Certain machines can assist in toning your lower abs because you can select the amount of resistance you can add to make a move more difficult, Babidiye says. The ab crunch machine is one of them. Select the right resistance for you, but not too heavy. Bend your arms at a 90 degree angle. Lift the legs up as you crunch your torso. Do this motions slowly; focus on engaging the abs while relaxing your arms and feet.