The repair of incisional hernias can be accomplished by open or laparoscopic techniques. The Biodex(A (R)) dynamometer measures muscle strength during isokinetic movement. The objectives of this study are to compare the strength of the trunk flexors between patients who underwent repair for incisional hernia and a control group, and to compare trunk flexion after two kinds of operative techniques for incisional hernias with and without approximation of the rectus abdominis muscles. The trunk flexion of 30 patients after different operative techniques for midline incisional hernias and of 12 healthy subjects was studied with the Biodex(A (R)) isokinetic dynamometer. The mean torque/weight (N m/kg) for trunk flexion was significantly higher in the control group compared to the patient group after incisional hernia repair. A significantly higher peak torque/weight [coefficient 24.45, 95% confidence interval (CI) -0.05; 48.94, P = 0.05] was found in the two-layered suture technique without mesh compared to the laparoscopic technique after adjusting for gender. The isokinetic strength of the trunk flexor muscles is reduced after an operation for incisional hernia. There is some evidence that a two-layered suture repair with approximation of the rectus abdominis muscles results in higher isokinetic strength of the trunk flexor muscles compared to the laparoscopic technique.