Stretching.

This should always be done before and after exercise as a form of warm up or cool down. It involves holding positions that lengthen the muscles.
For a simple guide on how to stretch prior to or after exercise see Netfit.co.uk.
If you want a really in depth guide to stretching see Bath.ac.uk

Stretching has many benefits eg :-

1. Improved flexibility.
2. Improved circulation.
3. Improved posture.
4. Improved balance and co-ordination.
5. Helps one relax.
6. Can reduce lower back pain