This is literally one of my favorite deep core routines to do. It's simple, but it's definitely a tough one.
• Reverse plank - Exhale as you lift your hips. Inhale as you lower them back down.
• Reverse plank march - Exhale as you lift your leg. Inhale as you lower it back down.
• Reverse plank leg lift - Exhale as you lift your leg. Inhale as you lower it back down.
• Reverse plank hold - Exhale as you lift your hips up. Breathe normally at the top.
3-4 sets of 10-12 reps