The overall objective of this research is to relate disorders of the lumbar spine to the mechanics of the system. An isokinetic-isometric testing procedure was designed, and groups of normal subjects and patients with back pain were tested. The procedure allows sensitive detection of muscle weakness specific to some part of the range of motion or some functional contraction speed. A biomechanical analysis was performed on several parameters of back strength assessment to develop performance indexes that can be used in establishing screening modalities. Maximum torque and trunk angles are different in normal and patient populations.