Muscles and ligaments need to be warmed up and stretched before any action as they are cold and stiff and not in a fit state to commence any muscle training.

Pre exercise stretching will push your muscles and ligaments beyond their normal limit. This has a combined effect that improves performance by increasing blood flow that enhances circulation and gives you more flexibility that allows you to move better. Stretching muscles for muscle training also helps prevent muscle and ligament injuries and I think that is the most important reason.

It is also very important not to over stretch during pre exercise stretching as you could tear the muscle or ligament.

After muscle training it is also beneficial to stretch muscles as this warming down period can help your muscles to recover from muscle training more quickly than they would normally.

How should you stretch muscles?

The muscle in question should be stretched until it is in the position that is under the point of any pain. You should never feel any discomfort. Do not use too much force. Hold the muscle in that position for maybe up to ten seconds or so and then slowly released the force. Never let the stretch go quickly.