BYT

Hinge · Bodyweight · Learn first

Back extension

Pad just below the hip crease, ankles locked. At the top the body is one straight line.

Back extension
  1. 1Fold at the hips, back flat, until you feel the hamstrings.
  2. 2Rise by squeezing the glutes, not by throwing the head back.
  3. 3Stop when the body is straight. Don't hyperextend.

Easy to miss: Rounding and then whipping the spine upright.

Muscles

Copper on the figure is a prime mover. The softer tone helps.