Hypertrophy Science - What's The Best Load and Repetition Range?

Mechanical tension seems to be the primary drive for the hypertrophic response (1,2). Mechanical forces are converted into chemical signals in a process called mechanotransduction. This causes molecular and cellular responses in myofibers and satellite cells (3), and mechanical stress alone can directly stimulate mTOR (initiation of protein synthesis) (4,5).

A muscle does not know what it contracts against; it just contracts or relaxes (6).
Training to failure, recruiting as many motor units as possible seems optimal (7). This Intensity of effort is perhaps the single most influential controllable variable for enhancing muscular strength, however untrained subjects have a diminished ability to recruit motor units (8).

The recruitment of motor units and muscle fibers stimulates muscular growth irrespective of what has caused that recruitment. This can be achieved with higher or lower loads and respectively lower or higher repetitions (8). Lighter loads lifted to the point of failure result in a similar amount of muscle fiber activation compared with heavier loads, and both fiber types are stimulated to a roughly equivalent extent (10,11).

There appears to be no difference in the hypertrophic response so long as fatigue is induced. In fifting heavy or lighter loads there’s roughly equivalent hypertrophy and strength gains (9,-17).

- One study compared 80%RM vs 30%RM sets to failure with no significant differences between groups for “recreationally active subjects” (10);

- Another compared 3 sets with 75%RM to 4 sets with 30%RM to “volitional fatigue”, again with similar increases in muscle cross-sectional area for untrained subjects (11);

- 3–5 vs. 20–28 of repetitions for each exercise, “until fatigue” with approximately equal volume, also showed no differences for “physically active” subjects (12);

- Lower loads, when combined with vascular occlusion, promote equivalent hypertrophy than heavier loads with the same number of sets and similar volume: 50%-30%RM vs. 80%-50%RM “until failure” for “relatively well-trained subjects” (14) and 50%RM vs. 80%RM “to exhaustion” in untrained subjects (15);

- In another study by Schoenfeld et al. (16) comparing powerlifting style training (low reps, higher loads) versus hypertrophy style (higher reps and moderate loads), this time with equalized volume and also to momentary muscular failure, there was no difference in the hypertrophy magnitude after 8 weeks for “well-trained men”. 

(Note: untrained subject will respond well to any stimulus, just like obese subjects will respond well to any diet, however note that the same trend is found in trained subjects, otherwise it would be irrelevant.)

However lifting moderate loads for moderate repetitions is less taxing to the nervous system, joints, and is time efficient compared to higher loads and low repetition ranges, subjects from the hypertrophy group could do more volume if necessary (16).

Training to failure could sometimes lead to overuse injuries (18,19) and for some people could even reduce the levels of IGF-1 hormones responsible for muscle growth after at least 11 weeks (20).

So in short, if momentary failure is achieved it doesn’t matter how many reps are performed and under what load.

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