OBJECTIVE: A new quantitative technique for measuring the trunk control capability/coordination was to be developed in this study. DESIGN: Fitts' experimental paradigm was employed to quantify the information processing capacity (bits/s) of the trunk as well as dynamic motor performance such as velocity and acceleration during flexion and extension. BACKGROUND: The quantification of functional capability of the trunk such as range of motion, strength, and endurance have been used to evaluate low back pain patient. Especially, dynamic trunk motion during flexion and extension has been studied not only to quantify the severity of the low-back impairment but to classify patients. METHOD: A lumbar motion monitor was used to record the time series of range of motion (RoM) and compute the velocity and acceleration of the trunk motion. Twenty male subjects without any back pain in the past 6 months and previous history of back injury participated. Each subject performed 22 controlled flexion/extension at predetermined RoMs as well as one ballistic trunk flexion/extension at a self-selected RoM. RESULTS: The information processing capacity of the trunk among healthy subjects was found to have a mean of 4.23 (SD 1.43) bits/s based on Fitts' law. Also, the velocity of dynamic trunk motion was measured with a considerable reduction in intersubject variability when the RoMs were controlled. A short but still accurate experimental protocol was suggested via a series of statistical analyses to provide an objective and easy-to-use method to evaluate the functional capacity of low-back pain patients.