Do I need to lift heavy to build muscle?
No: anything from roughly 5 to 30 reps builds similar muscle, provided you take the set close to failure.
Strength is the exception: getting stronger at a heavy single is a skill that requires practising heavy singles. If your goal is size, load is a variable you can pick for joint comfort and equipment availability.
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- Schoenfeld, B.J. et al. (2017). Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-analysis. J Strength Cond Res 31(12). Hypertrophy similar; strength favoured heavy loads.
- Lopez, P. et al. (2021). Resistance Training Load Effects on Muscle Hypertrophy and Strength Gain: Systematic Review and Network Meta-analysis. Med Sci Sports Exerc 53(6). Confirmed the load-independence of hypertrophy.