The Study
Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy
This study watched a group of trained young men over 6 weeks of intense weight training and took muscle samples to see what changed. It shows what happened, but not why it happened or if the training directly caused the changes.
Analysis score
Maximum 72 for a cohort study.
Where the score came from
When strong young guys lift weights a lot for 6 weeks, their muscle fibers get bigger, but not because they add more muscle-building proteins. Instead, the inside fluid and energy-making parts of the cell grow more.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 539 / 100
Quality score
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Key takeaways
Summary
Based on the study abstract and findings.
- 1The muscle gets bigger but may not get stronger right away because the actual 'engine' parts don’t increase—instead, the fuel and fluid systems expand.
- 2Muscle fibers grew 23%.
- 3Muscle proteins (actin and myosin) dropped by ~30%.
- 4Sarcoplasmic proteins went up 66% and stayed high 8 days later.
- 5Mitochondria activity dropped 24%.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
PLoS ONE
Year
2019
Authors
Cody T Haun, C. Vann, Shelby C. Osburn, Petey W. Mumford, Paul A. Roberson, M. Romero, Carlton D. Fox, Christopher A. Johnson, Hailey A. Parry, A. Kavazis, Jordan R. Moon, Veera L.D. Badsia, B. Mwashote, V. Ibeanusi, Kaelin C. Young, M. Roberts
Related Content
Claims (8)
Even the muscles that are built for endurance can get bigger—like, over 10% bigger—if you do the right kind of strength training for a few months. This goes against what people used to think.
When young guys who already work out do a lot of high-volume weight training for 6 weeks, their muscles grow mostly because of fluid and non-contracting parts inside the muscle cells, not because they’re building more of the actual muscle-building proteins — and this change sticks around for over a week after they stop training.
When young guys who already work out do a lot of high-rep weight training for a short time, their muscles get bigger but their energy-producing parts actually become less dense, meaning bigger muscles don’t always mean more energy factories inside them.
Lifting heavy weights for six weeks changes specific proteins in the muscles of fit young men. This suggests their muscles are switching to a way of making energy that doesn't require oxygen.
After young guys stop intense weight training, their muscle proteins stay low for over a week, suggesting it's not just temporary swelling or soreness.
Even though muscle fibers get 23% bigger with high-rep training, the amount of actin protein inside doesn’t go up, and the usual tight link between fiber size and actin breaks down.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.