200317 Fluid replacement-Water and the body-why we need it
In the book Essentials of Strength Training and Conditioning (page 247), it states that a fluid loss of around 1% of body weight will increase core temperature with a disproportionate rise in heart rate. These increases in temperature causes further fluid loss and the cycle repeats itself.
Plasma volume becomes reduced when sweating causes a fluid loss of 2-3% body mass. The blood thickens, which makes the heart work harder at pumping it through out the body. As dehydration progresses and plasma volume decreases, peripheral blood flow and sweating rate are reduced and thermo regulation becomes progressively more difficult. (Page 509 reference #1)
A 5% dehydration of the body mass significantly increases rectal temperature and decreases sweating rate. There is 25-30% decrease in stroke volume from the heart that is not off set by a higher heart rate so the system output and arterial blood pressure decline. For each liter of sweat loss, the heart rate increases by about eight beats per minute, with a corresponding decrease in cardiac output. “The primary aim of fluid replacement is to maintain plasma volume so that circulation and sweating progress at optimal levels”.
In Essentials of Strength and Conditioning, it (page 247) states that at 7% body weight loss a collapse is likely. Obviously, this is a serious condition if left unchecked.
Ultimately, the strain on the circulatory system impairs the thermo regulation of the body. (Page 507 reference #1)
Thirst is not a good indicator of hydration level as it normally lags behind the body’s needs. Each adult requires from 2-3 quarts of water/fluid daily, less than that, will gradually result in a dehydrated state over a period.
Indicators of the need for more fluid in the body that are relatively simple to monitor are (Page 247 reference #2)
- Dark yellow urine (unless excessive vitamin intake has occurred)
- Strong smelling urine
- Decrease times of having to urinate
- A rapid resting heart rate
- Muscle soreness that lingers longer than normal
Normal urine loss for an adult is about 4 times per day for a total of about 1.2 quarts. This means the elimination of 8-10 fluid ounces about 4 times per day. If a person is drinking over and above the normal requirements bathroom breaks could occur more often. If this is not the case, and you are not drinking excessively, perhaps a check for diabetes is in order.