Lifting lighter weights with more reps might make your slow-twitch muscles grow bigger than lifting heavier weights with fewer reps.
Evidence from Studies
Supporting (2)
Community contributions welcome
Type 1 Muscle Fiber Hypertrophy after Blood Flow–restricted Training in Powerlifters
The study used light weights with restricted blood flow and found it made slow-twitch muscle fibers grow more than heavy weights did, which matches the claim.
Heavy or Light
The study found that lifting lighter weights helps grow type I muscle fibers more than heavier weights, which matches the claim, but the results aren't super certain.
Contradicting (2)
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The Effects of Low-Load Vs. High-Load Resistance Training on Muscle Fiber Hypertrophy: A Meta-Analysis
The study looked at the same type of training as the claim but found no proof that lighter weights grow slow-twitch muscles more than heavier weights.
Divergent Strength Gains but Similar Hypertrophy After Low-Load and High-Load Resistance Exercise Training in Trained Individuals: Many Roads Lead to Rome.
The study compared low-weight and high-weight training and found both made muscles grow similarly, without low weights favoring slow-twitch fibers more, which goes against the claim.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.