Neuromusculoskeletal model that walks and runs across a speed range with a few motor control parameter changes based on the muscle synergy hypothesis

Shinya Aoi,Yury Ivanenko,Daiki Tamura,Ryoko Bamba,Soichiro Fujiki,Kei Senda,Tetsuro Funato,Tomohiro Ohashi,Kazuo Tsuchiya

doi:10.1038/s41598-018-37460-3

Shinya Aoi, Yury Ivanenko + Show 7 more

Open Access

https://doi.org/10.1038/s41598-018-37460-3

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Abstract

Humans walk and run, as well as change their gait speed, through the control of their complicated and redundant musculoskeletal system. These gaits exhibit different locomotor behaviors, such as a double-stance phase in walking and flight phase in running. The complex and redundant nature of the musculoskeletal system and the wide variation in locomotion characteristics lead us to imagine that the motor control strategies for these gaits, which remain unclear, are extremely complex and differ from one another. It has been previously proposed that muscle activations may be generated by linearly combining a small set of basic pulses produced by central pattern generators (muscle synergy hypothesis). This control scheme is simple and thought to be shared between walking and running at different speeds. Demonstrating that this control scheme can generate walking and running and change the speed is critical, as bipedal locomotion is dynamically challenging. Here, we provide such a demonstration by using a motor control model with 69 parameters developed based on the muscle synergy hypothesis. Specifically, we show that it produces both walking and running of a human musculoskeletal model by changing only seven key motor control parameters. Furthermore, we show that the model can walk and run at different speeds by changing only the same seven parameters based on the desired speed. These findings will improve our understanding of human motor control in locomotion and provide guiding principles for the control design of wearable exoskeletons and prostheses.

Highlights

Humans walk and run in accordance with the desired speed and circumstances
The motor control model consists of two components: one is the movement generator, which produces five weighted activation pulses in a feedforward fashion based on the muscle synergy hypothesis (Fig. 2B,C), and the other is the movement regulator, which regulates the locomotion movement in a feedback fashion based on somatosensory information with transmission delay
The musculoskeletal model changed the speed of each gait by changing only the same seven parameters based on the desired speed

Summary

Introduction

Humans walk and run in accordance with the desired speed and circumstances. These gaits have different characteristics at the kinematic level. This phase shift appears to change the running speed[14] These findings suggest that five activation pulses produce a large portion of motor commands in human walking and running and that the generation timing of the second pulse plays an important role in determining the gait and speed (Fig. 1B). This physiological hypothesis implies that the major motor control structure is simple and shared and that the difference between the gaits and speeds can be explained by a few components. Their model had about 20 parameters and changed the walking speed from 0.8 to 1.1 m/s in a two-dimensional musculoskeletal model by changing the stretch reflex feedback gain and trunk reference angle

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