title: Inferring muscle functional roles of the ostrich pelvic limb during walking and running using computer optimization.
abstract: Owing to their cursorial background, ostriches (Struthio camelus) walk and run with high metabolic economy, can reach very fast running speeds and quickly execute cutting manoeuvres. These capabilities are believed to be a result of their ability to coordinate muscles to take advantage of specialized passive limb structures. This study aimed to infer the functional roles of ostrich pelvic limb muscles during gait. Existing gait data were combined with a newly developed musculoskeletal model to generate simulations of ostrich walking and running that predict muscle excitations, force and mechanical work. Consistent with previous avian electromyography studies, predicted excitation patterns showed that individual muscles tended to be excited primarily during only stance or swing. Work and force estimates show that ostrich gaits are partially hip-driven with the bi-articular hip-knee muscles driving stance mechanics. Conversely, the knee extensors acted as brakes, absorbing energy. The digital extensors generated large amounts of both negative and positive mechanical work, with increased magnitudes during running, providing further evidence that ostriches make extensive use of tendinous elastic energy storage to improve economy. The simulations also highlight the need to carefully consider non-muscular soft tissues that may play a role in ostrich gait.
authors.affiliation: Structure and Motion Laboratory, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Hatfield, Herts, UK jrankin@rvc.ac.uk.
authors.forename: Jeffery W
authors.identifier: 0000-0002-6639-8280
authors.initials: JW
authors.lastname: Rankin
authors.affiliation: Department of Kinesiology, Pennsylvania State University, University Park, PA, USA School of Sport Science, Exercise and Health, The University of Western Australia, Perth, Western Australia, Australia.
authors.forename: Jonas
authors.initials: J
authors.lastname: Rubenson
authors.affiliation: Structure and Motion Laboratory, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Hatfield, Herts, UK.
authors.forename: John R
authors.identifier: 0000-0002-6767-7038
authors.initials: JR
authors.lastname: Hutchinson
mesh_terms: D000818:Animals; D003198:Computer Simulation; D006614:Hindlimb / Q000033:anatomy & histology / Q000502:physiology*; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D010388:Pelvis / Q000033:anatomy & histology / Q000502:physiology; D012420:Running / Q000502:physiology* / Q000523:psychology; D020310:Struthioniformes / Q000033:anatomy & histology / Q000502:physiology*; D016138:Walking / Q000502:physiology*
keywords: OpenSim; computed muscle control; forward dynamics; inverse dynamics; musculoskeletal model; static optimization