Muscles involved: hip and knee extensors, hip abductors
Form: stand with feet shoulder width apart, holding DB, MB, or body bar if you want. Brace core, and inhaling, take lead leg behind you and drop into a lunge position, keeping front leg knee behind the toes, and not allowing the rear leg knee to hit the floor. Drive your weight through the front heel, exhale and return to start; switch legs or do all on one side before switching.
Cautions: Keep the spine aligned properly, no spinal flexion or arching. Keep knee from extending over toes.
Trainer techniques: Cue breathing, braced core, contractions in gluteals and quads, watch for proper position of the spine and pelvis, and observe the motion at the hip, knee and ankles. Spot with your hands under the rib cage.