The pretzel side kick is a basic, single-joint exercise that strengthens the glutes while also improving stability and mobility of the hip joint.
Lie on your side with both knees bent and stacked on top of one another, with your torso propped up and supported on one forearm. One foot should be slightly behind the other.
Keep your spine straight by bracing your abs and lifting your chest up. Lift your top knee off the floor, and kick your leg out to the side. Keep it parallel to the floor. Return you left leg to the starting position. Do all reps, switch sides and repeat.
Do not slouch your torso forward during the kick.
Do not let the kicking leg droop to the floor.
Squeeze your abs and glutes to help with stability.