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We show that self-selected trunk leaning in humans aligns with minimized metabolic costs during running. Utilizing an integrative experimental and musculoskeletal simulation approach, we reveal how trunk leaning redistributes joint moments and metabolic demands. We report estimates of muscle-specific changes in metabolic demands and contraction conditions for key muscles, including the hamstrings, uniarticular hip extensors and plantar flexors, reflecting the complex interplay between kinetic demands and muscle energetics. Our results show that leaning forward reduces knee extension moments but involves metabolic cost trade-offs. Our findings indicate that the observed U-shaped whole-body metabolic cost curve is attributed to intricate and offsetting changes in metabolic cost among multiple muscle groups across trunk leaning conditions, reflecting the fundamental impact of trunk kinematics on running biomechanics.<\/jats:p>","DOI":"10.1098\/rspb.2025.2717","type":"journal-article","created":{"date-parts":[[2026,1,21]],"date-time":"2026-01-21T01:45:39Z","timestamp":1768959939000},"source":"Crossref","is-referenced-by-count":2,"title":["Humans choose trunk lean angles consistent with minimal metabolic costs\u2014an integrative experimental and musculoskeletal simulation approach"],"prefix":"10.1098","volume":"293","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5692-3785","authenticated-orcid":false,"given":"Luca","family":"Braun","sequence":"first","affiliation":[{"name":"Offenburg University 1 , ,","place":["77652 Offenburg, Germany"],"department":["Institute for Advanced Biomechanics and Motion Studies"]},{"name":"University of Michigan 2 , , ,","place":["Ann Arbor, MI 48109, USA"],"department":["School of Kinesiology"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Brian R.","family":"Umberger","sequence":"additional","affiliation":[{"name":"University of Michigan 2 , , ,","place":["Ann Arbor, MI 48109, USA"],"department":["School of Kinesiology"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Varun","family":"Joshi","sequence":"additional","affiliation":[{"name":"University of Michigan 2 , , ,","place":["Ann Arbor, MI 48109, USA"],"department":["School of Kinesiology"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yannick","family":"Denis","sequence":"additional","affiliation":[{"name":"Offenburg University 1 , ,","place":["77652 Offenburg, Germany"],"department":["Institute for Advanced Biomechanics and Motion Studies"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bastian","family":"Anedda","sequence":"additional","affiliation":[{"name":"Offenburg University 1 , ,","place":["77652 Offenburg, Germany"],"department":["Institute for Advanced Biomechanics and Motion Studies"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Steffen","family":"Willwacher","sequence":"additional","affiliation":[{"name":"Offenburg University 1 , ,","place":["77652 Offenburg, Germany"],"department":["Institute for Advanced Biomechanics and Motion Studies"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"175","published-online":{"date-parts":[[2026,1,21]]},"reference":[{"key":"2026012020453429400_R1","doi-asserted-by":"crossref","first-page":"1223","DOI":"10.1016\/0021-9290(95)00178-6","article-title":"Adjustments to Zatsiorsky-Seluyanov\u2019s segment inertia parameters","volume":"29","author":"de Leva","year":"1996","journal-title":"J. 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