{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,11,14]],"date-time":"2026-11-14T03:26:15Z","timestamp":1794626775156,"version":"4.9.1"},"reference-count":25,"publisher":"Human Kinetics","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026]]},"abstract":"<jats:p>\n                    Natural ankle quasi-stiffness describes the joint\u2019s resistance to motion during loading in gait, which is informative for the design of biomimetic devices (eg,\u00a0prostheses, orthoses, and exoskeletons). Ankle quasi-stiffness is typically quantified as the slope of the moment\u2013angle curve using a linear approximation. Yet, recent studies during level-ground walking reveal that the human ankle displays a nonlinear behavior, in that the ankle stiffens with greater dorsiflexion. However, little is known regarding the nonlinear behavior when walking on slopes. Here, we aimed to quantify natural ankle quasi-stiffness during level and sloped walking. Twelve healthy young adults walked barefoot on an instrumented treadmill at 1.25\u00a0m\/s at 5 slopes: decline (\u221210\u00b0, \u22125\u00b0), level (0\u00b0), and incline (5\u00b0, 10\u00b0). Linear, quadratic, and cubic polynomial regressions were computed on ankle moment\u2013angle data during the loading phase. Adjusted\n                    <jats:italic>R<\/jats:italic>\n                    <jats:sup>2<\/jats:sup>\n                    values evaluated the goodness of fit. During the decline and level conditions, cubic regression best predicted the moment\u2013angle relationship (adjusted\n                    <jats:italic>R<\/jats:italic>\n                    <jats:sup>2<\/jats:sup>\n                    \u2009&gt;\u2009.975). During inclines, quadratic models best predicted the moment\u2013angle relationship, although the goodness of fit was low (adjusted\n                    <jats:italic>R<\/jats:italic>\n                    <jats:sup>2<\/jats:sup>\n                    \u2009&lt;\u2009.444). Such models were especially poor for the incline 10\u00b0 condition, revealing that a spring-like measure of ankle quasi-stiffness is not a sufficient summary for the ankle\u2019s behavior on steep inclines. Our results suggest that the human ankle exhibits nonlinear quasi-stiffness across level and sloped walking, with decline and level conditions being quantifiable by polynomial regression models. These findings may inform the design of biomimetic devices that can adapt to varying terrain.\n                  <\/jats:p>","DOI":"10.1123\/jab.2026-0017","type":"journal-article","created":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T15:22:51Z","timestamp":1788967371000},"page":"1-5","source":"Crossref","is-referenced-by-count":0,"title":["Quantifying Nonlinear Ankle Quasi-Stiffness During Level and Sloped Walking"],"prefix":"10.1123","author":[{"given":"Emma R.","family":"Caringella","sequence":"first","affiliation":[{"name":"Department of Health and Kinesiology, The University of Utah, Salt Lake City, UT, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8943-9639","authenticated-orcid":true,"given":"Kota Z.","family":"Takahashi","sequence":"additional","affiliation":[{"name":"Department of Health and Kinesiology, The University of Utah, Salt Lake City, UT, USA"},{"name":"Department of Physical Medicine & Rehabilitation, The University of Utah, Salt Lake City, UT, USA"},{"name":"Department of Biomedical Engineering, The University of Utah, Salt Lake City, UT, USA"},{"name":"Department of Mechanical Engineering, The University of Utah, Salt Lake City, UT, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"100","reference":[{"key":"r1","series-title":"J Biomech","doi-asserted-by":"publisher","DOI":"10.1016\/j.jbiomech.2025.112851","article-title":"Individual muscle contributions to lower-limb joint quasi-stiffness during steady-state healthy walking","volume":"190","author":"Molitor SL","year":"2025","unstructured":"Molitor SL, Neptune RR. Individual muscle contributions to lower-limb joint quasi-stiffness during steady-state healthy walking. J Biomech. 2025;190:112851. doi:10.1016\/j.jbiomech.2025.112851"},{"issue":"6","key":"r2","series-title":"Hum Mov Sci","doi-asserted-by":"publisher","first-page":"1185","DOI":"10.1016\/j.humov.2011.02.009","article-title":"Dynamics of the ankle joint analyzed through moment\u2013angle loops during human walking: gender and age effects","volume":"30","author":"Crenna P","year":"2011","unstructured":"Crenna P, Frigo C. Dynamics of the ankle joint analyzed through moment\u2013angle loops during human walking: gender and age effects. 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