Lower body lifts are most commonly performed after large weight loss. The same stresses that stretch the skin, can also stretch the abdominal muscles. It is common to tighten the case (the fascia) of the abdominal muscles with a lower body lift much the same as it is done with a tummy tuck.
The muscle is imbricated and repaired at the midline. This can be done with, or without a vertical scar on the abdomen. The vertical scar is added to a lower body lift, or a tummy tuck, when there is too much loose skin on the upper abdominal wall.
Sometimes I will also tighten the external oblique fascia to further hourglass the muscular contours. Muscle tightening of the sides and back is not normally needed, as the ribs and spine provide added support, and prevent the muscles from being stretched.
I hope this answers you question. Additional information is available on the video attached to this posting.