Plank With Side Step - Anatomical Analysis This exercise is intended to strengthen the core muscles, with an emphasis on the oblique abdominals and hip flexors of the supporting leg, breaking leg contact adds to the difficulty level of the exercise! Start with an elbow plank. Break leg contact from the floor and move it sideways. Bring the second leg to the first, and repeat the same movement with the second leg. The external oblique is dominant on the side of the lifted leg, and the internal ob