Mixed
Resistance training with volume equated across intensities of 40% to 80% 1RM produces equivalent muscle hypertrophy, whereas 20% 1RM is suboptimal for maximizing muscle size.
To maximize muscle growth, you do not need to lift extremely heavy weights. Training with loads between 40% and 80% of your one-rep max is just as effective for building muscle as lifting heavier weights, provided you perform enough total work (volume) and train close to failure. However, lifting very light weights (20% 1RM) is not enough to maximize muscle size, even if you do many reps. Aim for moderate weights that allow you to complete the required reps with good form near failure.
In conclusion, when low to high intensities of RT are performed with volume-matched, all intensities were effective for increasing muscle strength and size; however, 20% 1RM was suboptimal in this regard, and only the heavier RT intensity (80% 1RM) was shown superior for increasing strength and CSA compared to low intensities.
Why this rating
Randomized controlled trial with within-subject design, equated volume, and clear statistical significance for the main finding.
Source
Effects of different intensities of resistance training with equated volume load on muscle strength and hypertrophy
Thiago Lasevicius et al. · European Journal of Sport Science · 2018
This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →