Our aim was to evaluate the amount of tension present after incision and undermining of the anterior rectus sheaths and the external oblique muscles in 20 fresh adult cadavers. Resistance to traction of the anterior and posterior rectus sheaths towards the midline was measured at three stages of dissection: before any aponeurotic undermining; after incision and undermining of the anterior rectus sheaths; and after incision and undermining of the external oblique muscles associated with the previous dissection. Significance of differences was assessed using non-parametric tests. There was a significant reduction in tension in the anterior and posterior sheaths on both levels after each stage of dissection. The incision and undermining of the anterior rectus sheaths and the external oblique muscles promoted a progressive reduction in tension at the aponeurotic edges of the abdominal wall.