Why Muscles Grow Bigger Without More Muscle Power
Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
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.
Surprising Findings
Muscle fibers grew 23%, but contractile protein concentrations decreased.
Conventional wisdom says muscle growth = more actin and myosin. This flips that idea—growth happened *despite* losing key structural proteins.
Practical Takeaways
If you want strength, focus on heavy lifting with lower reps. If you want size, high-volume training works—but don’t expect strength or endurance to improve automatically.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
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.
Surprising Findings
Muscle fibers grew 23%, but contractile protein concentrations decreased.
Conventional wisdom says muscle growth = more actin and myosin. This flips that idea—growth happened *despite* losing key structural proteins.
Practical Takeaways
If you want strength, focus on heavy lifting with lower reps. If you want size, high-volume training works—but don’t expect strength or endurance to improve automatically.
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
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Claims (6)
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.