Start with your hands by your sides on p-bars or some other object to elevate you higher off the floor. The shorter the object the more challenging this position becomes. Push into the ground hard with your arms, keeping your shoulders firmly packed down. Tuck one leg in towards your chest and lift the foot of your other leg off the floor, locking that leg in a straight line. Hold yourself up for the desired amount of time.

Hip Flexors, Core - Abdominals

Hinge