Mixed
Resistance training using light loads (30% 1RM) performed to momentary failure produces equivalent muscle hypertrophy to heavy loads (80% 1RM) in young men.
You do not need to lift heavy weights to build muscle. If you use a lighter weight (around 30% of your max), you must perform enough reps to reach momentary failure (where you cannot complete another rep with good form). Doing this 3 times a week for 10 weeks will build muscle just as effectively as lifting heavy weights. However, note that lifting heavy weights is still better for maximizing raw strength numbers.
In accordance with our previous acute measurements of muscle protein synthetic rates a lower load lifted to failure resulted in similar hypertrophy as a heavy load lifted to failure.
Why this rating
Randomized controlled trial with objective MRI measures and adequate sample size for the design, though short duration (10 weeks).
Source
Resistance exercise load does not determine training-mediated hypertrophic gains in young men
Cameron J. Mitchell et al. · Journal of Applied Physiology · 2012
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