I saw this post on Doc's site. For those of you who haven't read this here you go. It was written by Bob Lowry.
http://www.rhtubs.com/cgi-bin/bbs/config.pl?noframes;read=82853-----------------------------------------------------------------
Found this, interesting reading on this subject.
I wrote a paper some years ago about soaking and what happens in "hot" water. This combined with input from other source established some guidelines that were eventually adopted by the NSPI (now APSP).
Guidelines are:
104 degrees 15 minutes
102 degrees 30 minutes
100 degrees 1-2 hours
98 all day
The good feeling of sitting in warm water has been known for centuries. With the introduction of spas and hot tubs, Americans rediscovered that great feeling. But what makes it feel so good?
Two hundred years ago, a doctor in Bath, England, (of all places) recorded the effects of warm-water immersion on one James Crewk. Crewk suffered from dropsy, jaundice, palsy, rheumatism and back pain.
Dropsy today is called congestive heart failure, and fluid retention is common to this condition. Cirrhosis of the liver is associated with jaundice and back pain. In short, Crewk was a drunk with a bad heart. The records show that when he was immersed in warm water, the swelling in Crewk?s legs was reduced, and he excreted more fluid than he drank.
Oddly enough, there is not much documented medical or scientific literature to be found on warm-water immersion. However, in the early years of America?s manned space program, the National Aeronautics and Space Administration (NASA) became concerned about astronauts because of the illness and dizziness they suffered during relatively short periods in space.
A loss in salts and minerals (electrolytes) can cause this condition, and the agency realized that before longer space travel could be considered, a solution had to be found. Warm-water immersion (soaking in a spa or hot tub) was selected for the NASA experiments because you only weigh 10 percent of your body weight in water, and that was as dose as they could come to simulating the weightlessness of space here on earth.
The electrolyte changes, they discovered were triggered by hormones, and NASA has found a means to control hormones. But their work was helpful in finding out why we feel so good while soaking in warm water.
The experiments showed the following results:
Kidney function ? AL 95 degrees Fahrenheit, within a half hour, the kidney had put out twice as much urine as under normal, non-soaking conditions. At a temperature of 97 degrees F, the output of the kidneys dropped below normal. All of these changes are produced by hormones. The explanation is that the hormone responds first to the weightlessness but when the water temperature is higher than the skin temperature (about 95 degrees F), the process is reversed ? the body needs the electrolytes for sweating, so it saves them.
Bodily fluid level ? Within a half hour, the blood had diluted by 20 percent. This means that the bodily fluid (plasma) level had increased by 20 percent. This additional fluid came from body tissue.
Stress ? The stress hormones are adrenaline and noradrenalin. A high stress level produces more of these hormones. But the increase in plasma level brought about by the soaking caused the hormones to become diluted. And the rapid dilution of the stress hormones can lead to less stress.
Heart function ? There are bands of muscle surrounding the veins and arteries in your body. The effect of weightlessness is to relax these surrounding muscles, which allows the veins and arteries to increase in diameter. The end result is that blood can flow through your body more easily. The experiments showed that increasing temperature causes direct increase in blood flow, There is a 35-percent increase at about 91 degrees F, a 60-percent increase at 95 degrees F and a 100-percent increase at 98.6? F. During this increase in flow, the pulse rate does not change. The heart is pumping more blood without having to work any harder.
So, what are the advantages of soaking?
? The loss of salts and minerals (electrolytes) may help kidney disorders, gout, hypertension and cirrhosis.
? The increase in bodily fluid (plasma) level helps remove inflammation from joints and helps heal muscle injuries and fractures. II also helps reduce stress by lowering hormone levels.
? Increasing blood flow without increasing heart rate is less work for the heart, which may also help congestive heart failure. Muscle and tissue repair faster with increased blood flow. The body?s detoxifying system works faster with increased blood flow.
What about the flip side?
There are some disadvantages to soaking, but most of them are quite simple and can be avoided with common sense.
? Don?t drown. This includes keeping unsupervised children away and watching closely for hair entanglement.
? Sanitize regularly, and use other chemicals as directed to keep the spa or hot tub clean, sparkling and safe.
? Water temperature is important, Avoid prolonged exposure to water hotter than 100 degrees F. Never heat water to more than 104 degrees F
Understanding the physiology behind all this is one thing, but what makes soaking in hot water so enjoyable? My guess is that the millions of tiny bubbles breaking all over your body feels neat ? and that?s about as scientific as you really have to get.
