Mixed
Short-term high-volume resistance training induces muscle hypertrophy primarily through sarcoplasmic expansion (increased sarcoplasmic proteins and glycolytic enzymes) rather than myofibrillar accretion, often accompanied by a decrease in actin and myosin concentrations.
If you are new to resistance training or returning after a break, your initial muscle size gains may come largely from increased fluid and metabolic enzymes (sarcoplasm) rather than thicker muscle fibers. This means you might see visual size increases before significant strength gains. This is a normal, healthy adaptation to high-volume training and does not negate the value of the training.
These data suggest that short-term high-volume resistance training may: a) reduce muscle fiber actin and myosin protein concentrations in spite of increasing fCSA, and b) promote sarcoplasmic expansion coincident with a coordinated up-regulation of sarcoplasmic proteins involved in glycolysis and other metabolic processes related to ATP generation.
Why this rating
Randomized controlled trial with biochemical and proteomic analysis, though small sample size (n=15) and exploratory nature limit generalizability.
Source
Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy
Cody T. Haun et al. · PLoS ONE · 2019
This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →