Objective
To evaluate (1) the effect of chronic low back pain on bone mineral density, and (2) the effect of chronic low back pain on trunk muscle strength in women.

Method
Subjects were 118 women patients (ages of 28∼65 years) suffering from chronic low back pain more than three months and control groups were 218 healthy women (age of 26∼72 years). We measured bone mineral density (BMD) at the lumbar spine and proximal femur using Dual X-ray absorptiometry and trunk muscle strength using Cybex 660 dynamometer.

Results
There was no significant difference between groups in lumbar spine BMD, in proximal femur BMD, or in trunk flexor muscle strength. However, trunk extensor muscle strength was reduced significantly in patient group. Trunk extensor muscle peak torque was 64.69⁑18.48 Nm in the patient group and 73.84⁑22.50 Nm in the control group in 30^o/sec, and 58.65⁑18.59 Nm in the patient group and 65.68⁑20.28 Nm in the control group in 60^o/sec.

Conclusion
The results suggest that chronic low back pain does not affect the BMD. However, it causes trunk extensor muscle weakness; therefore, trunk extension exercise will be help to the patients with chronic low back pain.