In order to harvest tissue from the abdomen for use in breast reconstruction, the rectus abdominus ("6-pack") muscles must often be dissected. This allows the surgeon to follow the perforating blood vessels from the deep blood vessels (in this case, the Deep Inferior Epigastric artery) to the surface of the abdominal soft tissue. The rectus muscles, in conjunction with the erector spinae (lower back muscles), are crucial for providing stabilization of the torso. Based on the degree of perforator dissection, part of the rectus muscle can become paralyzed or devitalized (without blood flow). This can result in imbalanced forces on the torso, and soreness of the lower back can result. Once cleared by the surgeon for postoperative exercise, a physical therapy regimen can help to relieve muscle tension and strengthen the abdominal musculature.