Properties of Water

Continuing our series of the properties of water with Leverage, Density and Hydrostatic Pressure, read this to complete your studies on the properties of water.


Shorter levers require less force than longer levers to move through the same distance through the same resistance. E.g. fwd kicks - fwd knee lifts, jacks with bent arms - jacks with straight arms.


Specific gravity of water is 1, so

Relative density > 1 will sink

Relative density < 1 will float

Specific gravity of the human body is generally between 0.96 and 0.974 therefore people float. When all air is expelled this increases to 1.050 - 1.084 therefore humans sink when the lungs are empty.

People with a higher muscle mass have a higher relative density and are more likely to sink as muscle has a higher relative density than fat.


This is the pressure exerted by any fluid on the body at rest. The body never rests in water therefore the synergistic muscles and fixator muscles are constantly working to stabilise the body. This means it is important to cue core muscles.

Hydrostatic pressure is equal on all body surfaces however it increases with depth of water. Pressure of water around the rib cage makes it harder to fill the lungs, (shallow breathing may occur) – encourage clients to take deep breathes and consider the effects on asthma sufferers in deep water.

This pressure also assists venous blood return to the heart which can cause lower heart rates in water exercise than land based. It also improves circulation and decreases the effect of blood pooling.

It can also increase the need to go to the toilet!

None of these physical laws of water act alone - a combination of forces will always be at work!

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