This seems a simple question, but it's a very good one, and is a part of every tummy tuck consultation.There are three elements the surgeons considers when evaluating you for a tummy tuck: The skin, the thickness and evenness of the fat layer under the skin, and the state of the abdominal wall.Based on the evaluation, a surgical plan is made planning removing the skin excess if it is present, thinning out and making more even the fat layer, and repairing or strengthening the muscle layer if it is stretched and loose, or if there is a rectus diastasis, or gap, between the rectus muscles.Basically, it is not usually necessary to do a muscle repair if there has not been a pregnancy. There are exceptions to this after massive weight loss, but it is not common.If there have been pregnancies, one of four situations occurs.1. The muscle wall is firm, and there is no gap between the muscles. In this case, no muscle repair is required.2. There is no gap between the muscles, but the whole abdominal wall sheath is stretched, leading to a lower abdominal bulge. In this case, an anterior sheath plication tightening is required.3. There is a gap which can be detected between the muscles, but it is not large, the abdominal wall sheath is strong, and there is no bulge forward with activation on clinical exam. In this case, usually no muscle repair is necessary.4. There is a gap between the muscles, and on clinical exam a bulge on muscle activation is seen. In this case a muscle repair is necessary.The plan as to whether to repair the muscle or not is made during a cereful clinical exam by the surgeon. The issue is not whether there is a gap, but whether ther is a bulge on muscle activation. Ultrasound, or other radiology examinations, are not very useful, as the bulge is usually seen on muscle activation, especially twisting or flexing. This can be diagnosed on clinical exam.So, in summary, it is usually able to be determined in the preop assessment whether a muscle repair is going to be required. It's important to have it planned, as if you don't need a muscle repair the operation is less painful and has a faster recovery. Where there is doubt whether the repair is needed, and there is in some cases, it is usually better to do it.All the very best,Howard WebsterPlastic Surgeon.