Repeated high-intensity exercise modulates Ca(2+) sensitivity of human skeletal muscle fibers

K D Gejl, L G Hvid, S J Willis, E Andersson, H-C Holmberg, Rasmus Jensen, U Frandsen, J Hansen, P Plomgaard, N Ørtenblad

Research output: Contribution to journalJournal articleResearchpeer-review


The effects of short-term high-intensity exercise on single fiber contractile function in humans are unknown. Therefore, the purposes of this study were: (a) to access the acute effects of repeated high-intensity exercise on human single muscle fiber contractile function; and (b) to examine whether contractile function was affected by alterations in the redox balance. Eleven elite cross-country skiers performed four maximal bouts of 1300 m treadmill skiing with 45 min recovery. Contractile function of chemically skinned single fibers from triceps brachii was examined before the first and following the fourth sprint with respect to Ca(2+) sensitivity and maximal Ca(2+) -activated force. To investigate the oxidative effects of exercise on single fiber contractile function, a subset of fibers was incubated with dithiothreitol (DTT) before analysis. Ca(2+) sensitivity was enhanced by exercise in both MHC I (17%, P < 0.05) and MHC II (15%, P < 0.05) fibers. This potentiation was not present after incubation of fibers with DTT. Specific force of both MHC I and MHC II fibers was unaffected by exercise. In conclusion, repeated high-intensity exercise increased Ca(2+) sensitivity in both MHC I and MHC II fibers. This effect was not observed in a reducing environment indicative of an exercise-induced oxidation of the human contractile apparatus.

Original languageEnglish
JournalScandinavian Journal of Medicine & Science in Sports
Issue number5
Pages (from-to)488–497
Publication statusPublished - May 2016


  • Fatigue
  • Muscle fiber
  • Specific force
  • Sprint skiing


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