I get this question quite a bit – and there’s a few different answers.
For starters, many, many people have trigger points in their back. It’s one of the commonest places.
One of the major causes of lower back pain is a muscle called the quadratus lumborum (QL for short). This muscle is quite deep, and really the best way to reach it is when you’re lying down.
This is because when you’re lying down the muscles over the quadratus lumborum aren’t active. So it’s much easier to get down to the QL muscle and switch off its triggers.