The selection of an appropriate and/or standardized method for representing 3-D joint attitude and motion is a topic of popular debate in the field of biomechanics. The joint coordinate system (JCS) is one method that has seen considerable use in the literature. The JCS consists of an axis fixed in the proximal segment, an axis fixed in the distal segment, and a "floating" axis. There has not been general agreement in the literature on how to select the body fixed axes of the JCS. The purpose of this paper is to propose a single definition of the body fixed axes of the JCS. The two most commonly used sets of body fixed axes are compared and the differences between them quantified. These differences are shown to be relevant in terms of practical applications of the JCS. Argumentation is provided to support a proposal for a standardized selection of body fixed axes of the JCS consisting of the axis ê1 embedded in the proximal segment and chosen to represent flexion-extension, the "floating" axis ê2 chosen to represent ad-abduction, and the axis ê3 embedded in the distal segment and chosen to represent axial rotation of that segment. The algorithms for the JCS are then documented using generalized terminology.

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. Purpose: The purposes of this project were to assess the effect of four different shoe inserts on the path of the center of pressure (COP), to quantify the effect of these inserts on selected knee joint moments during running, and to assess the potential of COP data to predict the effects of inserts/orthotics on knee joint moments. Methods: Kinematics for the lower extremities, resultant ankle and knee joint moments, and the path of the COP were collected from the right foot of 15 male subjects while running heel-toe with five different shoe inserts (full or half with 4.5-mm postings). Results: Individual movement changes with respect to the neutral insert condition were typically small and not systematic. Significant changes for the path of the COP were registered only for the full lateral insert condition with an average shift toward the lateral side. The mediolateral shift of the COP was not consistent for the full medial and the two half-shoe inserts. The subject-specific reactions to the inserts' intervention in the corresponding knee joint moments were typically not consistent. Compared with the neutral insert condition, subjects showed increases or decreases of the knee joint moments. The correlation between the individual COP shifts and the resultant knee joint moment was generally small. Conclusion: The results of this study showed that subject-specific reactions to the tested inserts were often not as expected. Additionally, reactions were not consistent between the subjects. This result suggests that the prescription of inserts and/or orthotics is a difficult task and that methods must be developed to test and assess these effects. Such methods, however, are not currently available.

Impact forces have been speculated to be associated with the development of musculoskeletal injuries. However, several findings indicate that the concepts of “impact forces” and the paradigms of their “cushioning” may not be well understood in relation to the etiology of running injuries and that complex mechanisms may be responsible for injury development during running. The purposes of this paper are (a) to review impact mechanics during locomotion, (b) to review injuries and changes of biological tissue due to impact loading, and (c) to synthesize the mechanical and biological findings. In addition, directions for future research are discussed. Future research should address the development of noninvasive techniques to assess changes in the morphology and biochemistry of bone, cartilage, tendon, and ligaments; researchers should also try to simulate impact loading during activities such as running, focusing on the interaction of the various loading parameters that determine the acceptable windows of loading for biological tissues.