Why warm-up?

Warm ups.

Warming up before exercises has been shown to prevent injury and also increase performance.

The best way to know if you’re warmed up is to reach 55% of your maximum heart rate.
Maximum heart rate = 220 - your age
This also is the point where most people would pick up a slight sweat.

Secondly, it is important to bring your joints and muscles into the same range and movements that you will be doing in your sport or training. It is important to use dynamic stretches in the warm-up because static stretching may actually be detrimental to your performance.