MODELING OF FUNCTIONAL TRUNK MUSCLE PERFORMANCE - INTERFACING ERGONOMICS AND SPINE REHABILITATION IN RESPONSE TO THE ADA

The combination of increasing costs of musculoskeletal injuries and th e implementation of the Americans with Disabilities Act (ADA) has crea ted the need for a more objective functional understanding of dynamic trunk performance. In this study, trunk extensor and flexor strengths were measured as a function of angular position and velocity for 20 su bjects performing maximum isometric and isokinetic exertions. Results indicate that trunk strength is significantly influenced by trunk angu lar position, trunk angular velocity, gender, and direction, as well a s by the interaction between trunk angular position and velocity. Thre e-dimensional surfaces of trunk strength in response to trunk angular position and velocity were constructed for each subject per direction. Such data presentation is more accurate and gives better insight abou t the strength profile of an individual than does the traditional use of a single strength value. The joint strength capacity profiles may b e combined with joint torque requirements from a manual material handl ing task, such as a lifting task, to compute the dynamic utilization r atio for the trunk muscles. This ratio can be used as a unified measur e of both task demand and functional capacity to guide job assignment, return to work, and prognosis during the rehabilitation processes. Fu rthermore, the strength regressions developed in this study would prov ide dynamic strength limits that can be used as functional constraints in the computer simulation of physical activities, such as lifting. I n light of the ADA, this would be of great value in predicting the con sequences of task modifications and/or workstation alterations without subjecting an injured worker or an individual with an disability to u nnecessary testing.