Muscles involved: hip, knee and spinal extensors
Form: Stand with feet hip width apart, holding a DB in each hand. Brace core, inhale as you squat down, aiming for your upper thighs to be almost parallel to the ground, and a 90 degree angle at the hip. Drive your weight through your heels as you exhale and return to start position.
Caution: keep knees from extending over the toes
Trainer techniques: Cue breathing, 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.