Resistance-training (RT) is widely recommended for improving health of several populations. However, several aspects involving RT and the affected mechanisms are not well understood, preventing a RT prescription that allows optimizing/maximizing gains in muscle mass (i.e., muscle hypertrophy). Thus, despite it is suggested that the adequate manipulation of RT variables such as load (intensity), number of sets and repetitions (volume), contraction (e.g., eccentric or concentric), rest interval, may optimize/maximize muscle hypertrophy, it remains unknown whether muscle hypertrophy variability between subjects is due the manner that these variables are manipulated or due human biologic variability, which would exclude the influence of RT manipulation. Hence, we propose 10 week of unilateral RT performed by resistance-trained men to analyze the individual biological responsiveness of RT to muscle failure in two conditions: 1) RT performed consistently (RT-CON) - leg 1 (n = 20); 2) RT with variation of load (kg), series, repetitions, type of contraction and rest interval (RT-VAR) - leg 2 (n = 20). There will be analyzed muscle biopsies CSAf and amount of satellite cells (histochemical analysis) and expression of genes (by real time PCR), related to hypertrophy. Our objectives are: 1) to compare the effect of RT performed to muscle failure with variation (RT-VAR) of the RT variables, with a RT protocol also performed until failure, but without variation (RT-CON), in CSAf of fibers type I and II; 2) to compare the intra-subject response of one leg executing the RT-VAR with the other leg performing the RT-CON; and 3) to verify whether individual biological variability can be explained by changes in satellite cell contents and genetic expression of MGF and MRFs (myogen factor 5 [Myf-5] and myogenic factor [MyoD], Myf-6, myogenin and MRF4 ). We hypothesize that: 1) there will be no difference in the hypertrophy of type I and II fibers between RT-VAR and RT-CON; 2) the magnitude of muscular hypertrophy will be more related to biological individuality than the form in which RT is performed; and 3) the content of satellite cells, number of myonuclei and the expression of MGF will be increased in individuals with higher muscle hypertrophy, regardless of the training protocol.
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