Project Summary The goal of this supplement is to enable a large community of musculoskeletal modeling researchers to easily access and robustly use validated biophysical muscle models generated by the parent grant to generate multiscale simulations of muscle function. To date, there are extremely few musculoskeletal movement simulations (<5) that use biophysically-based muscle models; those that are available are not easily generalizable for use by other researchers. Research from the parent grant establishes new, experimentally- validated formulations of biophysical muscle models to reproduce novel features of muscle force generation for understanding sensorimotor function in behavioral and clinical contexts. We use the MyoSim software platform developed by Co-I Campbell to demonstrate the superiority of biophysical muscle models over standard phenomenological models used in musculoskeletal simulations of movement. However, it will be difficult for other researchers to easily implement these models in other movement contexts. This supplement will enable broader dissemination of our ongoing and prior research, to enhance open science and accelerate progress in multiscale modeling in the muscle, cardiac, and musculoskeletal modeling communities. Software Supplement Aim 1 will improve, standardize, and document MyoSim software so that it can be easily integrated with other multiscale simulations on scientific computing platforms such as MATLAB and Python. Software Supplement Aim 2 will integrate MyoSim muscle models with OpenSim, an NIH-funded musculoskeletal simulation platform with ~70,000 users. The supplement will also support virtual tutorial workshops aimed at muscle modeling researchers including muscle and cardiac researchers, including those using finite element models, and the OpenSim musculoskeletal modeling community. Creating open, generalizable and extensible MyoSim functionality for multiscale modeling will increase scientific innovation and enhance open science in musculoskeletal research, and dramatically increase the MyoSim user base.