High Quality Content by WIKIPEDIA articles! The vacuum exercise is an exercise which involves contracting some internal abdominal muscles, primarily the Transversus abdominis muscle, and not as much the diaphragm, the "six pack" muscles or "abs" which are trained through crunches, leg raises, or other core exercises. Repetitions of the exercise may be used as a form of endurance training, and light strength training. There is difficulty building strength in the muscle, as resistance training is difficult for internal muscles.