Abstract
We sought to identify biomarkers which delineated individual hypertrophic responses to resistance training. Untrained, college-aged males engaged in full-body resistance training (3 d/wk) for 12 weeks. Body composition via dual x-ray absorptiometry (DXA), vastus lateralis (VL) thickness via ultrasound, blood, VL muscle biopsies, and three-repetition maximum (3-RM) squat strength were obtained prior to (PRE) and following (POST) 12 weeks of training. K-means cluster analysis based on VL thickness changes identified LOW [n = 17; change (mean±SD) = +0.11±0.14 cm], modest (MOD; n = 29, +0.40±0.06 cm), and high (HI; n = 21, +0.69±0.14 cm) responders. Biomarkers related to histology, ribosome biogenesis, proteolysis, inflammation, and androgen signaling were analyzed between clusters. There were main effects of time (POST>PRE, p<0.05) but no cluster×time interactions for increases in DXA lean body mass, type I and II muscle fiber cross sectional area and myonuclear number, satellite cell number, and macronutrients consumed. Interestingly, PRE VL thickness was ~12% greater in LOW versus HI (p = 0.021), despite POST values being ~12% greater in HI versus LOW (p = 0.006). However there was only a weak correlation between PRE VL thickness scores and change in VL thickness (r2 = 0.114, p = 0.005). Forced post hoc analysis indicated that muscle total RNA levels (i.e., ribosome density) did not significantly increase in the LOW cluster (351±70 ng/mg to 380±62, p = 0.253), but increased in the MOD (369±115 to 429±92, p = 0.009) and HI clusters (356±77 to 470±134, p<0.001; POST HI>POST LOW, p = 0.013). Nonetheless, there was only a weak association between change in muscle total RNA and VL thickness (r2 = 0.079, p = 0.026). IL-1β mRNA levels decreased in the MOD and HI clusters following training (p<0.05), although associations between this marker and VL thickness changes were not significant (r2 = 0.0002, p = 0.919). In conclusion, individuals with lower pre-training VL thickness values and greater increases muscle total RNA levels following 12 weeks of resistance training experienced greater VL muscle growth, although these biomarkers individually explained only ~8–11% of the variance in hypertrophy.
Highlights
Resistance training is a potent stimulus for skeletal muscle fiber hypertrophy
Recent data [3, 4] and commentaries [5, 6] have suggested ribosome biogenesis is critical for muscle hypertrophy given that ribosomes catalyze muscle protein synthesis (MPS)
Ribosome biogenesis involves the coordinated action of transcription factors and transcriptional co-activators [e.g., v-Myc Avian Myelocytomatosis Viral Oncogene Homolog (c-Myc), Upstream Binding Factor (UBF), and others] recruiting RNA polymerase I (Pol I) to repetitive rDNA promoter regions to facilitate 47S pre-rRNA transcription [6, 7]
Summary
Resistance training is a potent stimulus for skeletal muscle fiber hypertrophy. Recent data [3, 4] and commentaries [5, 6] have suggested ribosome biogenesis is critical for muscle hypertrophy given that ribosomes catalyze MPS. Ribosome biogenesis involves the coordinated action of transcription factors and transcriptional co-activators [e.g., v-Myc Avian Myelocytomatosis Viral Oncogene Homolog (c-Myc), Upstream Binding Factor (UBF), and others] recruiting RNA polymerase I (Pol I) to repetitive rDNA promoter regions to facilitate 47S pre-rRNA transcription [6, 7]. Aside from the abovementioned studies, there is limited evidence examining if various markers of ribosome biogenesis coincide with skeletal muscle hypertrophy following resistance training in humans
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