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Fatigue Pattern in Subtypes of Human Skeletal Muscle FibersThis study was supported by grants from the Swedish Medical Research Council (Project No. 4251), the Research Council of the Swedish Sports Federation and the National Defence Research Institute.
14 March 2008 (online)
Physically active young men (n = 23) were studied in terms of susceptibility to muscle fatigue. The monitored decrease in peak torque during repeated isokinetic knee extensions was used as an index for fatigue. Tissue specimens from m. vastus lateralis were obtained and analyzed for their relative distribution of muscle fiber types based on a histochemical staining procedure separating fibers into three categories due to different ATPase systems: ST (slow twitch), FTa (fast twitch), and FTb (fast twitch). In accordance with previous studies, muscle fatigue was found to be related to the relative distribution of FT fibers. However, when considering the individual percentage of FTb fibers, the same correlation coefficients were demonstrated. In confirming with the different metabolic and vascular profiles of the two FT fiber subtypes, it is suggested that FTb fibers are most susceptible to fatigue while the FTa fibers represent an intermediate fiber type in this regard.
fatigue - FT subtypes - muscle fibers - human skeletal muscle