Spinal manipulative therapy (SMT) is a complementary therapy frequently used to treat low back pain (LBP). Current theories propose that SMT corrects abnormal lumbar intersegmental motion, but the detection and characterization of in vivo intersegmental motion are not well established. Thus, the effect of SMT on intersegmental motion is unknown. Our broad, long term objective is to investigate the effect of SMT on lumbar intersegmental motion and to determine the relationship between the clinical effects of SMT and intersegmental motion changes. To accomplish this, it is necessary to develop an efficient, accurate and reliable method of measuring in vivo intersegmental motion. Videofluoroscopy holds promise of providing continuous motion data with low radiation exposure but data processing methods have not reached a level of sophistication that enables efficient clinical use; they still require manual identification of landmarks and explicit vertebral segmentation. We hypothesize that 2-D intersegmental kinematics of the lumbar spine can be efficiently and accurately quantified from videofluoroscopic images. We propose to test this hypothesis by addressing the following Specific Aims: 1) Develop an automated software application to quantify 2-D intersegmental kinematics in the lumbar spine from dynamic videofluoroscopic images. This application, based on existing modules within the Analyze biomedical imaging programming environment, will quantify intersegmental rotation and translation of the center of rotation, and global (L2-L5) lumbar motion. 2) Conduct dynamic in vitro spine testing to establish the accuracy and limitations of assessing 2-D intersegmental kinematics using an automated software application (Aim 1). Fluoroscopic images of in vitro lumbar motion will be obtained simultaneously with kinematic parameters from an optoelectric tracking system of known accuracy. Kinematic data from the automated software will be compared to the optoelectric tracking system data. 3) Assess the reliability of measuring in vivo lumbar intersegmental motion parameters from videofluoroscopic images of active lumbar flexion, extension, and lateral bending in asymptomatic subjects and subjects with chronic LBP using an automated software application (Aim 1). Videofluoroscopic images of 10 asymptomatic subjects and 10 subjects with chronic LBP will be obtained at two time points. Reliability of kinematic parameters from the software application will be determined. Parameter means and variation (among and within subjects) will be calculated. Trends that might lead to new hypotheses of the effects of SMT on intersegmental motion will be examined. The novel software application developed and tested in this project will enable studies that directly test the primary biomechanical rationale for treating low back pain with SMT. It will also enable us to conduct clinical studies that refine the application of SMT in terms of location, type and dose.