The Study
Influence of exercise contraction mode and protein supplementation on human skeletal muscle satellite cell content and muscle fiber growth.
This study found that when young men did certain leg exercises and drank protein shakes, their muscles changed in certain ways — but we don’t know if the exercises or shakes actually caused those changes, because we don’t know if they were randomly assigned. So we can only say the changes were linked, not that one thing made the other happen.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
When you lift weights, your muscle fibers get bigger. This study found that slow-twitch fibers grow no matter what you do, but fast-twitch fibers only grow big if you lift in a certain way and drink protein.
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 566 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — if you want bigger fast-twitch muscles (for strength/power), lifting up and taking protein works best.
- 2Slow-twitch muscles grow easily even without special tricks.
- 3Slow-twitch fibers grew 12–22% in all groups.
- 4Fast-twitch fibers grew 25% only when lifting up (concentric) + drinking whey protein.
- 5Satellite cells (muscle repair cells) increased only with lifting up, not down.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Journal of applied physiology
Year
2014
Authors
J. Farup, S. Rahbek, Simon Riis, M. Vendelbo, F. Paoli, K. Vissing
Related Content
Claims (10)
Performing the lowering phase of weightlifting exercises leads to greater increases in muscle size compared to other phases of the same exercises.
In young men, taking whey protein while doing concentric resistance exercises for 12 weeks results in a 25% increase in the size of fast-twitch muscle fibers, but this increase does not occur with eccentric exercises or a placebo.
After 12 weeks of unilateral knee extension training, young men who performed concentric resistance exercises showed higher increases in satellite cells within both slow-twitch and fast-twitch muscle fibers than those who performed eccentric resistance exercises.
Twelve weeks of concentric resistance training increases the number of muscle stem cells in both slow-twitch and fast-twitch muscle fibers of young men by 78–132%, while eccentric resistance training does not increase these cells.
During concentric resistance training, increases in the size of type II muscle fibers are directly linked to overall muscle growth, but during eccentric resistance training, this link does not exist.
After 12 weeks of combining whey protein with concentric resistance training, type II muscle fibers increase in size by approximately 25%. This increase does not occur with eccentric training or placebo.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.