title: Modular control of human walking: a simulation study.
abstract: Recent evidence suggests that performance of complex locomotor tasks such as walking may be accomplished using a simple underlying organization of co-active muscles, or "modules", which have been assumed to be structured to perform task-specific biomechanical functions. However, no study has explicitly tested whether the modules would actually produce the biomechanical functions associated with them or even produce a well-coordinated movement. In this study, we generated muscle-actuated forward dynamics simulations of normal walking using muscle activation modules (identified using non-negative matrix factorization) as the muscle control inputs to identify the contributions of each module to the biomechanical sub-tasks of walking (i.e., body support, forward propulsion, and leg swing). The simulation analysis showed that a simple neural control strategy involving five muscle activation modules was sufficient to perform the basic sub-tasks of walking. Module 1 (gluteus medius, vasti, and rectus femoris) primarily contributed to body support in early stance while Module 2 (soleus and gastrocnemius) contributed to both body support and propulsion in late stance. Module 3 (rectus femoris and tibialis anterior) acted to decelerate the leg in early and late swing while generating energy to the trunk throughout swing. Module 4 (hamstrings) acted to absorb leg energy (i.e., decelerate it) in late swing while increasing the leg energy in early stance. Post-hoc analysis revealed an additional module (Module 5: iliopsoas) acted to accelerate the leg forward in pre- and early swing. These results provide evidence that the identified modules can act as basic neural control elements that generate task-specific biomechanical functions to produce well-coordinated walking.
authors.affiliation: Department of Mechanical Engineering, University of Texas at Austin, 1 University Station C2200, Austin, TX 78712, USA. rneptune@mail.utexas.edu
authors.forename: Richard R
authors.initials: RR
authors.lastname: Neptune
authors.forename: David J
authors.initials: DJ
authors.lastname: Clark
authors.forename: Steven A
authors.initials: SA
authors.lastname: Kautz
mesh_terms: D001696:Biomechanical Phenomena; D003198:Computer Simulation; D006801:Humans; D008954:Models, Biological; D009142:Musculoskeletal Physiological Phenomena; D016138:Walking / Q000502:physiology*