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Using predictive gait simulations of the emu (\n                    <jats:italic>Dromaius novaehollandiae<\/jats:italic>\n                    ), we resolve this paradox by demonstrating that grounded running represents an optimal gait for birds, from both energetics and muscle excitations perspectives. Our virtual experiments decoupled effects of posture and tendon elasticity, biomechanically relevant anatomical features that cannot be isolated in real birds. The avian body plan prevents (near) vertical leg postures, making the running style used by humans impossible. Under this anatomical constraint, grounded running is optimal if the muscles produce the highest forces in crouched postures, as is true in most birds. Shared anatomical features suggest that, as a behavior, avian grounded running first evolved within non-avian dinosaurs.\n                  <\/jats:p>","DOI":"10.1126\/sciadv.ado0936","type":"journal-article","created":{"date-parts":[[2024,9,25]],"date-time":"2024-09-25T15:00:24Z","timestamp":1727276424000},"update-policy":"https:\/\/doi.org\/10.34133\/aaas_crossmark","source":"Crossref","is-referenced-by-count":16,"title":["Muscle-controlled physics simulations of bird locomotion resolve the grounded running paradox"],"prefix":"10.1126","volume":"10","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-5567-7022","authenticated-orcid":true,"given":"Pasha A.","family":"van Bijlert","sequence":"first","affiliation":[{"name":"Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Vening Meinesz Building A, Princetonlaan 8A, 3584 CB Utrecht, Netherlands."},{"name":"Naturalis Biodiversity Center, Darwinweg 2, 2333 CR Leiden, Netherlands."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1959-1061","authenticated-orcid":true,"given":"A. J.","family":"van Soest","sequence":"additional","affiliation":[{"name":"Department of Human Movement Sciences, Faculty of Behavioural and Movement Sciences, Vrije Universiteit Amsterdam, Van der Boechorststraat 7, 1081 BT Amsterdam, Netherlands."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9389-1540","authenticated-orcid":true,"given":"Anne S.","family":"Schulp","sequence":"additional","affiliation":[{"name":"Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Vening Meinesz Building A, Princetonlaan 8A, 3584 CB Utrecht, Netherlands."},{"name":"Naturalis Biodiversity Center, Darwinweg 2, 2333 CR Leiden, Netherlands."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0048-141X","authenticated-orcid":true,"given":"Karl T.","family":"Bates","sequence":"additional","affiliation":[{"name":"Department of Musculoskeletal and Ageing Science, Institute of Life Course &amp; Medical Sciences, University of Liverpool, The William Henry Duncan Building, 6 West Derby Street, Liverpool L7 8TX, UK."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"221","reference":[{"key":"e_1_3_2_2_2","unstructured":"R. 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