Back extensions is an intermediate level core exercise. Start lying on your stomach with your hands on the ground under your chin. Simulaneously lift both arms and both legs 4-8 inches off the ground. Be sure to keep your next relaxed and lift your legs from the hips so that your legs remain straight. Slowly lower your arms and legs just before they touch the ground and repeat.
Core | Intermediate | Erector Spinae (Lower Back)