Meta-analysis — 2017 — Repetitions & load · Hypertrophy · Strength
Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-analysis
What did the researchers investigate?
Strength and muscle growth with low loads (60% of 1RM or less) versus high loads (more than 60%), all sets to failure, across 21 studies.
What did they find?
1RM strength gains were greater with high loads, with no difference in isometric strength. Muscle growth was similar between conditions.
What does this mean for training?
Maximal strength benefits from heavier loads, while muscle growth can be achieved across a spectrum of loads.
How does FitX AI use this evidence?
FitX AI uses a moderate default range (8-15 reps) and estimates your 1RM so loads stay meaningful as you get stronger.
Where FitX AI's own choices go beyond this paper
8-15 working range. 8-15 is a practical default range, not a research-derived limit. 6-10 for barbell squats and hinges, and RPE 9 as their ceiling, are FitX AI choices to limit the fatigue of the most demanding lifts: no paper sets these numbers. A range the user has set is never changed.
Session check. Flagging a heavy squat or hinge with a top of range above 12 and 3+ sets, more than 6 hard sets of those lifts in a session, and three same-movement exercises for one muscle are FitX AI heuristics. Exercise order (early exercises get more reps and progress more for strength) is from reviews logged as candidates, not yet in the library. Fatigue varies by person, so these are pointers, never limits.
Limitations
All included studies took sets to failure, so the results may not transfer directly to training that stops short of failure.