The Science Behind the Soak

By Dr Bruce E. Becker
Thursday, 25 April, 2013

The Science Behind the Soak

What You Should be Sharing with Your Shoppers

Human beings have enjoyed warm water immersion since before written history. Many of our earliest habitation sites were established around natural hot springs, and the value of warm water immersion has been known since the earliest of times. Despite these facts, it is quite surprising that still today, we make so little use of the warm water environment in our daily lives, and use it so little for health advancement and preservation.

Over recent years, there has been a considerable amount of excellent research assessing the impact of warm water immersion and aquatic exercise on health. Immersion in warm water has been found to produce a quite dramatic impact upon the human autonomic nervous system, the component of our central nervous system that controls cardiovascular function, gastrointestinal function, blood flow and distribution, muscle tone and even a great deal of brain activity. 

The autonomic nervous system has two components: the sympathetic system and the parasympathetic system. The former creates what is commonly termed the "flight or fight" mechanism. It is evoked during fear and prepares our bodies for combat and stress but raising blood pressure and heart rate, increasing muscle tone, and facilitating intense brain focus on the causes of that fear, be it a rattlesnake or an enemy combatant. It is the part of the central nervous system that is in constant overload in post-traumatic stress disorder. The parasympathetic system becomes dominant during relaxed mood states, facilitating digestion, dropping heart rates and blood pressure, and allowing the brain to engage in a wide range of creative thought (refer to the diagram, Hypertension and Hot tubs). Warm water immersion causes a dramatic down regulation of the sympathetic system, allowing the two autonomic components to come into balance.

Research in our lab and by others has shown a very significant positive autonomic effect during warm water immersion in both young and older individuals. The effects that we saw, and that others have noted as well are parallel to the findings seen during meditation and after a period of quiet relaxation. Warm water immersion produces a reduction in anxiety. During this relaxed state, the brain is disengaged from momentary concerns and stresses. Memory functions improve, free-associative linkages are increased and this facilitates creative thought processes. It has always interested me that Winston Churchill daily took very long, very hot baths. They had to be kept at a particular temperature, measured by a thermometer. Sir Winston often dictated from the bathtub (his secretary would sit just outside the bathroom, portable typewriter on her lap) and he took meetings from there, as well. I’ve always believed that his creativity was due in part to the warm water immersion.

During warm water immersion typically heart rate and blood pressure drops, peripheral circulation improves, and the efficiency of the cardiovascular system improves (refer to the diagram on Cardiac Changes During Immersion). These effects have been translated into a number of studies of individuals with heart disease, showing that there is a significant benefit both with simple immersion and with aquatic exercise performed in a warm water environment for these populations. Cardiac function improves because the heart does not have to exert as much force to move blood through the circulation due to a reduction in vascular resistance and a slowing of the heart rate. As a result, in several studies assessing the impact of a period of 3-time-weekly aquatic warm water exercise, there was a lasting benefit. It is unfortunate that this is so poorly recognised within the health care industry, because if it were more widely recognised, our nation would likely see reduced health care costs and improved public health.

Another common public health issue that has been quite well researched is arthritis. For centuries, warm water immersion has been used for the management of both acute and chronic joint pain. During the last 50 years a number of studies have shown positive effects on both arthritic pain and function through warm water aquatic exercise, while the benefits of simple static warm water immersion have received less attention. Because immersion produces hydrostatic pressure upon the body, there is a driving force to decrease joint swelling, both in acute arthritis as well as in post-operative joints, particularly in knees, ankles and even hips. This can facilitate pain reduction and increase joint movement. Immersion produces buoyancy, offloading joints and further reducing pain and allowing strengthening activities, which can improve activities of daily living, balance and coordination, and endurance. As a consequence of these combined benefits, many studies of individuals with arthritis show quite sustained improvements in pain levels, gains in functional abilities, and improvements in mood and self-confidence. 

While not a joint-specific problem, fibromyalgia is categorised within the constellation of arthritic diseases. The actual cause of fibromyalgia remains unknown, and medical treatment is problematic with the available drug therapies having significant side effects, leaving fibromyalgia patients with quite limited options. A substantial number of studies have shown the benefits of warm water exercise and even simple immersion on muscle pain, strength, endurance, and overall health-related quality of life in individuals with fibromyalgia. It is quite safe to say that no other medical intervention currently available for fibromyalgia offers such substantial benefits with so few side effects or such little risk. 

Of course immersion in water of almost any temperature produces buoyancy, offloading joints, reducing the load upon the spine and intervertebral discs, increasing peripheral circulation and reducing heart rate. The unique effects of warm water are to add to the feeling of relaxation and well-being, with a typical reduction in pain if present, and a further significant decrease in blood pressure. These effects can be beneficial in healthy people, and very beneficial in a number of health issues, including heart disease, arthritis, anxiety disorders and depression. 

While these effects have been recognised since almost pre-history, it is certainly surprising that they have been so little established within our contemporary society, within general medical practice, and within research funding opportunities. It is far easier to find federal funding for complex medical technology than for aquatic health benefits, unfortunately both for general public health and for the economic value of the industry. While there is emerging understanding of the value of warm water immersion, the level of public recognition remains low. As an industry, we need to work aggressively to improve public awareness, by using science, the media and by our actions. We can create a better future for all. 

This article is reprinted with permission by Pool & Spa Marketing, Canada’s national trade magazine for the swimming pool, spa/hot tub, and landscaping industries. This article originally appeared in the June 2012 issue. To review this issue in its entirety, visit or for more information on the magazine, visit .

About Dr Bruce E. Becker

Dr Bruce E. Becker is an internationally recognised expert in the field of aquatic therapy. He is the editor and co-author of Comprehensive Aquatic Therapy, now in its 3rd edition and has written, researched and lectured extensively in the field of aquatic therapy over the past 30 years. Dr. Becker also serves as the Director of Aquatic Health Benefit Research at the National Swimming Pool Foundation (in the USA). He is a frequent presenter at the World Aquatic Health Conference, his seminars can be viewed online at

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