The purpose of this study was to compare the change in lumbar flexors torque before and after a lumbar strengthening exercise among those who had received and those who had not received lumbar operation. The total of 49 subjects diagnosed with HNP were divided into two groups who had surgery (n=27) and had not (n=22). Comparisons were made before and after the exercise program in each group using paired t-test, and between groups using independent t-test. The results were as follows. The flexors torque on angle between groups before and after lumbar strengthening exercise of the patients did not show any statistical significance. The results suggest that the patients with low back pain would get a same treatment effect while the patients have a operation with a functional exercise treatment program aided by reinforcement exercise centering around the angle. It seems that muscle strength training with least strong regions around lumbar flexors on each angle instead of choosing a surgical treatment may be optimized unless they are exposed to a specific pathological conditions. Accordingly, customized exercises fit for patients and constant exercise therapy programs should be developed and applied for the patients who intend to strengthen their lumbar extensor for being free from pain and chronic lumbago.