| Summary: | The purpose of the study was to compare the physiological responses of skeletal muscle to a resistance training (RT) program using repetition maximum (RM) or relative intensity (RI<sub>SR</sub>). Fifteen well-trained males underwent RT 3 d·wk<sup>−1</sup> for 10 weeks in either an RM group (<i>n</i> = 8) or RI<sub>SR</sub> group (<i>n</i> = 7). The RM group achieved a relative maximum each day, while the RI<sub>SR</sub> group trained based on percentages. The RM group exercised until muscular failure on each exercise, while the RI<sub>SR</sub> group did not reach muscular failure throughout the intervention. Percutaneous needle biopsies of the vastus lateralis were obtained pre-post the training intervention, along with ultrasonography measures. Dependent variables were: Fiber type-specific cross-sectional area (CSA); anatomical CSA (ACSA); muscle thickness (MT); mammalian target of rapamycin (mTOR); adenosine monophosphate protein kinase (AMPK); and myosin heavy chains (MHC) specific for type I (MHC1), type IIA (MHC2A), and type IIX (MHC2X). Mixed-design analysis of variance and effect size using Hedge’s <i>g</i> were used to assess within- and between-group alterations. RI<sub>SR</sub> statistically increased type I CSA (<i>p</i> = 0.018, <i>g</i> = 0.56), type II CSA (<i>p</i> = 0.012, <i>g</i> = 0.81), ACSA (<i>p</i> = 0.002, <i>g</i> = 0.53), and MT (<i>p</i> < 0.001, <i>g</i> = 1.47). RI<sub>SR</sub> also yielded a significant mTOR reduction (<i>p</i> = 0.031, <i>g</i> = −1.40). Conversely, RM statistically increased only MT (<i>p</i> = 0.003, <i>g</i> = 0.80). Between-group effect sizes supported RI<sub>SR</sub> for type I CSA (<i>g</i> = 0.48), type II CSA (<i>g</i> = 0.50), ACSA (<i>g</i> = 1.03), MT (<i>g</i> = 0.72), MHC2X (<i>g</i> = 0.31), MHC2A (<i>g</i> = 0.87), and MHC1 (<i>g</i> = 0.59); with all other effects being of trivial magnitude (<i>g</i> < 0.20). Our results demonstrated greater adaptations in fiber size, whole-muscle size, and several key contractile proteins when using RI<sub>SR</sub> compared to RM loading paradigms.
|
|---|
