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Under isoflurane anesthesia, fatigue was induced in rat soleus muscles in situ by isotonic shortening contractions at 37\u00b0C. Muscles were stimulated repeatedly for 1 s at 30 Hz every 2 s for a total of 15 min. The muscles were allowed to shorten isotonically against a load corresponding to one-third of maximal isometric force. Maximal unloaded shortening velocity (V<jats:sub>0<\/jats:sub>), maximum force production (F<jats:sub>max<\/jats:sub>), and isometric relaxation rate (\u2212dF\/d t) was reduced after 100 s but returned to almost initial values at the end of the stimulation protocol. Likewise, ATP and creatine phosphate (CrP) were reduced after 100 s, but the level of CrP was partially restored to initial values after 15 min. The rate of isometric force development, the velocity of shortening, and isotonic shortening were also reduced at 100 s, but in striking contrast, did not recover during the remainder of the stimulation protocol. The regulatory myosin light chain (MLC2s) was dephosphorylated after 100 s and did not recover. Although metabolic changes may account for the changes of F<jats:sub>max<\/jats:sub>, \u2212dF\/d t, and V<jats:sub>0<\/jats:sub>, dephosphorylation of MLC2s may be involved in the fatigue seen as sustained slower contraction velocities and decreased muscle shortening.<\/jats:p>","DOI":"10.1152\/ajpregu.91043.2008","type":"journal-article","created":{"date-parts":[[2009,7,23]],"date-time":"2009-07-23T02:23:14Z","timestamp":1248315794000},"page":"R900-R910","source":"Crossref","is-referenced-by-count":18,"title":["Causes of fatigue in slow-twitch rat skeletal muscle during dynamic activity"],"prefix":"10.1152","volume":"297","author":[{"given":"Morten","family":"Munkvik","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Per Kristian","family":"Lunde","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ole M.","family":"Sejersted","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"24","reference":[{"key":"R1","doi-asserted-by":"publisher","DOI":"10.1152\/physrev.00015.2007"},{"key":"R2","doi-asserted-by":"publisher","DOI":"10.1152\/jappl.1992.73.5.2105"},{"key":"R3","doi-asserted-by":"publisher","DOI":"10.1152\/jappl.1990.69.2.740"},{"key":"R4","doi-asserted-by":"publisher","DOI":"10.1007\/BF00634377"},{"key":"R5","doi-asserted-by":"publisher","DOI":"10.1111\/j.1365-201X.2004.01338.x"},{"key":"R6","doi-asserted-by":"crossref","unstructured":"Bigland-Ritchie B.Muscle fatigue and the influence of changing neural drive.Clin Chest Med5: 21\u201334, 1984.","DOI":"10.1016\/S0272-5231(21)00229-X"},{"key":"R7","doi-asserted-by":"publisher","DOI":"10.1002\/mus.20891"},{"key":"R8","doi-asserted-by":"publisher","DOI":"10.1113\/expphysiol.1989.sp003367"},{"key":"R9","doi-asserted-by":"publisher","DOI":"10.1007\/BF00584493"},{"key":"R10","doi-asserted-by":"publisher","DOI":"10.1007\/s10439-008-9496-x"},{"key":"R11","doi-asserted-by":"crossref","unstructured":"Dudley GA, Tullson PC, Terjung RL.Influence of mitochondrial content on the sensitivity of respiratory control.J Biol Chem262: 9109\u20139114, 1987.","DOI":"10.1016\/S0021-9258(18)48054-4"},{"key":"R12","unstructured":"Edwards RH.Human muscle function and fatigue. 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