I have said elsewhere that your body moves differently in the water, and it’s true. Even experienced athletes and Olympic swimmers have to make adjustments to accommodate water’s effect on the body.
Viscosity, Density and Resistance
Water is more dense than other mediums like air we are used to moving in. We can move through air from one place to another pretty quickly because the molecules in air are not packed very closely, which is the same thing as saying air is not very dense.
It’s harder to move through water from one place to another because water molecules are packed together more closely than air molecules. Water is denser than air; 800 times more dense to be more exact. (Salt water is even denser than other water, which makes it great for floating but more of a challenge for moving and swimming.)
Because water is denser than air, moving through it takes more effort than moving through air. The challenge you notice means you are getting resistance from the water. You are actually pushing the water out of the way every time you move, even if you are walking. Your muscles are moving against resistance, the same thing they do when you do resistance or strength training. People (and their muscles) generally aren’t used to getting this kind of resistance when they move, which is the primary reason I recommend newcomers to Aqua Zumba start out in a gentle class, even if they have strong muscles and exercise a lot. (There are other reasons your muscles don’t operate the way you expect in water, but I’m saving that for a different post.)
BUoYANCY
Another property of water that makes Aqua Zumba a little different than other types of exercise is the buoyancy factor. As I said above, water is more dense than air. Water is also a lot more dense than human bodies. If one object is more dense than the medium it is on or in (like air, water, mud, or oil), the more dense medium will push the less dense object up, which is referred to as the buoyance factor. Helium balloons float on air because the helium inside the balloon is less dense than the nitrogen/oxygen mix of air. Because they weigh less than the air, the air pushes them upward. Similarly, most human bodies are less dense than water. If you let yourself relax completely, the water will push you up to the point where you are floating on top of the water. The exception to this is people with a lot of muscles. Muscles are more dense than air, so people with very muscular bodies might not be able to float.
How much you float depends to some extent on how much of your body is immersed in the water. If you stand in water up to your waist, you will feel the water trying to push you up, but you will be able to resist it pretty easily. If you stand in water up to the bottom of your ribs, you will begin to float. If you stand in water as high as your armpits, you will have to fight to keep your feet on the bottom of the pool as the water tries to push you up. One of the great effects of buoyance is that the water starts to support your body and that takes the load off your muscles and joints. How much support?
| Depth of a 200-pound body in water | Share of weight supported by muscles and joints(%) | Share of weight supported by water |
| Waist high | 100 pounds (50%) | 100 pounds (50%) |
| Ribcage height | 70 pounds (35%) | 130 pounds (65%) |
| Armpit height | 60 pounds (30%) | 140 pounds (70%) |
Notice that, even if you are only submerged to your waist, the water picks up 50% of your body weight, leaving your muscles and joints with only half of the load they’re used to. As your body goes into deeper water, up to your armpits, the water supports an amazing 70% of your weight, substantially reducing the weight being supported by your muscles and joints.
For those of us with weight issues or joint issues, it feels like we’re almost flying when we get in water up to our armpits (which is the depth I recommend for you when you do Aqua Zumba). This is the key reason that physical therapists who are familiar with water exercise suggest their patients who have arthritis or bone-on-bone issues in their joints give water exercise a try. They can move their muscles and joints with less strain, which lets them get stronger without hurting. I consider buoyancy to be water’s superpower; it makes exercise much easier for everyone.
HYDROSTATIC Pressure
“Hydrostatic” comes from two Greek words meaning “water” and “standing”. Hydrostatic pressure is pressure from standing water. Because water is constantly pushing against the objects it encounters, it will push against your body from all directions. This has a few funny effects on your body.
First, your body is going to have to adjust its balance to keep you standing up — which is great practice for your brain to react to pressure.
Second, the water is producing a kind of massage against your body. This has the effect of making your blood flow more quickly than it would if you were standing in air, which lowers your heart rate, since your heart doesn’t have to work as hard to move the blood. Medical studies suggest that your heart rate is 5-10 beats per minute slower while doing exercise in the water than it would be if you were doing the same exercise on land.
Finally, the hydrostatic pressure actually helps you keep your balance. Imagine thousands of tiny little hands pushing on your body. If you begin to shake or fall, the little hands push you back into place. This makes doing exercises that are designed to improve your balance and reduce the chance of falling a lot easier because you are less likely to fall down while you are in the water.