To evaluate the deficits in trunk flexion due to partial or complete unilateral rectus abdominis muscle flap transfer in reconstructive surgery, 27 patients (11 females, 16 males) with rectus abdominis muscle flap transfer dating back at least 3 years, clinically healthy at the time of testing, and 22 controls (10 females and 12 males), comparable in age and body mass index, were compared. For clinical assessment of power of the straight and oblique abdominal muscles, Janda's test of muscle function was used, and torque (in N.m) of isometric trunk flexion at 0, 5, 10, 20, and 30 degrees was determined with the TEF Modular Component, an auxiliary unit of the Cybex 6000. Results were analyzed for males and females separately. Relative torque (N.m/kg) of operated male and female patients was significantly lower (p < 0.05) as compared with controls. Differences were more pronounced in males than in females. Clinically, there were no significant between-group differences in the power of the straight and oblique abdominal muscles. In conclusion, trunk flexion deficits following rectus abdominis muscle flap transfer can be compensated for satisfactorily in most cases, supporting the use of this muscle in reconstructive surgery, if patients are selected carefully.