Muscles actuate movement by generating forces. The forces generated by muscles are highly dependent on their ﬁbre lengths, yet it is difﬁcult to measure the lengths over which muscle ﬁbres operate during movement. We combined experimental measurements of joint angles and muscle activation patterns during walking with a musculoskeletal model that captures the relationships between muscle ﬁbre lengths, joint angles and muscle activations for muscles of the lower limb. We used this musculoskeletal model to produce a simulation of muscle– tendon dynamics during walking and calculated ﬁbre operating lengths (i.e. the length of muscle ﬁbres relative to their optimal ﬁbre length) for 17 lower limb muscles. Our results indicate that when musculotendon compliance is low, the muscle ﬁbre operating length is determined predominantly by the joint angles and muscle moment arms. If musculotendon compliance is high, muscle ﬁbre operating length is more dependent on activation level and force– length– velocity effects. We found that muscles operate on multiple limbs of the force– length curve (i.e. ascending, plateau and descending limbs) during the gait cycle, but are active within a smaller portion of their total operating range.
Enable researchers to reproduce the results described in the paper.
The study associated with this project used a musculoskeletal model that describes the relationship between fiber lenght and joint angle to determine the fiber operating lengths of lower limb muscles during a typical gait cycle for a single subject, using literature values of muscle activation. This project contains the setup files, input data, simulation results, and intermediate programs used to find the results presented in the attached publications. These files include motion files for a single, averaged gait cycle, a scaled model, input muscle controls, OpenSim setup files, and several custom API programs used to add necessary functionality to the OpenSim workflow.