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We examined the effects of a multi-ingredient supplement containing fish protein, vitamin D, and \u03c93 fatty acids, taken during HIFT, on physical performance in trained individuals.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>Twenty-five recreationally trained participants (14 females, 11 males) underwent 6\u00a0weeks of HIFT (3 times\/week) while taking each of three supplements, separated by 2-week washout periods in a researcher-blinded, randomized, triple-crossover, and counterbalanced fashion. The supplements and daily doses were (a) 0.6\u00a0g fish protein\/kg body mass, 21\u00a0\u03bcg vitamin D, and 1.8\u00a0g \u03c93 fatty acids [including 1.4\u00a0g eicosapentaenoic (EPA) and docosahexaenoic acid (DHA)], (b) 0.6\u00a0g\/kg whey protein, and (c) 0.6\u00a0g\/kg maltodextrin. Participants followed isoenergetic diets providing 1.0\u00a0g protein\/kg body mass, 30\u00a0\u03bcg vitamin D, and 0.2\u00a0g EPA and DHA daily. Training variables were assessed during the 1st and 6th weeks of each intervention period. Endurance and strength variables were measured before and after each intervention period. Data were analyzed using 2-way repeated-measure ANOVA (supplement\u2009\u00d7\u2009training).<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      HIFT augmented workout duration per training session (\n                      <jats:italic>p<\/jats:italic>\n                      \u2009=\u20090.007). One-repetition maximum and maximal force of shoulder press, as well as strength endurance of core muscles, increased by 3\u20136% with training (\n                      <jats:italic>p<\/jats:italic>\n                      \u2009&lt;\u20090.001). Supplementation did not affect any of these adaptations.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>Six weeks of HIFT improved some training and performance variables in recreationally trained adults. However, increasing the intake of protein, vitamin D, and \u03c93 fatty acids did not influence the variables assessed.<\/jats:p>\n                    <jats:p>Trial Registation Number: NCT05402527 (22\/4\/2022), clinicaltrials.gov.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1007\/s00394-026-03983-z","type":"journal-article","created":{"date-parts":[[2026,5,26]],"date-time":"2026-05-26T15:03:54Z","timestamp":1779807834000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Effects of a nutritional supplement containing fish protein, vitamin D, and \u03c93 fatty acids, taken during high-intensity functional training, on physical performance in recreationally trained individuals: a randomized controlled trial"],"prefix":"10.1007","volume":"65","clinical-trial-number":[{"clinical-trial-number":"nct05402527","registry":"10.18810\/clinical-trials-gov"}],"author":[{"ORCID":"https:\/\/orcid.org\/0009-0001-1623-4392","authenticated-orcid":false,"given":"Ioannis","family":"Kosmidis","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0005-7728-4317","authenticated-orcid":false,"given":"Christina","family":"Karpouzi","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5060-1950","authenticated-orcid":false,"given":"Anatoli","family":"Petridou","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gabriela","family":"Voulgaridou","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3382-0438","authenticated-orcid":false,"given":"Gregory C.","family":"Bogdanis","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8430-7231","authenticated-orcid":false,"given":"Vassilis","family":"Mougios","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,5,26]]},"reference":[{"issue":"12","key":"3983_CR1","doi-asserted-by":"publisher","DOI":"10.1371\/journal.pone.0295531","volume":"18","author":"X Wang","year":"2023","unstructured":"Wang X, Soh KG, Samsudin S et al (2023) Effects of high-intensity functional training on physical fitness and sport-specific performance among the athletes: a systematic review with meta-analysis. 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