Also called the Monster Walk, this standing ab exercise will target the often forgotten Psoas. This muscle is located in your lower abdomen where it crosses the hip joint from your lower spine to your inner thigh. This move strengthens the psoas by hip flexion and extension. The stronger this muscle is, the more it can support your lower spine and reduce deep back pain. Bonus! Frankensteins hit the gluteal muscles that lie behind your hip joints --quite difficult to tone! 1. Put both hands in the air, belly button pulled in. 2. Kick your right leg up to hip level and touch your toes with your left hand. 3. Switch legs and repeat.