The piriformis is a muscle which extends from the sacrum (the bottom of the back/top of hips) to the top of the femur (thigh bone). It extends across the sciatic nerve, which runs from the lower back, down the back of the leg, into the toes. When the piriformis is inflamed or irritated, it can press on the sciatic nerve and give sciatica type symptoms. Sciatica can be a very painful condition, causing pain and/or numbness to extend down one or both legs, making it difficult to walk, stand or sit.
I have found in my massage practice in York that a deep but sensitive massage of the piriformis muscles can bring great relief.