Proof: What Science Knows About Aquatic Exercise

Bruce Becker Head Web

The basic fact that aquatic activity can provide important health benefits is not new. What few people realize, however, is just how pervasive and multi-faceted those benefits really are, and how pools and spas are truly health and fitness products. Here, Dr. Bruce Becker, one of the leading researchers on the topic and longtime advocate of aquatic therapy and exercise delves into a number of specific areas where getting wet can improve overall health.

Over the past 10 years or so, public awareness of the health benefits of water-based activities has grown. Unfortunately, the magnitude of those benefits is not common knowledge and very rarely covered in the lay press. As a result, the scope and utility of those benefits remains largely unknown to the public. As someone professionally devoted to advancing the science behind the amazing effects of aquatic activity, I find the status quo enormously frustrating.

From a research standpoint, the study of immersion and the benefits of aquatic exercise remains incredibly exciting. There’s a growing body of scientific understanding of the subject, and as the research community uncovers more and more empirical evidence of the benefits, we become aware of new areas of inquiry that will very likely make the case even stronger. Unfortunately, there remains a significant deficit in research assessing the effects of aquatic activity upon specific health issues, and this in turn creates a lack of understanding of potential benefits among many in the medical profession.

In terms of acceptance and application of this growing body of knowledge, we have seen progress within some sectors of the health care community. For example, most physical therapists these days have come to recognize the range of ailments that can be addressed through aquatic exercise programs, which is extremely encouraging. Many physical therapy clinics now make use of aquatics, which is a recent and positive development.

These days, medical awareness really does depend on whom you talk to. Many orthopedists do seem to understand the multiple benefits of aquatic therapy in treating their population of patients. However, I don’t find the same awareness when talking to cardiologists, because the impact of water exercise on heart health hasn’t received as much publicity and recognition. The same thing is true of pulmonologists who have not gained awareness of the ways that aquatics can be used to benefit patients with respiratory problems.


Part of the problem is that there are clinical areas that we still need to address, a few of which I’ll discuss below. Ahead of that, there needs to be far more discussion about what we already know that has been confirmed by research.

Certainly, the pool and spa industry and other related aquatics industries can do much more in first understanding the tremendous power of both immersion and aquatic exercise and then championing that information when talking to the general public. In my view, these benefits should become common knowledge among all water professionals because they are fantastic selling points for the entire aquatic industry.

Right now, we’re in a time when not only are communities failing to build new aquatic facilities, but in many places they are closing existing pools. That is a horrible trend for the pool and spa industry. It is clear evidence that as a society, we do not properly value the vast spectrum of health benefits associated with aquatic activity. When communities fail to provide places for the public to use and enjoy the water for recreational purposes or for therapeutic uses our society and its health are the poorer for it.

Part of the challenge in making our case boils down to fostering a fundamental understanding of exactly how it is that water makes such a difference when compared to dry-land exercise and therapy. That understanding begins with the physiological effects of immersion and the physical properties of water that produce beneficial biological effects.


The first property to consider is water’s density, which is the simple measurement of mass per unit volume. Water is denser than the human body, so when you’re immersed, it counteracts the force of gravity. Density therefore relates directly to buoyancy. Because water is denser than your body, the more you immerse into it, the more hydrostatic pressure is created, which relieves the effect of gravity. In lay terms, you weigh less when you’re in water.

Relieving gravity is probably the most well-known benefit in that it “off-loads” joints, which is why exercising in water is good for folks with hip or knee replacements and people with arthritis or back problems. That’s a huge benefit by itself, but there are other things that happen as a result of simply sitting or reclining in water.

Because water is denser than your body, it exerts hydrostatic pressure on the skin surface and underlying blood vessels. That moves blood up into the chest cavity, which in turn creates a reaction in the cardio-vascular regulatory system, causing blood vessels to relax. That means in an immersion environment, the heart muscle faces less resistance from the circulatory system, making each systolic contraction of the heart more efficient in terms of moving blood. That effect is enhanced because hydrostatic pressure has moved more blood into the chest cavity, increasing what is known as the intrathoracic blood volume and enabling the heart to fill with a greater volume of blood during its relaxed phase.

Keep in mind the heart only has two ways of increasing blood flow: It either increases heart rate or it pumps more blood per contraction. Research has demonstrated that increasing blood flow by way of increased volume per systolic contraction is more energy-efficient than by increasing the heart rate. (This is much like the increased efficiency you can realize in a hydraulic system by increasing pipe size.)

Viscosity is another property of water that has significant physiological impact.

In my work with elite track athletes, we tried having them do the same workout in water that they were doing on land. What happened as a result was almost magical. After high-intensity training in water for a period of time, many would return to the track and find that they had actually improved their personal times — often significantly so.

One reason for that improved performance: the work of breathing is increased when immersed. Because of the increase in blood volume in the chest cavity and hydrostatic pressure on the chest wall, the work of breathing is increased about 60 percent even at rest. As you increase the respiratory rate in a workout, you increase the rate at which you have to push blood out of the chest cavity and replace it with air, and you also encounter viscosity by expanding your chest cavity against the resistance of water. Given a 60 percent increase in respiratory workload at rest, this workload must be substantially greater at high respiratory rates. This increased workload likely can both strengthen and build endurance in the muscles of breathing.

The thermal properties of water also play a significant role. Water has substantially higher conductivity than the human body, so it is either constantly moving heat to or from the body. It is four times as conductive compared to the human body and 25 times more conductive than air.

This is why you can sit in a room at 72 degrees and feel no sensation of hot or cold, but if you jump in 72-degree water it feels quite cold. Because of water’s high conductivity we are able to increase or decrease blood flow to a particular part of the body for therapeutic purposes. (A familiar example would be baseball pitchers who soak their arms in ice water after pitching to reduce swelling and inflammation.)


Those physical properties of water work in a wide variety of ways that benefit numerous systems within the body. In many cases, there is definitive research that supports our understanding of these benefits. In many others, I and other physicians and researchers suspect a number of additional positive effects that have yet to be studied.

Starting with the heart, we know with an extremely high degree of certainty that immersion in neutral or warm water lowers blood pressure. We suspect the effect of lowered blood pressure persists for a period of time after immersion or aquatic exercise. Exactly how long has never been studied. As mentioned above, we also know immersion increases cardiac volume and output while decreasing vascular resistance.

There are some beautifully done studies of patients with varying levels of mild to moderate heart failure who use aquatic exercise and quite consistently, they dramatically improve.

The benefits to the respiratory system are also tremendous. On the most fundamental level, working out in water strengthens muscles that drive respiration. This is what we found through our experience with athletes working out in water who then saw improvements in their performance on land.

When you become fatigued during vigorous exercise, the brain sends out a signal that causes what is known as a metabo-reflex. This reflex acts to constrict blood flow to the extremities, making more blood available to the respiratory muscles. It’s a type of survival mechanism. When this happens, blood flow to your arms and legs and other parts of your body that aren’t as critical for survival as your respiratory muscles decreases. This is, in part, why when you fatigue, you slow down and feel weaker. I believe that when you strengthen the respiratory muscles in water, you delay fatigue and forestall that metabo-reflex effect. There’s a great deal of anecdotal evidence to support that hypothesis, but there has yet to be a specific study on the subject.

Probably the most accepted and well-known benefits involve muscles and bones. As previously mentioned, buoyancy of the human body relieves stress on bones and joints, and we also know that aquatic exercise increases muscle blood flow. This is a big part of why people with chronic orthopedic conditions or post-operative conditions benefit from exercising in water.

Beyond that, there is reason to suspect that immersion and aquatic exercise increase bone blood flow, which could have major implications in bone healing. Again, on an anecdotal basis, I’ve seen many instances where athletes with stress fracture injuries (a common overtraining injury in track athletes) become asymptomatic very quickly as they exercise in water.

I also suspect that there’s an increase in synovial fluid production in the joints. Every joint is dependent on cartilage, which is protected by the synovial membrane, which produces synovial fluid, which acts as a lubricant for the joint. I believe this is one of the reasons that arthritic patients improve when they perform water-based exercise.

The kidneys benefit from aquatic exercise, as well. Aquatic activity triggers a complex set of responses that ultimately increases renal blood flow and alters renal hormones, which in turn increases renal efficiency by way of promoting sodium excretion and increased diuresis. That’s why urine production increases while in water. In short, aquatic exercise makes your kidneys function more efficiently.

Finally, there are benefits to the neurological system in the form of increased flow of blood to the brain and the promotion of relaxation and the reduction of pain sensations. We also have reason to believe that aquatic exercise improves balance and sleep patterns, both of which also require more study.


Even when surveying this truncated list of benefits, both proven and suspected, it’s abundantly clear that water-based therapy and exercise should be embraced at all levels of society. I believe it’s an indisputable fact that these activities can improve the quality of life for everyone from Olympic athletes to people stricken with a range of chronic conditions or severe injuries.

Yes, there needs to be much more research on a variety of fronts, but we already know quite enough to more than justify placing a far greater value on this genre of activity. And now, with the aging baby boomer generation moving into retirement and with rising health care costs, this is an area that should be at the forefront of our collective mindset. Our society faces huge challenges where health and aging are concerned, and here we have a tool that can make an enormous difference, that is largely going unnoticed.

I urge everyone in the pool, spa and aquatics industry to consider the power embodied in your products and find ways to promote awareness of this information.

If there’s ever been a win-win situation, this is it!

Comments or thoughts on this article? Please e-mail [email protected].

China Globe Web

Awareness Abroad

There does seem to be an increasing awareness of the benefits of immersion and aquatic therapy outside of the United States. As an example, China’s government is in the process of building a large number of rehabilitation hospitals over the next several years, all of which are planned to include aquatic therapy facilities. They are making a huge investment on this front and they intend to include aquatic therapy as one of the primary avenues of treatment across a range of injuries, illnesses and conditions. I know this because I was recently approached by Chinese officials who are interested in building awareness about aquatic therapy benefits and developing treatment regimens for their aging population. That’s extremely encouraging, but I certainly would love to see that kind of forward motion here at home.

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