during your run!

For example, if a runner weighs 75kg prior to setting off and does not drink any fluids while running but returns with a weight of 74kg after one hour, we can calculate that he or she lost 1kg of sweat which is the equivalent of 1 litre of fluid. This gives an approximate value of 1litre of fluids that should be taken on board while running every hour.

Of course, this is not exactly an instant process. It would be far better to get an instant result – something that the Tanita BC 1000 Body Composition Monitor is able to do quickly and efficiently. Tanita use Bio-electrical Impedance technology signals sent through the body to calculate how much water the body has; the theory is simple as water is very conductive whereas fat is not. This method is quick, simple and you will also get much more information such as muscle mass, body fat and basal metabolic rate readings. These measurements can be wirelessly downloaded to a PC and monitored over time to show how the body responds to intensive training and highlighting problem areas such as low body water, high body fat and irregular muscle development.

Simon Bradeley, Tanita’s Body Composition Expert says: “Keeping track of total body water on a daily basis is vital for athletes at any level, we know that if you are not properly hydrated before any race or training session you simply will not perform at your optimum capacity. We want all out athletes to get best results so we fit all Tanita Body Composition Monitors with Total Body Water as a basic feature.

“Understanding your body composition including body fat, muscle mass and total body water is important to maintain your motivation and ensuring safe and optimal training levels. At Tanita, we work with our Medical Advisory Board to ensure we are providing the most accurate data available to provide this information instantly in your own home.”

For each kilogram of weight lost, at least 1 litre of fluid should be added to your hydration protocol. In colder conditions (October can be a fickle month for weather) this will suffice, but when the weather is warm this should be increased to 1.2 litres per kilogram and in the extreme heat (80 degrees plus) 1.5 litres per kilogram.

As you get fitter your hydration needs may change, so it’s important to regularly monitor your body water levels and reassess your hydration needs every few weeks.

Hydration and training

Dehydration will make your workouts noticeably harder and put your health at risk, so don’t carry fluid deficits from one workout to the next. Again, checking your body water levels regularly will help you make informed decisions. You can make up for any previously incurred fluid deficits by consuming 400–600 ml of water or sports drink about 2–4 hours before your workout. If you are well hydrated, this should lead to urine production that is light in color (like the colour of lemonade). If it doesn’t, or if the urine that is produced is dark in color (like the colour of apple juice), drink another 300ml about two hours before you start pounding the pavement. Keep hydrating as needed prior to your training session, especially when conditions are hot or humid.

For training runs up to the half-marathon distance, your existing fuel stores should tide you over, and your focus can be on staying hydrated. Try to consume fluids at a rate that keeps pace with your sweat rate. However, your fluid needs can vary based on factors such as the intensity of your workouts and weather conditions. Clearly, the hotter it is, the more likely you are to sweat and in greater volumes. Staying hydrated in these conditions is obviously of greater importance and the performance losses will in turn be greater.

Factors that can determine our sweat rate include:

- Ambient or air temperature - the higher the temperature there is an increase in sweat production. But note that even in colder temperatures, the body will sweat, but at a much slower rate.

- Humidity levels - the higher the humidity, regardless of the ambient temperature, the more difficult it is for the sweat to evaporate off the skin making it harder for the cooling off process to take place. If you notice sweat rolling off your skin, this is an indication that you need to stay on top of your hydration.

- Wind speed- the higher the wind speed the greater cooling-off effect so that sweat production may be lessened. Calm days may lead to an increase in your sweat rate.

- Body conditioning - the better conditioned you are to a particular activity, the greater the sweat volume, so you will usually begin to sweat sooner into your run.

- Gender- men tend to sweat more than women, not only due to their bigger size, but also due to their increase in muscle mass.

- Genetics- we are all the product of our ancestral genes, therefore, some individuals sweat more profusely than others, even when not exercising.

- Wearing inadequate clothing: it is important to dress as though it is 20 degrees warmer than the actual ambient temperature. In other words, if the ambient temperature is 55 degrees, you will want to dress as though it is 75 degrees - usually this means shorts and a short sleeve wicking shirt. You may be a little chilled in the beginning of your run, but within a few minutes, as your body's core temperature begins to rise, so will your sweat rate.

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