Tranquility, invigorating, refreshing… whatever term you choose, the undeniable pleasure of immersing ourselves in water is a conundrum. Why do we feel so serene and what exactly happens to our body as we sink down into aqua? Physiological changes occur although I doubt if we ponder what they are.
As we slip into the pool, water compresses our body. First, it forces blood into the deep vessels. When we continue to immerse, blood is pushed upwards into larger vessels of the pelvis and abdomen. As we slide deeper, blood travels above the diaphragm into the chest. When we’re up to our neck in liquid, about three-quarters of a quart of blood is displaced. Two-thirds of it goes into big pulmonary vessels while one-third accumulates in the heart.
Now that the heart has extra blood, it increases the amount moved with each beat, which is called stroke volume. If you’re up to your neck in water in a relaxed state, stroke volume usually increases approximately 30 percent. Cardiac output (total volume of blood induced by the heart in a minute) increases nearly 30 percent too. What exactly does that mean? The increase in volume and capacity at rest in neck-deep water equals about the same increase that occurs during light exercise on land.
Your body is smart and knows that more blood is circulating so the arterial blood vessels relax without increasing blood pressure. Healthy persons will lower their blood pressure and usually people with hypertension will benefit also.
Water temperature does make a difference. Often, blood pressure briefly increases upon entering hot or cold water. That’s why in the past, many health care professionals thought individuals with elevated blood pressure should avoid aquatic therapy.
But recently, several Israeli and Japanese studies concluded that people with mild to moderate heart failure benefited from aquatics: circulatory resistance decreases while heart contraction efficiency increases. One particular study compared the effects of water exercise with rest in patients experiencing moderate congestive heart failure. The group markedly improved aerobic fitness, muscle function, walking distance and exercise capacity. A 40 percent quality of life enhancement was an added bonus.
Why? One theory is that during immersion, more blood is pressed into deeper tissues causing improvement in muscle circulation and oxygen delivery. That expedites exercise recovery and muscle repair. Another study involving astronauts in training highlighted that blood flow into their calves increased almost 250 percent at rest while submerged in neck-deep H2O.
Immersion is also a boon to your kidneys with more blood entering them. But body radar in the heart and other areas sense that the additional blood volume is too much, so the body tells the endocrine system to slow down. The result is proper sodium and potassium excretion, increased urine volume, and somewhat more efficient kidneys. In fact, back in Roman and Greek times when medications were sparse, immersion was a treatment for kidney disease patients. As I stated last week, perhaps these societies realized the therapeutic benefits long, long ago. What happened between then and now?
Kay Sager is a certified fitness and aquatic specialist living at Port of the Islands. She is a personal trainer using land and water fitness and teaches swimming. She also has written articles for Physician and Sports Medicine among other publications. Kay can be reached by e-mail: firstname.lastname@example.org.