The hip flexors are the most important muscles in the front part of your torso. They maximize your knee elevation, helping you rapidly get to the next step. They also help prevent those infamous sports hernias by strengthening the transverse (horizontal) abdominal muscles. Groin strains are even prevented by hip flexor strength work. The goal is to perform this exercise with your hands on your stomach and without holding on to the floor. When you can do this with hands on your stomach, place a foam roller longitudinally under your spine and repeat with the goal of again doing this exercise with hands on your stomach. Now you will engage even more core muscles.
Dr. Paul R. Copeskey, DC, CCFC
Abdominal and Hip Flexor Strengthening Exercises