Get on your hands and knees on the floor. Tighten your stomach muscles by blowing all of your air out. Bring one leg up straight behind you and hold it in this position. Be careful not to rotate your pelvis. Start holding this for 5 seconds and as you gain strength lengthen the time that you hold it. Repeat this doing the opposite leg. Alternate the legs as you do this. As you gain strength, raise the opposite arm in front of you and hold this position as you did above.