Muscles involved: hip, knee and spinal extensors
Cautions: Keep knees from extending over toes. Choose an appropriate weight to protect the lumbar spine.
Form: start with feet hip width apart, a barbell held with alternating grip, start in squat position with flexion at hips, knees, and ankles, aiming for a 90 degree angle at the hip, and keeping the knees from extending over the toes. Brace core, breathe in, slowly come up out of the squat position to standing as you exhale.
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.