Objective
The purpose of this study was to investigate a correlation between the muscle strength of trunk and bone mineral density (BMD) in women.

Method
A total of 218 healthy women participated in the study. Their age ranged from 26 to 72 years. Dual X-ray absorptiometry was used to measure the BMD of lumbar spine and the trunk muscle strength was assessed by a Cybex NORM^TM system. Under the standard criteria of World Health Organization for the dual X-ray absorptiometry analysis, we divided spine T-score into three groups(group 1: osteoporosis, group 2: osteopenia, and group 3: normal).

Results
The data revealed a siginificant correlation (r=⁣0.455, p=0.0001) between the age and BMD of lumbar spine. Trunk extensor muscle strength revealed 56.27⁑18.08 Nm (mean⁑SD) in osteoporosis group, 72.84⁑21.69 Nm in osteopenic group, and 77.90⁑22.28 Nm in normal group. Trunk flexor muscle strength was 82.73⁑23.30 Nm in osteoporosis group, 86.00⁑19.77 Nm in osteopenic group, and 98.91⁑18.29 Nm in normal group.

Conclusion
These results indicated that the trunk extensor muscle was weaker than the flexor muscle in osteoporotic group. As the bone mineral density reduced, the strength of both trunk extensor and flexor decreased. However the weakness of trunk flexor occurred at the earlier stage of osteoporosis than the weakness of trunk extensor.