Abstract
Resistance-exercise volume is a determinant of training outcomes. However not all individuals respond in a dose-dependent fashion. In this study, 34 healthy individuals (males n = 16, age 23.6 (4.1) years; females n = 18, 22.0 (1.3) years) performed moderate- (3 sets per exercise, MOD) and low-volume (1 set, LOW) resistance training contralateral fashion for 12 weeks (2-3 sessions × week−1) enabling intra-individual comparisons of effects of training modalities. Muscle cross-sectional area (CSA) and muscle strength was assessed at weeks 0 and 12, along with biopsy sampling (m. Vastus lateralis). Muscle biopsies were also sampled before and one hour after the fifth session (Week 2). MOD resulted in larger increases in muscle CSA (5.2 (3.8)% versus 3.7 (3.7)%, P < 0.001) and strength (3.4-7.7% difference, all P < 0.05). In muscle, this coincided with greater reductions in type IIX fibres from week 0 to week 12 (MOD, −4.6 vs. LOW - 3.2%-point), greater post-exercise (Week 2) phosphorylation of mTOR (12%), S6-kinase 1 (19%) and ribosomal protein S6 (28%, Week 2), greater rested-state total RNA (8.8%, Week 2) and greater exercise-induced elevation of c-Myc mRNA expression (25%, Week 2; all P < 0.05). Fifteen participants displayed robust benefits of MOD on muscle hypertrophy. This was associated with greater accumulation of total RNA at Week 2 in MOD vs. LOW as every 1% difference increased the odds of MOD benefit by 5.4% (P = 0.010). In conclusion, MOD led to on average greater adaptations to resistance training and dose-dependent hypertrophy was associated with volume-dependent regulation of total RNA at week 2. This suggests that ribosomal biogenesis regulates the dose-response relationship between training volume and muscle hypertrophy.
Key points
For individuals showing suboptimal adaptations to resistance training, manipulation of training volume is a potential measure to facilitate responses. This remains unexplored in previous research.
Here, 34 untrained individuals performed contralateral resistance training with moderate and low volume for 12 weeks. Overall, moderate volume led to larger increases in muscle cross-sectional area, strength and type II fibre-type transitions.
These changes coincided with greater activation of signaling pathways controlling muscle growth and greater induction of ribosome synthesis.
Fifteen individuals displayed clear benefit of moderate-volume training on muscle hypertrophy. This coincided with greater total RNA accumulation in the early-phase of the training period, suggesting that ribosomal biogenesis regulates the dose-response relationship between training volume and muscle hypertrophy.
These results demonstrate that there is a dose-dependent relationship between training volume and muscle hypertrophy. On the individual level, benefits of higher training volume was associated with increased ribosomal biogenesis.
