What Happens to Human Body in Water

What physiological changes occur when your body is immersed in warm water?

What happens to the circulatory system, the pulmonary system, and the muscle-skeletal system?

  • Cardiac output increases by 32% (at rest) during neck immersion.
  • The total work of breathing increases by 60%, expiratory reserve volumes decrease by 75% during neck immersion.
  • Muscle blood flow increases by 225% (at rest) during neck immersion.


Recent Articles and Research Shed Light on the Healing Effects of Water:

Although water is the oldest rehabilitation modality, few understand the magnitude, variety, and rapidity of its healing effects. Yet, much research over the centuries validates these effects, and recent research adds further understanding:

The aquatic environment produces physiologic changes that help remove metabolic waste, improve cardiac function, lower blood pressure, and aid the body in tissue healing.

How Water Therapy Helps Your Circulatory System

Immediately after a person is immersed, water begins to exert pressure on the body, with the following results:

  • Central venous pressure rises with immersion to the chest and increases until the body is completely immersed.
  • Cardiac volume increases by nearly one-third with immersion to the neck.

Since the ultimate purpose of the heart is to pump blood, its measure of performance is the amount of blood pumped per unit of time. This is called cardiac output.

Submersion in water to the neck depth increases cardiac output by 32% at rest. Therefore, the claim that water exercise is not aerobically efficient is faulty. In fact, it may be the ideal cardiovascular conditioning medium.

Your Pulmonary System will also Benefit from Aquatic Exercise

Like the circulatory system, the pulmonary system is profoundly affected by immersing the body to the thorax. This is partly due to blood shifting into the chest cavity, and partly due to compression of the chest wall. The combined effect of immersion:

  • Alters pulmonary function.
  • Increases the work of breathing.
  • Changes respiratory dynamics.

In fact, expiratory reserve volumes decrease by 75 percent at neck immersion, with vital capacity decreasing only slightly. These changes increase the total work of breathing by 60 percent.

A Regular Program of Water Exercise can Enhance Athletic Performance on Land

For an athlete accustomed to land-based exercise, water-based exercise is a significant workload challenge to the respiratory apparatus. With sufficient training time, this challenge can greatly improve the respiratory system’s efficiency.

Water Immersion Positively Affects the Muscle-Skeletal System

This is particularly true with vasoconstriction. On land, for instance, sympathetic vasoconstriction tightens the resistance vessels of the skeletal muscle to resist blood pooling. But in water, immersion pressure removes the biologic need for vasoconstriction, thus increasing muscle blood flow by 225 percent during neck immersion.

Aquatic Immersion also Creates Effects upon Renal Regulatory Systems

With increased water depth, the circulating central blood volume shifts, causing:

  • Flow of blood to the kidneys to increase immediately upon immersion
  • Increase in urine production
  • Increased sodium and potassium excretion

More on Healing Properties of Water