Physiological Differences Between Low Versus High Skeletal Muscle Hypertrophic Responders to Resistance Exercise Training: Current Perspectives and Future Research Directions
Open Access
- 4 July 2018
- journal article
- review article
- Published by Frontiers Media SA in Frontiers in Physiology
- Vol. 9, 834
- https://doi.org/10.3389/fphys.2018.00834
Abstract
Numerous reports suggest there are low and high skeletal muscle hypertrophic responders following weeks to months of structured resistance exercise training (referred to as low and high responders herein). Specifically, divergent alterations in muscle fiber cross sectional area (fCSA), vastus lateralis thickness, and whole body lean tissue mass have been shown to occur in high versus low responders. Differential responses in ribosome biogenesis and subsequent protein synthetic rates during training seemingly explain some of this individual variation in humans, and mechanistic in vitro and rodent studies provide further evidence that ribosome biogenesis is critical for muscle hypertrophy. High responders may experience a greater increase in satellite cell proliferation during training versus low responders. This phenomenon could serve to maintain an adequate myonuclear domain size or assist in extracellular remodeling to support myofiber growth. High responders may also express a muscle microRNA profile during training that enhances insulinlike growth factor-1 (IGF-1) mRNA expression, although more studies are needed to better validate this mechanism. Higher intramuscular androgen receptor protein content has been reported in high versus low responders following training, and this mechanism may enhance the hypertrophic effects of testosterone during training. While high responders likely possess "good genetics," such evidence has been confined to single gene candidates which typically share marginal variance with hypertrophic outcomes following training (e.g., different myostatin and IGF-1 alleles). Limited evidence also suggests pre-training muscle fiber type composition and self-reported dietary habits (e.g., calorie and protein intake) do not differ between high versus low responders. Only a handful of studies have examined muscle biomarkers that are differentially expressed between low versus high responders. Thus, other molecular and physiological variables which could potentially affect the skeletal muscle hypertrophic response to resistance exercise training are also discussed including rDNA copy number, extracellular matrix and connective tissue properties, the inflammatory response to training, and mitochondrial as well as vascular characteristics.Keywords
This publication has 150 references indexed in Scilit:
- Resistance exercise load does not determine training-mediated hypertrophic gains in young menJournal of Applied Physiology, 2012
- Mechanotransduction and the regulation of mTORC1 signaling in skeletal muscleThe International Journal of Biochemistry & Cell Biology, 2011
- Influence of acetaminophen and ibuprofen on skeletal muscle adaptations to resistance exercise in older adultsAmerican Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2011
- Translational signaling responses preceding resistance training-mediated myofiber hypertrophy in young and old humansJournal of Applied Physiology, 2009
- Myostatin inhibits IGF-I-induced myotube hypertrophy through AktAmerican Journal of Physiology-Cell Physiology, 2009
- Overload‐induced skeletal muscle extracellular matrix remodelling and myofibre growth in mice lacking IL‐6Acta Physiologica, 2009
- Does habitual dietary intake influence myofiber hypertrophy in response to resistance training? A cluster analysisApplied Physiology, Nutrition, and Metabolism, 2009
- Muscle expression of genes associated with inflammation, growth, and remodeling is strongly correlated in older adults with resistance training outcomesPhysiological Genomics, 2009
- Rapamycin administration in humans blocks the contraction‐induced increase in skeletal muscle protein synthesisThe Journal of Physiology, 2009
- Nutritional aspects of women strength athletesBritish Journal of Sports Medicine, 2006