Why some people grow muscles faster than others
Can muscle typology explain the inter‐individual variability in resistance training adaptations?
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Surprising Findings
Muscle typology (slow vs. fast fibers) did NOT predict who gained more muscle or strength.
For decades, fitness culture assumed fast-twitch fibers grow more easily. This study found no link between fiber type and response—even though people’s gains varied wildly (+3% to +14% muscle growth).
Practical Takeaways
If you’re not seeing results, increase your weekly training volume—especially if you suspect you have more slow-twitch fibers (e.g., endurance athletes, naturally lean build).
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Surprising Findings
Muscle typology (slow vs. fast fibers) did NOT predict who gained more muscle or strength.
For decades, fitness culture assumed fast-twitch fibers grow more easily. This study found no link between fiber type and response—even though people’s gains varied wildly (+3% to +14% muscle growth).
Practical Takeaways
If you’re not seeing results, increase your weekly training volume—especially if you suspect you have more slow-twitch fibers (e.g., endurance athletes, naturally lean build).
Publication
Journal
The Journal of Physiology
Year
2023
Authors
Kim Van Vossel, Julie Hardeel, Freek Van de Casteele, Thibaux Van der Stede, Anneleen Weyns, Jan Boone, Silvia Salinas Blemker, Eline Lievens, Wim Derave
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Claims (7)
Even though muscles get bigger after 10 weeks of weightlifting, the individual muscle fibers don’t necessarily get thicker — the growth might come from how the fibers are arranged, not from each one swelling up.
When people lift weights until they can’t do another rep, both slow-twitch and fast-twitch muscle fibers grow at about the same rate — so fast-twitch fibers aren’t naturally better at getting bigger.
Whether someone has more slow-twitch or fast-twitch muscle fibers doesn't predict how much bigger or stronger their muscles will get after 10 weeks of lifting weights to exhaustion, even though people's results vary a lot.
People with more slow-twitch muscles have to do more reps and lift more total weight to get the same muscle growth as people with more fast-twitch muscles, even when both train until exhaustion.
Lifting weights three times a week instead of two makes your muscles grow bigger, no matter what type of muscle fibers you have — but it doesn’t make you stronger in one-rep max lifts.