{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,19]],"date-time":"2026-02-19T15:58:07Z","timestamp":1771516687815,"version":"3.50.1"},"reference-count":23,"publisher":"Wiley","issue":"18","license":[{"start":{"date-parts":[[2025,9,21]],"date-time":"2025-09-21T00:00:00Z","timestamp":1758412800000},"content-version":"vor","delay-in-days":20,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["physoc.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Physiological Reports"],"published-print":{"date-parts":[[2025,9]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>This exploratory study examined the effects of varying frequencies of 4 \u00d7\u20094\u2010min high\u2010intensity interval training (HIIT) sessions (once, twice, or thrice weekly) on cardiorespiratory, metabolic, perceptual, and performance variables in recreationally active individuals. Twenty\u2010six participants (VO<jats:sub>2max<\/jats:sub>: 51.3\u2009\u00b1\u20097.1\u2009mL\u00b7kg<jats:sup>\u22121<\/jats:sup>\u00b7min<jats:sup>\u22121<\/jats:sup>) completed a six\u2010week intervention, utilizing individualized HIIT protocols based on maximal treadmill speed and heart rate. Pre\u2010 and post\u2010assessments involved an incremental treadmill test evaluating maximal oxygen uptake (VO<jats:sub>2max<\/jats:sub>), time to exhaustion (TTE), ventilatory threshold (VT<jats:sub>1<\/jats:sub>), submaximal heart rate, and running economy (i.e., submaximum oxygen uptake). Adherence rates ranged from 91% to 100%. Significant improvements in VO<jats:sub>2max<\/jats:sub> and TTE were observed across all training frequencies (<jats:italic>p<\/jats:italic>\u2009&lt;\u20090.05), with moderate\u2010to\u2010large effect sizes (Cohen's d [95% CI] for VO<jats:sub>2max<\/jats:sub>\u2009=\u20090.09\u20130.61 [\u22120.56 to 1.42]; TTE: 0.02\u20130.77 [\u22120.65 to 1.61]). The largest effects (<jats:italic>d<\/jats:italic>\u2009&gt;\u20090.5) were found for VO<jats:sub>2max<\/jats:sub> and TTE in the groups training two or three times per week. 2\u20133 weekly sessions of 4\u2009\u00d7\u20094\u2010min HIIT may be effective for improving VO<jats:sub>2max<\/jats:sub> and TTE in recreationally active individuals, with no clear additional benefit from increasing the frequency to three sessions per week. These preliminary findings highlight the potential of twice\u2010weekly HIIT as a practical and time\u2010efficient training strategy, while acknowledging limited precision.<\/jats:p>","DOI":"10.14814\/phy2.70573","type":"journal-article","created":{"date-parts":[[2025,9,22]],"date-time":"2025-09-22T05:37:39Z","timestamp":1758519459000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Impact of weekly frequency of high\u2010intensity interval training on cardiorespiratory, metabolic, and performance measures in recreational runners \u2013 An exploratory study"],"prefix":"10.14814","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0009-0001-5204-3569","authenticated-orcid":false,"given":"Mascha","family":"Lenk","sequence":"first","affiliation":[{"name":"Integrative and Experimental Exercise Science and Training, Department of Sport Science University of W\u00fcrzburg  W\u00fcrzburg Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Manuel","family":"Matzka","sequence":"additional","affiliation":[{"name":"Integrative and Experimental Exercise Science and Training, Department of Sport Science University of W\u00fcrzburg  W\u00fcrzburg Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Lukas","family":"Lauber","sequence":"additional","affiliation":[{"name":"Integrative and Experimental Exercise Science and Training, Department of Sport Science University of W\u00fcrzburg  W\u00fcrzburg Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Philipp","family":"Kunz","sequence":"additional","affiliation":[{"name":"Integrative and Experimental Exercise Science and Training, Department of Sport Science University of W\u00fcrzburg  W\u00fcrzburg Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Billy","family":"Sperlich","sequence":"additional","affiliation":[{"name":"Integrative and 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