Exertion-Driven Strength Modeling of the Shoulder Clark Dickerson and Don B. Chaffin Proceedings of SAE Digital Human Modeling for Design and Engineering Conference, Arlington, VA, June 26-28, 2001. Human strength modeling often focuses on static, isometric maximum voluntary contractions. Often neglected, however, is the dynamic nature of many reaching exertions. Of particular interest to the applied biomechanist are activities that involve dynamic exertions that require variable forces to be produced at the hands, as these are common workplace requirements. In reaching tasks, when the shoulder is used to perform motions both in loaded and unloaded states, the shoulder is a joint of primary concern. Effective knowledge of the mechanical stresses on this joint has received much attention in the literature. However, there are few dynamic experimental designs that explore the vast differences in task specificity. This investigation elucidates the relationship between task requirements and resultant dynamic effects at the shoulder joint. It is well known that muscle activity is greatly changed in concentric and eccentric activity, when compared to isometric, static exertions. The interplay between changes in muscle and tendon length and load sharing during contraction raises many questions regarding the accuracy of static models. By accounting for several dynamic variables, the prediction of muscle force, and hence the increased risk of injury, could potentially be improved substantially. This paper will describe progress being made to understand the role of shoulder muscles in dynamic reaching tasks. abs2001_03