The good feeling of sitting in warm water has been known for centuries.   With the introduction of spas, 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 a man named James Crewk, who suffered from jaundice, palsy, rheumatism, and back pain.  Crewk was a drunk with a bad heart.  The records show that when he was immersed in warm water, the swelling in his legs was reduced and he excreted more fluid than he drank.

Oddly enough, there is not much documented on 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 of salt 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) was selected for the NASA experiments, because you weigh 10 percent of your body weight in water and that is as close as they could come to simulating weightlessness of space here on earth. Hormones triggered the electrolyte changes, they discovered, and NASA found a means to control hormones.  This work was helpful in finding out why soaking in hot water makes you feel so good.

Bodily Fluid Level - Within a half-hour, the blood had diluted by 20%. This means that the bodily fluid (plasma) level had increased by 20%. This additional fluid came from body tissue.

Stress – The stress hormones are adrenaline and non-adrenaline.  A high stress level produces more of these hormones, but the increase of plasma level brought about by soaking in warm water causes the hormones to become diluted and the rapid dilution of the stress hormones can lead to feeling less stressful.

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 to increase in diameter. The end result is that the blood can flow through your body more easily. The experiments showed that increasing temperature causes direct increase in blood flow. There is a 35% increase at about 91 degrees, a 60% increase at 95 degrees, and a 100% increase at 98.6 degrees. During this increasing flow, the pulse rate does not change. The heart is pumping more blood without having to work harder. 

So What Are the Advantages of Soaking?

1.  The loss of salts and minerals (electrolytes) may help kidney disorders, gout, hypertension and cirrhosis.

2.  The increase in bodily fluid (plasma) level helps remove inflammation from joints and helps heal muscle injuries and fractures. It also helps reduce stress by lowering hormone levels.

3.  Increasing blood flow without increasing hear 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.