{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,22]],"date-time":"2026-06-22T10:09:06Z","timestamp":1782122946517,"version":"3.54.5"},"reference-count":45,"publisher":"Wiley","issue":"5","license":[{"start":{"date-parts":[[2023,7,11]],"date-time":"2023-07-11T00:00:00Z","timestamp":1689033600000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001720","name":"Nutricia Research Foundation","doi-asserted-by":"publisher","award":["2019\u201030"],"award-info":[{"award-number":["2019\u201030"]}],"id":[{"id":"10.13039\/501100001720","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["J cachexia sarcopenia muscle"],"published-print":{"date-parts":[[2023,10]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:sec><jats:title>Background<\/jats:title><jats:p>The decline in postabsorptive and postprandial muscle protein fractional synthesis rates (FSR) does not quantitatively account for muscle atrophy during uncomplicated, short\u2010term disuse, when atrophy rates are the highest. We sought to determine whether 2\u00a0days of unilateral knee immobilization affects mixed muscle protein fractional breakdown rates (FBR) during postabsorptive and simulated postprandial conditions.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>Twenty\u2010three healthy, male participants (age: 22\u00a0\u00b1\u00a01\u00a0year; height: 179\u00a0\u00b1\u00a01\u00a0cm; body mass: 73.4\u00a0\u00b1\u00a01.5\u00a0kg; body mass index 22.8\u00a0\u00b1\u00a00.5\u00a0kg\u00b7m<jats:sup>\u22122<\/jats:sup>) took part in this randomized, controlled study. After 48\u00a0h of unilateral knee immobilization, primed continuous intravenous <jats:sc>l<\/jats:sc>\u2010[<jats:sup>15<\/jats:sup>N]\u2010phenylalanine and <jats:sc>l<\/jats:sc>\u2010[<jats:italic>ring<\/jats:italic>\u2010<jats:sup>2<\/jats:sup>H<jats:sub>5<\/jats:sub>]\u2010phenylalanine infusions were used for parallel determinations of FBR and FSR, respectively, in a postabsorptive (saline infusion; FAST) or simulated postprandial state (67.5\u00a0mg\u00b7kg body mass<jats:sup>\u22121<\/jats:sup>\u00b7h<jats:sup>\u22121<\/jats:sup> amino acid infusion; FED). Bilateral <jats:italic>m. vastus lateralis<\/jats:italic> biopsies from the control (CON) and immobilized (IMM) legs, and arterialized\u2010venous blood samples, were collected throughout.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Amino acid infusion rapidly increased plasma phenylalanine (59\u00a0\u00b1\u00a09%), leucine (76\u00a0\u00b1\u00a05%), isoleucine (109\u00a0\u00b1\u00a07%) and valine (42\u00a0\u00b1\u00a04%) concentrations in FED only (all <jats:italic>P<\/jats:italic>\u00a0&lt;\u00a00.001), which was sustained for the remainder of infusion. Serum insulin concentrations peaked at 21.8\u00a0\u00b1\u00a02.2\u00a0mU\u00b7L<jats:sup>\u22121<\/jats:sup> at 15\u00a0min in FED only (<jats:italic>P<\/jats:italic>\u00a0&lt;\u00a00.001) and were 60% greater in FED than FAST (<jats:italic>P<\/jats:italic>\u00a0&lt;\u00a00.01). Immobilization did not influence FBR in either FAST (CON: 0.150\u00a0\u00b1\u00a00.018; IMM: 0.143\u00a0\u00b1\u00a00.017%\u00b7h<jats:sup>\u22121<\/jats:sup>) or FED (CON: 0.134\u00a0\u00b1\u00a00.012; IMM: 0.160\u00a0\u00b1\u00a00.018%\u00b7h<jats:sup>\u22121<\/jats:sup>; all effects <jats:italic>P<\/jats:italic>\u00a0&gt;\u00a00.05). However, immobilization decreased FSR (<jats:italic>P<\/jats:italic>\u00a0&lt;\u00a00.05) in both FAST (0.071\u00a0\u00b1\u00a00.004 vs. 0.086\u00a0\u00b1\u00a00.007%\u00b7h<jats:sup>\u22121<\/jats:sup>; IMM vs CON, respectively) and FED (0.066\u00a0\u00b1\u00a00.016 vs. 0.119\u00a0\u00b1\u00a00.016%\u00b7h<jats:sup>\u22121<\/jats:sup>; IMM vs CON, respectively). Consequently, immobilization decreased net muscle protein balance (<jats:italic>P<\/jats:italic>\u00a0&lt;\u00a00.05) and to a greater extent in FED (CON: \u22120.012\u00a0\u00b1\u00a00.025; IMM: \u22120.095\u00a0\u00b1\u00a00.023%\u00b7h<jats:sup>\u22121<\/jats:sup>; <jats:italic>P<\/jats:italic>\u00a0&lt;\u00a00.05) than FAST (CON: \u22120.064\u00a0\u00b1\u00a00.020; IMM: \u22120.072\u00a0\u00b1\u00a00.017%\u00b7h<jats:sup>\u22121<\/jats:sup>).<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>We conclude that merely 2\u00a0days of leg immobilization does not modulate postabsorptive and simulated postprandial muscle protein breakdown rates. Instead, under these conditions the muscle negative muscle protein balance associated with brief periods of experimental disuse is driven near exclusively by reduced basal muscle protein synthesis rates and anabolic resistance to amino acid administration.<\/jats:p><\/jats:sec>","DOI":"10.1002\/jcsm.13284","type":"journal-article","created":{"date-parts":[[2023,7,11]],"date-time":"2023-07-11T09:30:00Z","timestamp":1689067800000},"page":"2064-2075","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":18,"title":["Short\u2010term disuse does not affect postabsorptive or postprandial muscle protein fractional breakdown rates"],"prefix":"10.1002","volume":"14","author":[{"given":"George F.","family":"Pavis","sequence":"first","affiliation":[{"name":"Nutritional Physiology Research Group, Public Health &amp; Sport Sciences, Faculty of Health and Life Sciences University of Exeter  Exeter UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Doaa R.","family":"Abdelrahman","sequence":"additional","affiliation":[{"name":"Department of Surgery University of Texas Medical Branch  Galveston TX USA"},{"name":"Sealy Center of Aging University of Texas Medical Branch  Galveston TX USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Andrew J.","family":"Murton","sequence":"additional","affiliation":[{"name":"Department of Surgery University of Texas Medical Branch  Galveston TX USA"},{"name":"Sealy Center of Aging University of Texas Medical Branch  Galveston TX USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Benjamin T.","family":"Wall","sequence":"additional","affiliation":[{"name":"Nutritional Physiology Research Group, Public Health &amp; Sport Sciences, Faculty of Health and Life Sciences University of Exeter  Exeter UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Francis 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