The purposes of this study were to measure the normal value of peak torque of lumbar extensors at various degrees of lumbar flexion and to compare this with the chronic low back pain patient. 100 normal subjects, 70 men(age, 49.0±5.3) and 30 women(age, 48.1±7.4), completed isometric lumbar extension strength test. 26 low back pain subjects, 9 men(age, 35.3±14.7) and 17 women(age, 42.6±10.1), completed isometric lumbar extension strength test. Normal male peak torques of lumbar extensors were 125±38 Ft-lbs at 0 degree, 164±43 at 12 degree, 200±43 at 24 degree, 221±46 at 36 degree, 241±50 at 48 degree, 257±50 at 60 degree, and 262±51 at 72 degree of lumbar flexion. Normal female peak torques of lumbar extensors were 78±24 at 0 degree, 105±27 at 12 degree, 120±38 at 24 degree, 135±35 at 36 degree, 142±37 at 48 degree, 151±40 at 60 degree, and 157±41 at 72 degree of lumbar flexion. Normal peak torques of lumbar extensors increase as degrees of lumbar flexion increase. Body weight is more correlated with peak torque than body mass index. Male peak torques of lumbar extensors with low back pain were 91±47 Ft-lbs at 0 degree, 129±46 at 12 degree, 156±57 at 24 degree, 178±61 at 36 degree, 197±54 at 48 degree, 217±61 at 60 degree, and 218±52 at 72 degree of lumbar flexion. Female peak torques of lumbar extensors with low back pain were 45±24 at 0 degree, 73±28 at 12 degree, 98±32 at 24 degree, 117±44 at 36 degree, 130±40 at 48 degree, 138±41 at 60 degree, and 148±36 at 72 degree of lumbar flexion. Peak torques of lumbar extensors with low back pain increase as degrees of lumbar flexion increase. Comparison of the normal male peak torque of lumbar extensors with low back pain group revealed statistical differences at 48 and 72 degree of lumbar extensors. And the female group revealed statistical difference at 0, 12, and 24 degree of lumbar flexion.