The purpose of this thesis was to determine whether the understanding of spine movement dysfunction, as indicated by abnormal displacement, velocity, and torso moment data measured by a clinical evaluation system (Isostation B-200), was augmented by a flexion-extension task and the knowledge of the EMG activity from select abdominal and back extensor muscles and/or by knowledge of individual torso tissue forces, estimated from an EMG assisted, dynamic, three dimensional spine model. Because individuals symptomatic for low back pain could not produce true Maximal Voluntary Contractions (MVCs) which were needed for scaling the model’s EMG inputs, a method was developed which successfully replaced the MVC scaling factor by an EMG-to-Force (EMG_Force) scaling factor. Model outputs using the MVC and EMG_Force methods were compared for 10 asymptomatic and 4 symptomatic males for a freestyle flexion-extension task. The EMGForee method produced significantly lower compressions and flexor muscle forces, but no difference was found in extensor muscle force.

The EMG_Force method was then used to investigate the understanding of spine movement dysfunction. Four males symptomatic (SYMP) for recurrent low back pain and 10 asymptomatic (ASYMP) males were each evaluated on two days. The SYMP group were tested on days they identified as “Good” or “Bad”. Each day they were tested using the Isostation B-200 and performed a flexion-extension task with hand loads of 0, 5 and 10 kg. The B-200, EMG and model output data from the ASYMP group were used to develop custom profiles for each of these methods. Muscle force data, presented as an Amplitude Probability Distribution Function (APDF) quantified differences between the groups by determining the amount of time that the forces were above a criterion level. Improved functionality was associated with decreases in excessive spinal flexor and/or extensor muscle force production and the flexion component of the flexion-extension task was better for distinguishing an SYMP individual from the ASYMP group. The EMG profiles (mV, %MVC) did not distinguish the SYMP group or reveal the improved function. Performance profiles for the B-200, EMG and the model were found to augment the understanding of spine movement dysfunction.