descriptive
You need to lift weights at least 30% as heavy as your max to get the best muscle growth—lighter than that gives you only half the results, but flexing really hard with no weight can still build a little muscle.
Evidence from Studies
Supporting (1)
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Contradicting (0)
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No contradicting evidence found
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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.