Did muscles grow by getting bigger or by making new fibers?
Muscle fiber hypertrophy, hyperplasia, and capillary density in college men after resistance training.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Men did weight training for 12 weeks. Scientists checked their arm muscles before and after to see how they changed.
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Systematic Reviews & Meta-Analyses
Max 100Randomized Controlled Trials
Max 90Cohort Studies
Max 72Case-Control Studies
Max 58Cross-Sectional Studies
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Max 30Expert Opinion & Narrative Reviews
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Evidence Score
A snapshot of a population at a single point in time. Can identify correlations and prevalence, but cannot determine the direction of cause and effect.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Men did weight training for 12 weeks. Scientists checked their arm muscles before and after to see how they changed.
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Systematic Reviews & Meta-Analyses
Max 100Randomized Controlled Trials
Max 90Cohort Studies
Max 72Case-Control Studies
Max 58Cross-Sectional Studies
Max 44Case Reports & Case Series
Max 30Expert Opinion & Narrative Reviews
Max 531 / 44
Evidence Score
A snapshot of a population at a single point in time. Can identify correlations and prevalence, but cannot determine the direction of cause and effect.
Publication
Authors
McCall GE, Byrnes WC, Dickinson A, Pattany PM, Fleck SJ
Related Content
Claims (6)
When you lift weights, your muscles get bigger not because you're growing new muscle fibers, but because the ones you already have are getting thicker. Scientists don't think you actually create new muscle fibers from training.
Lifting weights for three months makes the muscle fibers in young men's biceps get bigger — both the endurance-type and power-type fibers.
Lifting weights for three months increases the number of tiny blood vessels in arm muscles of young men, and the growth keeps up with how much the muscle fibers get bigger.
If college guys who've lifted weights before do a specific 12-week workout plan—3 times a week, 8 exercises, 3 sets each—they'll get 25% stronger in their arms, based on how much they can lift in one go on a curl machine.
Lifting weights for three months can make the upper arm muscle about 13% bigger in young college guys.