An examination of undergraduate research in the field of biomechanics across multiple US-based institutions.

Undergraduate research is commonly performed in many STEM disciplines and has a wide array of benefits for students, laboratories, principal investigators, and institutions. While many fields have assessed best practices and the cost-benefit analysis of incorporating undergraduates in research, this has not yet been addressed in biomechanics. This paper represents the perspectives of seven members of the American Society of Biomechanics (ASB) Teaching Biomechanics Interest Group (TBIG). These TBIG members discussed their own experience regarding the opportunities, challenges, and benefits of undergraduate research and this perspective paper presents the commonalities found during these interactions. The TBIG members reported that undergraduate research was assessed similarly to graduate student research, which often led to an underestimation of productivity for both the student and overall lab output. While undergraduate researchers are not often responsible for publications and grant funding, they are instrumental in lab productivity in other ways, such as through human subject approvals, conference abstract presentations, student thesis projects, and more. Students benefit from these experiences, not necessarily by continuing in research, but by learning skills and making connections which further them in any career. While this perspective presents the experience of seven professors in the United States, future studies should further assess the cost-benefit relationship of working with undergraduates in biomechanics research on a global scale. A clearer picture of this analysis could benefit students, faculty, and administrators in making difficult decisions about lab productivity and assessment.

Benchmarking of dynamic simulation predictions in two software platforms using an upper limb musculoskeletal model.

Several opensource or commercially available software platforms are widely used to develop dynamic simulations of movement. While computational approaches are conceptually similar across platforms, technical differences in implementation may influence output. We present a new upper limb dynamic model as a tool to evaluate potential differences in predictive behavior between platforms. We evaluated to what extent differences in technical implementations in popular simulation software environments result in differences in kinematic predictions for single and multijoint movements using EMG- and optimization-based approaches for deriving control signals. We illustrate the benchmarking comparison using SIMM-Dynamics Pipeline-SD/Fast and OpenSim platforms. The most substantial divergence results from differences in muscle model and actuator paths. This model is a valuable resource and is available for download by other researchers. The model, data, and simulation results presented here can be used by future researchers to benchmark other software platforms and software upgrades for these two platforms.

Computational Development of Jacobian Matrices for Complex Spatial Manipulators.

Current methods for developing manipulator Jacobian matrices are based on traditional kinematic descriptions such as Denavit and Hartenberg parameters. The resulting symbolic equations for these matrices become cumbersome and computationally inefficient when dealing with more complex spatial manipulators, such as those seen in the field of biomechanics. This paper develops a modified method for Jacobian development based on generalized kinematic equations that incorporates partial derivatives of matrices with Leibniz's Law (the product rule). It is shown that a set of symbolic matrix functions can be derived that improve computational efficiency when used in MATLAB(®) M-Files and are applicable to any spatial manipulator. An articulated arm subassembly and a musculoskeletal model of the hand are used as examples.

The sensitivity of endpoint forces produced by the extrinsic muscles of the thumb to posture.

This study utilizes a biomechanical model of the thumb to estimate the force produced at the thumb-tip by each of the four extrinsic muscles. We used the principle of virtual work to relate joint torques produced by a given muscle force to the resulting endpoint force and compared the results to two separate cadaveric studies. When we calculated thumb-tip forces using the muscle forces and thumb postures described in the experimental studies, we observed large errors. When relatively small deviations from experimentally reported thumb joint angles were allowed, errors in force direction decreased substantially. For example, when thumb posture was constrained to fall within +/-15 degrees of reported joint angles, simulated force directions fell within experimental variability in the proximal-palmar plane for all four muscles. Increasing the solution space from +/-1 degrees to an unbounded space produced a sigmoidal decrease in error in force direction. Changes in thumb posture remained consistent with a lateral pinch posture, and were generally consistent with each muscle's function. Altering thumb posture alters both the components of the Jacobian and muscle moment arms in a nonlinear fashion, yielding a nonlinear change in thumb-tip force relative to muscle force. These results explain experimental data that suggest endpoint force is a nonlinear function of muscle force for the thumb, support the continued use of methods that implement linear transformations between muscle force and thumb-tip force for a specific posture, and suggest the feasibility of accurate prediction of lateral pinch force in situations where joint angles can be measured accurately.