27/01/2021
One of the great classic bodybuilding myths is the idea of the 6-12 rep hypertrophy zone for maximum muscle growth. This was based on a wrong interpretation of the strength-endurance continuum.
The strength-endurance continuum is a well-established finding, meaning that strength is specific to the rep range you train in. We often reserve the word 'strength' for 1RM strength, but if you want strength-endurance, you may be better off training with higher rep ranges.
Hypertrophy was traditionally placed in the middle of the two, but this makes no logical sense, as hypertrophy is not a performance measure but a morphological adaptation.
Intuitively, it probably made bro sense, because weights at or above 15RM feel 'too light' and heavy weights don't make you get a pump.
However, we now have very strong evidence, supported now by a new meta-analysis by Lopez et al., that muscle growth per set is actually similar across a range of about 5-30 reps, provided you train (close) to failure.
Light weights can be equally effective as heavier weights due to the Size Principle of muscle recruitment: neuromuscular fatigue lowers the recruitment threshold of higher-threshold motor units, causing them to be recruited later in the set even with lighter weights, so in the end you can still subject all motor units to high mechanical tension. Below ~30% of 1RM this doesn't seem to be possible anymore though due to other limiting factors coming into play than muscular tension.
Very heavy weights are effective for muscle growth per rep, but the time under tension is low, so you may need to do more sets to stimulate a given level of muscle growth.
This does not mean your reps per set are irrelevant for muscle growth though. Your rep range still influences strength gains, which may influence muscle growth (see my recent review on this), injury potential, neuromuscular fatigue and possibly which growth pathways are activated. Due to these factors, it's actually best *not* to limit yourself to the 6-12 rep range for maximum muscle growth. You should employ multiple rep ranges in your training.
