This exercise is suitable for strengthening the muscles of the abdomen.
Lie down into supine position on the ground in such way that your waist is tightly on the ground. With your knees slightly bent lift your straight legs to a square position with your torso. Let one of your straight legs down so that it will be parallel with the ground but pay attention not to put it down. Then lift it back next to the other leg then repeat this with your other leg. Perform the exercise with alternate legs in a proper repetition number. Pay attention that your waist should be on the ground all the way so that you can avoid back pains and to maintain the tension in the muscles of the abdomen.