Agility is the ability to change body position or direction of the body rapidly. This ability is measured with running tests that require the subject to turn or start and stop. Agility is also influenced by balance, coordination, position of center of gravity, running speed and skill. Agility can be improved by practicing specifically for a sport but also by improving the specific individual elements of speed, balance, power and co-ordination.
Agility is always a difficult area to test. The agility demands for different sports is very specific, in terms of the speed and direction of turning, and includes extra factors like controlling a ball or holding a stick. Many tests involve complex movements, what is actually being measured may not be clear, and a good score may hide deficiencies in some aspect of agility.
When testing you need to decide of which aspect of the sport specific testing you want to investigate. Some research suggest that for example turning at 90 degrees is very different to turning at 120 degrees, and being good at one doesn't necessarily mean you will be good at turning at the other. It is also possible that turning in one direction, e.g. turning left, will be worse than turning right.
You have to be careful in the interpretation of agility tests as you need to know what they are exactly measuring. It is better to break down the agility movements you want to measure into individual factors and measure each individually, such as turning left versus turning right, turning at different angles. It is often easier to just make up the tests yourself, as differences in surfaces used often make comparisons to other norms difficult.