Muscle energy is an Osteopathic way of mobilizing the spine by using opposing or antagonist muscles to turn off a muscle, attached to the spine, that pulls the spine out of alignment. This is because our bodies are programmed to relax muscles that oppose the motion that we move a joint. For example when we straighten or extend our knees, the muscles that bend or flex our knees are inhibited. This is a gentle technique to realign the spine.
More information can be found at these webistes
https://www.studentdoctor.net/blogs/omtguru/2006/12/osteopathic-manipulative-treatment-what.html