The hot spot: The piriformis is a thin, pear-shaped muscle that connects the front of the sacrum to the greater trochanter, which is "a big bony lump on the side of the thigh," says Miller. When we walk, shift our weight or maintain balance, it's one of six muscles that stabilize the hip joint, as it lifts and rotates the thigh away from the body.
The problem: The piriformis lies above the sciatic nerve, the largest nerve in the thigh. When the piriformis becomes inflamed from running or climbing stairs, or is chronically shortened from sitting for long periods of time, it puts intense pressure on the nerve.
The potential pain: Inflammation, tingling or numbness deep in the glutes that can shoot down the length of the leg, or up into the lower back.
The pre-hab: Because this muscle is nestled so deep in the butt, it's hard to locate or massage with your hand, Miller says. Here's her trick for getting at it: Lie on your back with your feet flat on the floor and knees bent. Place the tennis balls (or Yoga Therapy Balls) on both sides of your sacrum and let your knees fall open into a butterfly position. Inhale and strongly contract your buttock muscles. Hold your breath and the move for a count of 4, then exhale and let the balls nuzzle deeper into the buttocks. Repeat the contracting/relaxing along with the breath 6 to 8 times. Then, take the right ball out, place the right foot flat on the floor, lean into the left ball and roll it from the sacrum across the left cheek toward the side of the hip. Do this for about 90 seconds, letting the ball trace its way from sacrum to hip. Repeat on the opposite side.