The properties of water are the key to the benefits: 
- Hydrostatic pressure – the pressure of the water on the limbs and body under water provides a support similar to an all-over support hose! This is particularly good for relieving any swelling, but because of this property of water, dogs with a respiratory or cardiac condition are not advised to swim due to the pressure against the chest wall.
- Viscosity – this property provides the resistance to movement – it gives friction. Water provides much more resistance than air giving us more exercise in a shorter time without overly stressing the joints with percussion. The resistance is on all planes of movement, so the dog is working multiple sets of muscles at the same time – each movement is concentric and eccentric. On land, gravity assists so the muscles are used more in one direction than the other. It also slows any ballistic movement, which decreases the chance of injury.
- Buoyancy – the force that allows a body less dense than water to float. This means that the effects of gravity are greatly decreased – the body’s weight is reduced by 75% – 90%, depending on one’s body type (density), and how deep one is immersed. (Muscle is denser than fat, which is why heavily muscled dogs are less buoyant.) This force allows dogs to exercise without putting weight or percussive stress on the joints.