The Piriformis muscle lies deep in the buttock, behind the gluteus maximus. Even though it is a small muscle, the Piriformis has many important functions, including:

• Assisting movement of the lower body
• Stabilizing the pelvic and hip joints
• Maintaining balance of the pelvis when weight is transmitted from one leg to another
• Assisting during rotation 

When your glutes and piriformis are tight they can cause one to have a sore lower back, tight hamstrings, poor balance, and even sciatica. Sciatica is pain that radiates along the sciatic nerve, which runs down one or both legs from the lower back and can be excruciating and debilitating. Stretching can help prevent sciatica, as well provide pain relief by loosening your gluteal and piriformis muscles that can become inflamed and press against the nerve.