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Simulation of musculoskeletal systems using dynamic optimization is a powerful approach for studying the biomechanics of human movements and can be applied to human-robot interactions. The simulation results of human movements augmented by robotic devices may be used to evaluate and optimize the device design and controller. However, simulations are limited by the accuracy of the models which are usually simplified for computation efficiency. Typically, the powered robotic devices are often modeled as massless, ideal torque actuators that is without mass and internal dynamics, which may have significant impacts on the simulation results. This article investigates the effects of including the mass and internal dynamics of the device in simulations of assisted human movement. The device actuator was modeled in various ways with different detail levels. Dynamic optimization was used to find the muscle activations and actuator commands in motion tracking and predictive simulations. The results showed that while the effects of device mass and inertia can be small, the electrical dynamics of the motor can significantly impact the results. This outcome suggests the importance of using an accurate actuator model in simulations of human movement augmented by assistive devices. Novelty• Demonstrating the effects of including mass and internal dynamics of the actuator in simulations of assisted human movement • A new OpenSim electric motor actuator class to capture the electromechanical dynamics for use in simulation of human movement assisted by powered robotic devices

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Low back pain (LBP) has been associated with altered body sway during quiet standing, but the pattern of results is inconsistent. The purpose of this meta-analysis is to examine the effects of vision (eyes open, eyes closed) and changing the support surface (foam surface, firm surface) on postural sway during quiet standing in individuals with chronic LBP (cLBP). Five electronic databases were searched on March 27th, 2022. Of 2,856, 16 studies (n = 663) were included. Across all conditions, we found a positive and medium effect size (g = 0.77 [0.50, 1.04]) that represented greater body sway in individuals with cLBP. Subgroup analyses revealed medium effects during eyes open conditions (firm surface: g = 0.60 [0.33, 0.87]; foam surface: g = 0.68 [0.38, 0.97]), and large effects during eyes closed conditions (firm surface: g = 0.97 [0.60, 1.35]; foam surface: g = 0.89 [0.28, 1.51]). We quantified effects of self-reported pain and found a moderate effect during eyes closed plus firm surface conditions (Q = 3.28; p = 0.070). We conclude that cLBP is associated with increased postural sway, with largest effect sizes evident when vision is removed and when self-reported pain intensity is higher.

The acceptance of advanced prosthetic systems by users requires overcoming unique challenges of fitting prostheses to unique user anatomies to achieve systematic performance across a user base. Variations among individuals introduce complexities in fitting the sockets. Due to the difficulty of measuring socket interface characteristics, there is a lack of quantifiable diagnostic fitment information available. As a result, the process of fitting sockets is currently a laborintensive, manual approach, and can often result in sockets that are uncomfortable, unstable, or impede full range of motion. Additionally, results can be difficult to reproduce reliably. A diagnostic tool has been developed to quantify the relative movement between the socket and the residual bone during the fitting process. The approach leverages low cost and high precision ultrasound transceivers and intuitive visualization software to provide quantifiable socket fitment data. The goal is to enable a systematic socket-fitting strategy that yields reliable and reproducible results. Human subject testing and results are presented that show movement tracking relative to a cuff with an ultrasound transducer with an RMSD of 0.36 mm.