Lifting lighter weights many times in a row might help grow certain slow-twitch muscles better because they stay working longer.
Evidence from Studies
Supporting (1)
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The study looks at how longer muscle tension during exercise helps muscles grow, which matches the idea that doing more reps with slower movements benefits certain muscle fibers.
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 lifting light weights many times versus heavy weights fewer times and found no difference in how much either type of muscle fiber grew, so it doesn't support the idea that many reps are better for certain muscles.
High force development augments skeletal muscle signalling in resistance exercise modes equalized for time under tension
The study shows that lifting heavy weights with high force gives better muscle-building signals than doing many lighter reps, and it works more on fast-twitch muscles, not the slow-twitch ones mentioned in 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.