Abstract
Combining endurance training with resistance training (RT) may attenuate skeletal muscle hypertrophic adaptation versus RT alone; however, the underlying mechanisms are unclear. We investigated changes in markers of ribosome biogenesis, a process linked with skeletal muscle hypertrophy, following concurrent training versus RT alone. Twenty-three males underwent eight weeks of RT, either performed alone (RT group, n = 8), or combined with either high-intensity interval training (HIT+RT group, n = 8), or moderate-intensity continuous training (MICT+RT group, n = 7). Muscle samples (vastus lateralis) were obtained before training, and immediately before, 1 h and 3 h after the final training session. Training-induced changes in basal expression of the 45S ribosomal RNA (rRNA) precursor (45S pre-rRNA), and 5.8S and 28S mature rRNAs, were greater with concurrent training versus RT. However, during the final training session, RT further increased both mTORC1 (p70S6K1 and rps6 phosphorylation) and 45S pre-rRNA transcription-related signalling (TIF-1A and UBF phosphorylation) versus concurrent training. These data suggest that when performed in a training-accustomed state, RT induces further increases mTORC1 and ribosome biogenesis-related signalling in human skeletal muscle versus concurrent training; however, changes in ribosome biogenesis markers were more favourable following a period of short-term concurrent training versus RT performed alone.
Highlights
Incorporating both resistance and endurance training into a periodised training program, termed concurrent training[1], can attenuate resistance training adaptations such as muscle hypertrophy, compared with resistance training performed alone[2,3,4]
Future studies should consider the potential role of CAD in the regulation of skeletal muscle growth in response to resistance and/or concurrent training. This is the first study to simultaneously investigate markers of ribosome biogenesis and mechanistic target of rapamycin complex 1 (mTORC1) signalling in human skeletal muscle following concurrent training compared with single-mode resistance training
An apparent disconnect was noted between training-induced changes in muscle fibre CSA, of which the small increase in type I fibre CSA induced by resistance training was attenuated when combined with high-intensity interval training (HIT), and changes in total skeletal muscle RNA content
Summary
Incorporating both resistance and endurance training into a periodised training program, termed concurrent training[1], can attenuate resistance training adaptations such as muscle hypertrophy, compared with resistance training performed alone[2,3,4] This effect is potentially mediated by an altered balance between post-exercise skeletal muscle protein synthesis (MPS) and breakdown, subsequently attenuating lean mass accretion. Transient changes in translational efficiency (i.e., rates of protein synthesis per ribosome) after single sessions of concurrent exercise, as indexed by skeletal muscle mTORC1 signalling or rates of MPS, in relatively training-unaccustomed individuals do not appear to explain interference to muscle hypertrophy following longer-term concurrent training. The RNA Pol-II is responsible for the transcription of ribosomal protein-encoding genes, whereas RNA Pol-III mediates the nucleoplasmic transcription of 5S rRNA and tRNAs (transfer RNAs)[26]
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