S.W.E.A.T – Why know your Sweat Rate?
Posted On 17 Apr 2012
Why know your sweat rate?
When I started undertaking the ‘Sweat Rate’ study, there were many readings that I came across that I want to share. I am putting certain key points as bullets here.
- There are couple of ways of hydrating yourself when you run. One is called ‘ad libitum’, which means drink as you feel like. Another one is drinking by some ‘predicted’ sweat loss numbers and Thirdly by working from your own ‘Sweat Rate’. Almost all of us have been following the first method. Nothing wrong with that. I, myself have done this for all my Half Marathons. I have improved my timings, run Half Marathons all through the year and nothing has happened. But considerable research indicates that things could be better for me if I knew my ‘sweat rate’ and ingested fluids based on it.
- In a Nevada Desert Study ( Noakes 1993 ) groups of soldiers were required to march across the desert and the findings noted was, “Even when given free access to adequate fluids, subjects drank less than they lost in sweat and urine. Hence they developed voluntary dehydration that was corrected only after exercise was completed and food was eaten..”
- Subjects stopped exercise when they reached 7% to 10% of dehydration, higher levels of dehydration resulted in organ failure, particularly kidneys ( understandable ) and for every 1% of dehydration the core temperature increased between 0.2% to 0.3%
- Other studies have established that dehydration raises the heart rate and body temperature during exercise, reduces the heart’s output and stroke volume, as well as blood flow to the skin, and the exercising muscles., all in proportion to the degree of dehydration. Most of also know that an increased HR results in an enhanced perception of effort resulting in earlier onset of fatigue.
- Even more important is the finding that the rate of sweat loss does not fall down with increased level of dehydration. In short even if you are dehydrated, your body does not adjust sweat rate levels downwards. You keep on sweating at the same rate till the point of fatigue.
- While the effects of dehydration is understandable, over ingestion of fluids is also not desirable for 3 reasons
- Overdrinking of fluids results in a condition known as hyponatremia ( dilution of body salts levels such that it impairs performance )
- Gastrointestinal distress from having too much fluids sloshing around
- The increased effort of having to run with that extra weight on you
So the bottom line is not to drink too les, and not to drink too much either. Be within range of your own ‘sweat rate’….which is why you must take advantage of the study.
My next post on this will elucidate the Position Stand of the American College of Sports Medicine ( ACSM ) the worldwide authority in matters relating to sports and physiology.
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