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Natural experiments have been able to demonstrate that marathons are completed close to, but below, critical speed and that faster athletes complete marathons at a higher fraction of critical speed compared with slower runners. Environmental conditions, such as heat and altitude, as well as training and racing behaviors, including the characteristics of training programs and pacing strategies, have also been demonstrated to impact marathon performance. Findings from the natural experiments discussed herein often align with results from smaller, laboratory-controlled studies. However, the scale of these datasets has allowed for the detection of subtle trends and interactions that otherwise would remain undetected in smaller cohorts. In conclusion, natural experiments have helped advance our understanding of marathon physiology and can effectively complement traditional laboratory-based interventions. Future research may explore hybrid approaches in which researchers conducting well-controlled laboratory experiments collaborate with running platforms to design integrated research studies that combine large sample sizes with laboratory-controlled interventions.<\/jats:p>","DOI":"10.1152\/japplphysiol.00792.2025","type":"journal-article","created":{"date-parts":[[2026,8,10]],"date-time":"2026-08-10T03:54:13Z","timestamp":1786334053000},"page":"813-820","update-policy":"https:\/\/doi.org\/10.1152\/aps-crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Natural experiments in marathon running"],"prefix":"10.1152","volume":"141","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6748-9870","authenticated-orcid":false,"given":"Daniel","family":"Muniz-Pumares","sequence":"first","affiliation":[{"name":"University of Hertfordshire","place":["United Kingdom"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2329-959X","authenticated-orcid":false,"given":"Ed","family":"Maunder","sequence":"additional","affiliation":[{"name":"Auckland University of Technology","place":["New Zealand"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Barry","family":"Smyth","sequence":"additional","affiliation":[{"name":"University College Dublin","place":["Ireland"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4190-4543","authenticated-orcid":false,"given":"Ben","family":"Hunter","sequence":"additional","affiliation":[{"name":"London Metropolitan University","place":["United Kingdom"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"24","reference":[{"key":"B1","doi-asserted-by":"publisher","DOI":"10.1002\/CPHY.C220027"},{"key":"B2","doi-asserted-by":"publisher","DOI":"10.1249\/MSS.0B013E318213FEFB"},{"key":"B3","doi-asserted-by":"publisher","DOI":"10.1038\/NATURE03052"},{"key":"B4","unstructured":"Sayer A. 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