Objective
To measure lumbar multifidus muscles by ultrasonography and to study its correlation with the isometric peak touque of back.

Method
Bilateral L5 and S1 multifidus muscle sizes of 18 healthy volunteers were measured in prone position by ultrasonography with 7.5 MHz, 40 mm-length probe. Multifidus muscles were identified using anatomic landmark-spinous process and lamina and vertical and horizontal diameter were measured. Boundary of muscle was traced and cross sectional area was measured.

Lumbar spinal range of motion (ROM) and isometric peak torque of three axes-flexion/ extension, rotation and lateral flexion-were measured by Isostation B-200^R back muscle tester.

Results
Multifidus muscle cross sectional areas were well correlated with isometric peak torque in all direction of movements. Muscle size and lumbar spine ROM showed no correlation.

Conclusion
Ultrasonographic measure of lumbar multifidus muscles could be a useful tool to estimate back muscle function.