Piriformis syndrome is a type of neurological injury that is caused by compression of the sciatic nerve. The piriformis muscle sits deep within the buttock, behind the gluteus maximus. It starts at the lower spine and connects to the femur muscle. This nerve can become compressed from swelling of the piriformis muscle due to injury or muscle spasms or inflammation. Piriformis syndrome causes symptoms including pain in the back of the thigh, pain in the back of knee, buttock pain, pain in the calf, pain in sciatic nerve branches (pain in the nerves of leg and the buttocks, then), shooting pain in the legs, and hip pain after sitting.
Squats. Using a squat machine will strengthen your quadriceps muscles on the front of your thigh and the hamstring muscles on the back of your thigh, both of which attach to your hip and give it support. The squat machine may be vertical, in which case you’ll start in a standing position and bend your knees until your thighs are parallel to the floor, or it may be on a sliding incline board.
• Psoriatic arthritis. Psoriatic arthritis is a form of arthritis accompanied by the skin disease psoriasis. The skin disease often precedes the arthritis; in a small percentage the joint disease develops before the skin disease. For about 20 percent of people with psoriatic arthritis, the disease involves the spine. In some cases, bony overgrowth can cause two or more vertebrae to grow together, or fuse, causing stiffness.

The hips are the cornerstone of every runner’s body. Comprising an array of muscle groups—from the all-powerful glutes to the smaller hip flexors and adductors—your hips propel every stride, stabilize the thighs, and (quite literally) keep the knee on the right track, physical therapist John Sauer, D.P.T., O.C.S., an endurance program manager with Athletico Physical Therapy, tells SELF.
How to: Lie on your back with your right knee bent and foot flat on the floor (a). With your left leg fully extended, press into your right foot to shift onto your left hip. This is your starting position (b). Then, squeeze your right glutes to press your left hip open until you feel a stretch, pause, then return to start. That’s one rep (c). Perform six to eight reps, then repeat on the opposite side.
You're more likely to get a hip flexor injury if you've had one in the past, you don't warm up properly before engaging in athletic activity, your muscles are already tight or stiff, or your muscles are weak from being overused. If, while exercising, you try to do too much at once in too short an amount of time, you can also put yourself at risk for a hip flexor injury.
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