CrossFlowV: Lower Abdominal Strength. 27 minutes. Whether you have back problems, are a new or new-ish mama, this flow is for YOU. Every move aims to activate your lower abdominals and pelvic floor. Just because six pack abs are pretty doesn't mean they protect your spine. THEY DON'T (on their own)! Blocks for the last move are great, but not necessary. So, grab your mat, and GET STRONG!