The most effective exercise to enhance your abs is the twisting decline dumbbell sit-ups. Applying the exercise correctly will yield positive results. This exercise requires the decline bench set at a 30 degree angle. Lay down over the declined bench and make your back straight with the bench. Grab the pair of dumbbells and place them at the height of your shoulders. Your palms must be facing your feet. Pull yourself up by tensing your abs. At the same time, twist your right arm with dumbbells and bring it forward. Now by remaining seated uprigh, place your right arm across the left knee. Now, place your back down to get the beginning position. Repeat the process for the left arm. Decline bench and dumbbells Lay down on the 30 degree declined bench. Keep your back straight against the bench. Grab the pair of dumbbells and place the dumbbells at the height of your shoulders. Pull yourself upward and twist your right arm. Now place your right arm across left knee while seated. Lay back on the bench and repeat the process with the left arm.