Meta-analysis — 2023 — RPE & autoregulation · Hypertrophy
Influence of Resistance Training Proximity-to-Failure on Skeletal Muscle Hypertrophy: A Systematic Review with Meta-analysis
What did the researchers investigate?
Whether taking sets to failure produces more muscle growth than stopping short, across 15 studies.
What did they find?
Training to any definition of set failure had a trivial advantage over non-failure. When restricted to momentary muscular failure, there was no advantage, and higher velocity-loss thresholds (closer to failure) did not always produce more growth. The authors suggest a possibly non-linear relationship.
What does this mean for training?
You don't need to grind every set to failure. Training reasonably close to failure appears to be enough for muscle growth.
How does FitX AI use this evidence?
FitX AI only asks for a true all-out effort (RPE 10) on the last set of the hardest week. Most sets finish with 1-3 reps left.
Where FitX AI's own choices go beyond this paper
RPE mesocycle. The 7, 8, 9, 10 ladder and the 5-week length are FitX AI design choices. The papers support training near failure and RPE/RIR as effort scales, not this exact schedule.
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
Studies defined failure in different ways; the authors ran subgroup analyses to account for this.