image credit: http://www.jccns.org/

image credit: http://www.jccns.org/

I suspect many you are like me: there is something dramatically wrong with your body and it has been that way for quite a while.  You surf the ups and downs of your symptoms and occasionally wonder, “What does this symptomatic change mean?”

If you are like me, you have learned that most medical doctors are not much help, and even if they are interested in helping you, they are too harried to spend any extra time investigating your odd collection of symptoms.  So eventually we find that our best resources default to learning from other patients and keeping up on the latest research that might be applicable to providing some relief, if not a cure.

About three months ago I was doing my usual hunting and pecking around the Internet in a search to better understand the interplay of two long-standing symptoms of mine that had driven me to despair: myofascial pain/trigger points and allodynia. I found a patients’ website for CRPS (Complex Regional Pain Syndrome) where the author strongly suggested that allodynia sufferers try sitting in a neutral temperature therapy pool.  “Try it; it will reduce your allodynia”, she wrote. (I wish I could find that website again so I could attribute and thank her, but, alas, no luck.)


“Try it” she said “It will reduce your allodynia”

So I went and sat in a neutral temperature therapy pool for 10 minutes (start low, go slow) and there was a tiny shift in my allodynia and myofascial pain symptoms that faded away after a day or so. That was 4 months ago.  I have continued twice a week since then and I am up to 30-35 minutes a soak resulting in a small and somewhat temporary, but noticeable, lessening of allodynia and myofascial pain.

In the 20 years of having these miserable symptoms, I have never had any success with anything I have tried, so I was curious about what was happening. I asked numerous medical practitioners if they knew why sitting on my butt in neutral temperature water would help produce this shift in my symptoms.

None of them knew — I will refrain from my desire to make some cynical comments here — so I went out and wrangled myself up a huge digital stack of research papers on human physiology and water immersion.

The Science

Health practitioners usually recommend people with chronic illnesses use a “neutral temperature” therapy pool because it will induce the least stress.

Pressure from the, er, water increases your heart rate and blood flow

Pressure from the water increases your heart rate and blood flow

The temperature of a neutral temperature pool is near the human body’s internal temperature, which is a good temperature for people who will largely be inactive within the pool. The Aquatic Physical Therapy Section of the American Physical Therapy Association has a general recommendation of 92 to 96°F for the inactive patients and 88 to 92°for arthritic patients.

The pool I go to is 92°, which is my normal skin temperature.  Some days, when I get in the water, it feels a little cool and some days it feels a little warm. This pool is the only choice I have, and I feel lucky to have access to this inexpensive community therapy pool.

The hydrostatic pressure of water in a pool will compress the immersed part of your body (similar to how compression stockings compress your legs). The water will also push your body upward. Interestingly for people with ME/CFS the increased hydrostatic pressure also results in a pretty dramatic rise in the central blood volume (in the thorax region). Blood volume and stroke volume in the human heart also dramatically increase.

How much of an increase depends on how deep you are immersed, whether you are sitting, standing, or doing a back float, the water temperature, and your activity level. The increased blood volume and the upward displacement of the abdomen contents and diaphragm in the thorax cavity makes it much harder for your lungs to work and for you to breathe. That causes your heart to compensate by working harder. Come to think of it, this sounds similar to what happens when we exercise!

Credit: http://aquatic.transitionsrehabilitation.com/

Credit: http://aquatic.transitionsrehabilitation.com/

When you are in the pool, your heart is pumping harder and expands with more blood. That causes your blood to circulate faster with increased volume towards your peripheral limbs and head.

About a quarter of your heart’s output goes through your kidneys, which results in more changes.  When the cardiopulmonary stretch baroreceptors detect increased blood volume in the thorax, they decrease your kidneys’ sympathetic activity.

This results in increased urine excretion (you want to pee much faster.) The sources I used quoted a sevenfold increase in urine excretion. I come from a family of almost fishlike siblings.  We really liked the water.  Keeping with my curious nature, I used to wonder why I would have to stop swimming to take a pee when I never was drinking any water.  Now I know

Two other renal related physiological changes occur with water immersion: increased natriuresis (sodium excretion in the urine) and paturesiss (potassium excretion).  These two processes lower the amount of sodium and potassium in your blood. This is not a good thing if you have POTS (Postural Orthostatic Tachycardia Syndrome) and are taking blood volume enhancers that have already lowered sodium or potassium levels.

It does explain, however, why, after coming home from a 20 or 30-minute soak in the therapy pool, I’d often feel exhausted and fall asleep for a couple hours.  Nowadays I take a quart of water with some potassium and sodium salts and other electrolytes with me and drink it after the soak.

About Me

At this point, let us take a break and let me give you a little personal information.  I fall into the patient subgroup of ME/CFS with co-morbid fibromyalgia, POTS, and CRPS/RSD-like neuropathic pain (allodynia). I have been walking around feeling like I have blocks of ice on my feet for years.

Some time ago, before I knew about POTS, vasodilation, or vasoconstriction, I was grousing to myself about my cold feet and ankles.  I looked on my coffee table and saw a thermal infrared gun I was using to detect insulation leaks in my house. It’s a cool little device: you just point it at something and it tells you the surface temperature of the object.


Ten minutes later Tim’s feet were at a normal temperature for the first time in years

So I took off my socks and pointed the thing at my feet and then at my thigh. My thigh was 92°F and my feet were 72°F. I’d noticed when I first entered the therapy pool that my feet felt cold, while the rest of my body did not feel much thermal change. The rest of the day, though, I would not have much problem with cold ankles.

So I took my trusty thermal infrared gun to the therapy pool and zapped my feet before entering and at my feet after a half an hour in the pool.  My feet were 72°F before entering and 92°F after exiting. Why?

Peripheral vasodilation and autonomic balancing

Now comes some good news about water immersion.  I thought that the increased cardiac stroke volume and output should result in an increase in blood pressure.  Instead, your body detects that increased cardiac output and causes peripheral vasodilation (areas peripheral to the thorax cavity have vasodilation increase) to accommodate the increased cardiac output.

Pool immersion also tends to balance out the autonomic nervous system

Pool immersion also tends to balance out your autonomic nervous system

The means more blood flows to your tissues, and, in my case,no more cold feet. Water immersion also affects the autonomic nervous system.  The autonomic nervous system is a control mechanism for the systems in our body that we don’t consciously control: the cardiovascular system, the gut, thermoregulation, etc.

Heart rate variability analyses of water immersion have associated it with decreased sympathetic influence and a “balancing” of the autonomic nervous system.

It appears that thermo neutral water immersion pushes the autonomic system towards being back in balance.  This is a very good thing for the many people with chronic and/or autoimmune diseases that feature sympathetic arousal, such as fibromyalgia, ME/CFS, POTS, CRPS, and multiple sclerosis.

Reduced myofascial pain and allodynia

I still wondered why thermoneutral water immersion seems to temporarily reduce my myofascial pain symptoms of excruciatingly painful trigger points, and taut, ropey muscles (ugh!).  I could find nothing mentioning muscles in my research until I came across a paper by Petrofsky, et.al. on hydrotherapy and the cardiovascular system and muscle relaxation.

Credit: Petrofsky, et.al. “The Influence of Warm Water Hydrotherapy on the Cardiovascular System and Muscle Relaxation"

Credit: Petrofsky, et.al. “The Influence of Warm Water Hydrotherapy on the Cardiovascular System and Muscle Relaxation”

In this study they took 10 healthy 20 to 30-year-old students and immersed them in 96.8°F (37°centigrade) water for 30 minutes.  These brave (or is it naïve?) students endured a slew of probes, insertions and adhesive patches to measure the myriad of functions including heart rate, blood volume, blood flow to the muscles and skin, and muscle temperature and stiffness.

The results were enlightening.  They found that the limb muscle temperature increased from 31°C at the beginning of water immersion to 36°C after 12 minutes and stayed at that temperature for the rest of the immersion period.  Both muscle and skin blood flow increased, with muscle blood flow increasing faster and more dramatically. Within 20 minutes of immersion the blood flow in the muscle increased 300% (!) and then stayed at that level for the rest of the immersion period.  The skin blood flow continued to rise throughout the 30 minute immersion, finally leveling off at a 200% increase.

They also found significant relaxation in the muscles and reduction in the activity of associated alpha motor neurons. These authors speculated that a 6°C increase in muscle temperature would conservatively result in doubling or tripling the muscle metabolism.

They also found that the heart stroke volume, heart rate, and cardiac output was significantly higher, but no significant difference in blood pressure was seen from the beginning to the end of immersion. This implied vasodilation was taking place in the rest of the body.

Credit: Petrofsky, et.al. “The Influence of Warm Water Hydrotherapy on the Cardiovascular System and Muscle Relaxation"

Credit: Petrofsky, et.al. “The Influence of Warm Water Hydrotherapy on the Cardiovascular System and Muscle Relaxation”

Interestingly, they also tested the subjects while exercising lightly in the immersion pool, and then outside of the pool on a stationary bicycle. Skin and muscle blood flow and muscle relaxation were significantly greater in the subjects when they were immersed in the thermoneutral water and not exercising.

In fact, stationary bicycling without immersion had no significant effect at all on skin blood flow at all.  The authors concluded that if muscle relaxation is the goal of water immersion therapy, then exercise in the pool should not be attempted.

So what does all this mean?  My guess is that passive immersion in thermoneutral water results in peripheral vasodilation and increased blood flow everywhere, including the muscles, which in some ways mimics exercise — but without the added oxidative stress, lactic acid, and other detrimental effects that cause the delayed muscle pain and malaise familiar to many of us patients.


However it works it helped; neutral temperature pool immersion was the first thing to help Tim’s allodynia for decades

What about allodynia?  One of my previous posts on Cort’s website indicated that McGill University (a leading pain research institution) researchers found that microcirculation issues resulting in ischemia contributed to allodynia.

Perhaps, the increase in blood flow to the peripheral muscles and skin while in the immersion pool results in reduced ischemia and allodynia. It’s also possible that, as some authors speculate, when your body is immersed in water the nociceptors that sense touch and temperature are bombarded with signals and block out the allodynia. My bet is on the increased blood flow.


Knowing the science of thermoneutral water immersion will keep me trudging down to my community center pool, paying a few dollars, and sitting in water the same temperature as my skin. While I’m there I’ll contemplate how after almost 20 years of poking, prodding, tilting, and jolting (ever have a nerve conduction test? no fun) in addition to enduring countless pharmaceutical side effects without any positive symptomatic effects while spending a significant amount of money within a broken healthcare system, something so simple as sitting in warm water has backed me off of the edge of despair.

The coolest part about it?  It is pleasant and enjoyable.

Dog Onsen (Japanese traditional natural spring baths). Credit: http://www.shifteast.com

Dog Onsen (Japanese traditional natural spring baths). Credit: http://www.shifteast.com

Addendum: If you’re going to try thermoneutral water immersion, I highly recommend you follow the old slogan of “start low and go slow” and rehydrate with electrolytic fluids.

I have experienced some dramatically negative effects when I overdid activities or duration time in the pool, or did not rehydrate.

Healthcare practitioners kept encouraging me to do more active stretching and more muscular exertion, but every time I took their advice I had some dramatic crashes afterwards. Go slow, and pay attention to your body’s response. Everybody’s body is different and you know your body better than anyone else.  For my body, less is more.

Additional Reading:  THE INFLUENCE OF WARM HYDROTHERAPY ON THE CARDIOVASCULAR SYSTEM AND MUSCLE RELAXATION. Jerrold Petrofsky, Ph.D., JD  Jaime Baxter, BS  Jaime Bomgaars, BS  Carrie Burgert, BS  Sara Jacobs, BS  Danielle Lyden, BS  Everett B. Lohman III, DPTSc, OSC.

Hydrotherapy for the Treatment of Pain in People with Multiple Sclerosis: A Randomized Controlled Trial. Adelaida Marıa Castro-Sanchez, Guillermo A. Mataran-Penarrocha, et. al., Evidence-Based Complementary and Alternative Medicine, Volume 2012, Article ID 473963.

Rehabilitation Medicine Improvement in Anxiety and Pain After Whole Body Whirlpool Hydrotherapy Among Patients With Myofascial Pain Syndrome. Ann Rehabil Med 2013;37.  Sang Hee Im, MD, Eun Young Han.

Biophysiologic Effects of Warm Water Immersion. Bruce E. Becker, Kasee Hildenbrand, Rebekah K. Whitcomb, and James P. Sanders. International Journal of Aquatic Research and Education, 2009, 24-37  ©2009 Human Kinetics, Inc.

Age-Dependent Autonomic Changes Following Immersion in Cool, Neutral, and Warm Water Temperatures. Kasee Hildenbrand, Bruce E. Becker, Rebekah Whitcomb, and James P. Sanders. International Journal of Aquatic Research and Education, 2010, 127-146 ©2010 Human Kinetics, Inc. Al Haddad, H., et al.,

Effect of cold or thermoneutral water immersion on post-exercise heart rate recovery and heart rate variability indices, Auton. Neurosci. (2010), doi:10.1016/j.autneu.2010.03.017

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