{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,31]],"date-time":"2026-10-31T10:54:23Z","timestamp":1793444063256,"version":"4.5.0"},"reference-count":40,"publisher":"Public Library of Science (PLoS)","issue":"1","license":[{"start":{"date-parts":[[2025,1,17]],"date-time":"2025-01-17T00:00:00Z","timestamp":1737072000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS ONE"],"abstract":"<jats:p>Knee exoskeletons have been developed to assist, stabilize, or improve human movement or recovery. However, exoskeleton designers must implement transparency (i.e., get out of the way) modes during the swing phase of locomotor tasks to avoid impeding movement. The problem is that it is not understood how sensitive people are to small knee torques or what level of knee impedance is acceptable (sufficiently transparent) during swing phase. Here, we (i) characterized the biomechanical consequences of knee stiffness and damping during swing, and (ii) leveraged user perceptions of being impeded and toe clearance to define transparency thresholds, below which the participants were sufficiently unimpeded during the swing phase of gait. We conducted a series of human subject experiments that involved walking and stair ascent\/descent while wearing a modified knee brace with five stiffness values ranging from 0 to 4 Nm\/rad and five damping values ranging from 0 to 0.77 Nm\/rad\/s. We measured changes to lower limb kinematics, knee flexor muscle activity, and participants\u2019 perception of being impeded during swing. Kinematics, muscle activity, and perceived impedance all changed in response to added stiffness and damping. For stiffness, we found the median transparency thresholds for walking and stairs to be 1.76 Nm\/rad and 2.95 Nm\/rad, respectively, which corresponds to peak knee moments during swing of around 2.3 and 5 Nm. For damping, we found the median transparency threshold for walking and stairs to be about the same, 0.29 Nm\/rad\/s, which corresponds to peak knee moments during swing of around 2.3 Nm. These values provide useful benchmarks for defining quantitative design requirements for knee exoskeletons intended for locomotor activities.<\/jats:p>","DOI":"10.1371\/journal.pone.0317259","type":"journal-article","created":{"date-parts":[[2025,1,17]],"date-time":"2025-01-17T19:58:26Z","timestamp":1737143906000},"page":"e0317259","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":3,"title":["Establishing thresholds for swing transparency at the knee during gait to inform exoskeleton design"],"prefix":"10.1371","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0183-6358","authenticated-orcid":true,"given":"Chase W.","family":"Mathews","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0009-3064-2534","authenticated-orcid":true,"given":"Delaney A.","family":"Clawson","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Karl E.","family":"Zelik","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"340","published-online":{"date-parts":[[2025,1,17]]},"reference":[{"issue":"2","key":"pone.0317259.ref001","doi-asserted-by":"crossref","first-page":"110","DOI":"10.1034\/j.1600-0838.2001.011002110.x","article-title":"Is a knee brace advantageous after anterior cruciate ligament surgery?","volume":"11","author":"S Brandsson","year":"2001","journal-title":"Scandinavian Journal of Medicine & Science in Sports"},{"issue":"9","key":"pone.0317259.ref002","doi-asserted-by":"crossref","first-page":"1925","DOI":"10.1002\/jor.25556","article-title":"Tricompartment offloader knee brace reduces contact forces in adults with multicompartment knee osteoarthritis","volume":"41","author":"EL Bishop","year":"2023","journal-title":"Journal of Orthopaedic Research"},{"key":"pone.0317259.ref003","doi-asserted-by":"crossref","first-page":"937","DOI":"10.2165\/11317790-000000000-00000","article-title":"The potential role of prophylactic\/functional knee bracing in preventing knee ligament injury","volume":"39","author":"N Rishiraj","year":"2009","journal-title":"Sports Medicine"},{"key":"pone.0317259.ref004","doi-asserted-by":"crossref","unstructured":"Elliott G, Sawicki GS, Marecki A, Herr H. The biomechanics and energetics of human running using an elastic knee exoskeleton. In: 2013 IEEE 13th International Conference on Rehabilitation Robotics (ICORR); 2013. p. 1\u20136.","DOI":"10.1109\/ICORR.2013.6650418"},{"issue":"6","key":"pone.0317259.ref005","doi-asserted-by":"crossref","first-page":"065027","DOI":"10.1088\/1361-665X\/aa6cec","article-title":"A knee-mounted biomechanical energy harvester with enhanced efficiency and safety","volume":"26","author":"C Chen","year":"2017","journal-title":"Smart Materials and Structures"},{"key":"pone.0317259.ref006","doi-asserted-by":"crossref","unstructured":"Shamaei K, Dollar AM. On the mechanics of the knee during the stance phase of the gait. 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A quasi-passive compliant stance control Knee-Ankle-Foot Orthosis. 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