Recent literature on the public understanding of science has focused on replacing the deficit model of public communication in which experts disseminate information with one that encourages public participation and dialogue. Situated within this call for increased participation, this study looks at self-care practices in which medical expertise is not passively consumed by the layperson, but shared and (re)produced through arenas of lay practice. This collective knowledge production is facilitated by the online environment, which provides access to mediated medical knowledge and the ability to form communities in which users can negotiate this expertise and share their experiences. The laypersons examined here are members of the Canadian online collective, Running Mania, highlighting how this negotiation of expertise occurs in a “wellness” community. Drawing from member interviews and website observations of the site’s injury forum, the study examines collective injury management using two dominant theoretical discourses surrounding lay knowledge and participation in medical expertise: the lay expert whose knowledge arises from experience and the expert patient whose knowledge base parallels dominant biomedical discourse. Using the coproduction model and the related concepts of tinkering and logic of care from material semiotics, the research examines how these knowledge forms articulate to produce an intermediary discourse unique to this collective’s articulation of running and caring practices, a discourse that is enacted in individuals’ embodied negotiation of these multiple forms of medical expertise. It suggests that the logic of care has the potential to bridge the expert/lay boundary since the need for persistent, attentive tinkering applies across epistemological divides: in “good” care practices, multiple expertises are needed, both expert and lay, to hold the body together.Crown Copyright © 2021. Published by Elsevier Ltd. All rights reserved.