{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T21:00:25Z","timestamp":1788987625602,"version":"build-2803163510"},"reference-count":71,"publisher":"Springer Science and Business Media LLC","issue":"1","license":[{"start":{"date-parts":[[2025,11,21]],"date-time":"2025-11-21T00:00:00Z","timestamp":1763683200000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"},{"start":{"date-parts":[[2025,11,21]],"date-time":"2025-11-21T00:00:00Z","timestamp":1763683200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"}],"funder":[{"name":"Johannes Gutenberg-Universit\u00e4t Mainz"}],"content-domain":{"domain":["link.springer.com"],"crossmark-restriction":false},"short-container-title":["Sports Med - Open"],"abstract":"Abstract<\/jats:title>\n \n Background<\/jats:title>\n \n This study aimed to evaluate acute and chronic exercise-induced changes in cell-free DNA (cfDNA) concentrations during a 7-day high-intensity interval training (HIIT) shock microcycle in trained endurance athletes. Thirty-five participants were randomly assigned to one of three groups: a HIIT-only group (HSM), a HIIT plus low-intensity training group (HSM\u2009+\u2009LIT), and a control group maintaining regular training. The intervention included 10 HIIT sessions (5\u2009\u00d7\u20094\u00a0min at 90\u201395% maximum heart rate) over 7 days, with HSM\u2009+\u2009LIT completing an additional 30\u00a0min of low-intensity training after each session. Physiological exercise testing (PET) was conducted at baseline, 3-, 7-, and 14-days post-intervention. On days 2 and 7 during the intervention, HIIT sessions were supervised in both morning and afternoon, and venous blood samples were collected at rest, immediately post-exercise, and 30\u00a0min post-exercise to measure cfDNA for 90 and 222\u00a0bp fragments. Correlations between cfDNA and physiological exercise variables such as peak power output (PPO), running velocity at lactate threshold (LT), and VO\u2082\n max<\/jats:sub>\n were analyzed.\n <\/jats:p>\n <\/jats:sec>\n \n Results<\/jats:title>\n \n cfDNA\n 90<\/jats:sup>\n (10.4-fold,\n p<\/jats:italic>\n \u2009<\u20090.001) and cfDNA\n 222<\/jats:sup>\n (12.4-fold,\n p<\/jats:italic>\n \u2009<\u20090.001) increased significantly after PET. In addition, cfDNA\n 90<\/jats:sup>\n (17.1-fold,\n p<\/jats:italic>\n \u2009<\u20090.001) and cfDNA\n 222<\/jats:sup>\n (20.2-fold,\n p<\/jats:italic>\n \u2009<\u20090.001) increased after HIIT, both remaining significantly elevated 30\u00a0min post-HIIT (both\n p<\/jats:italic>\n \u2009<\u20090.001). cfDNA\n 90<\/jats:sup>\n concentrations were higher in afternoon (22.4-fold) compared to morning HIIT sessions (17.2-fold,\n p<\/jats:italic>\n \u2009<\u20090.001). A significant interaction effect was found between group and measurement point for cfDNA\n 90<\/jats:sup>\n (\n p<\/jats:italic>\n \u2009<\u20090.001) and cfDNA\n 222<\/jats:sup>\n (\n p<\/jats:italic>\n \u2009<\u20090.001), with higher concentrations in HSM\u2009+\u2009LIT compared to HSM 30\u00a0min post-HIIT. cfDNA\n 90<\/jats:sup>\n showed moderate correlations with PPO (\n r<\/jats:italic>\n \u2009=\u20090.48,\n p<\/jats:italic>\n \u2009<\u20090.001), LT (\n r<\/jats:italic>\n \u2009=\u20090.36,\n p<\/jats:italic>\n \u2009<\u20090.001) and VO\n \u2082max<\/jats:sub>\n (\n r<\/jats:italic>\n \u2009=\u20090.30,\n p<\/jats:italic>\n \u2009=\u20090.01). cfDNA\n 222<\/jats:sup>\n correlated moderately with VO\n \u2082max<\/jats:sub>\n (\n r<\/jats:italic>\n \u2009=\u20090.34,\n p<\/jats:italic>\n \u2009=\u20090.001) and slightly with PPO (\n r<\/jats:italic>\n \u2009=\u20090.21,\n p<\/jats:italic>\n \u2009=\u20090.05). No chronic changes in cfDNA were observed throughout the study period.\n <\/jats:p>\n <\/jats:sec>\n \n Conclusions<\/jats:title>\n cfDNA is a reliable marker for detecting acute exercise-induced stress. However, the potential of cfDNA for detecting chronic adaptations in short-term, high-intensity interval training settings, such as a HIIT shock cycle, appears limited thus far.<\/jats:p>\n \n Trial registration<\/jats:italic>\n clinicaltrials.gov, NCT05067426. Registered 05 October 2021\u2014Retrospectively registered,\n https:\/\/clinicaltrials.gov\/ct2\/show\/NCT05067426<\/jats:ext-link>\n .\n <\/jats:p>\n <\/jats:sec>\n \n Graphical Abstract<\/jats:title>\n <\/jats:sec>","DOI":"10.1186\/s40798-025-00923-9","type":"journal-article","created":{"date-parts":[[2025,11,21]],"date-time":"2025-11-21T13:43:30Z","timestamp":1763732610000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Acute and Chronic Effects of a High-Intensity Interval Training Shock Microcycle on Cell-Free DNA: A Randomized Controlled Trial"],"prefix":"10.1186","volume":"11","author":[{"given":"Aleksandar","family":"Tomaskovic","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tilmann","family":"Strepp","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thomas Leonhard","family":"St\u00f6ggl","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elmo W. 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Both verbal and written consent was obtained from all study participants for this study. The study was conducted in accordance with the Declaration of Helsinki. Note that Blumkaitis et al. [\n \n ] published a small subset of cfDNA data from the first physiological exercise testing (T1), while the data from the intervention and post-intervention periods are entirely new. Selected physiological exercise variables used for correlation analyses in the present study were previously published by Strepp et al. [\n \n ].","order":2,"name":"Ethics","group":{"name":"EthicsHeading","label":"Ethics Approval and Consent to Participate"}},{"value":"Not applicable.","order":3,"name":"Ethics","group":{"name":"EthicsHeading","label":"Consent for Publication"}},{"value":"Aleksandar Tomaskovic, Tilmann Strepp, Thomas Leonhard St\u00f6ggl, Elmo W. I. Neuberger, Perikles Simon, and Nils Haller declare that they have no competing interests.","order":4,"name":"Ethics","group":{"name":"EthicsHeading","label":"Competing Interests"}}],"article-number":"132"}}