Randomised trial — 2015 — Repetitions & load · Hypertrophy · Strength
Effects of Low- vs. High-Load Resistance Training on Muscle Strength and Hypertrophy in Well-Trained Men
What did the researchers investigate?
Low-load (25-35 reps) versus high-load (8-12 reps) training to failure, 3 times a week for 8 weeks, in 18 well-trained young men.
What did they find?
Both groups increased muscle thickness with no significant difference between them. Back-squat strength improved more with heavier loads, with a trend for bench press; muscular endurance improved more with light loads.
What does this mean for training?
Muscle can grow across a wide range of reps when sets are hard, but heavier loads are better for maximal strength.
How does FitX AI use this evidence?
FitX AI's default 8-15 range sits in the moderate zone: heavy enough to support strength, with reps high enough for practical, safe sets.
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.
Limitations
18 participants over 8 weeks, all sets to failure, young men only.