Even if you lift light weights, if you go until you can’t do another rep, your muscles end up using almost all the same fibers as if you lifted heavy — which might be why both ways make muscles grow similarly.
Scientific Claim
The physiological mechanism of motor unit recruitment under load may explain why low-load and high-load training produce similar muscle fiber hypertrophy when performed to failure, as both may ultimately recruit the full spectrum of motor units.
Original Statement
“According to Henneman's size principle... as these motor units fatigue, higher threshold motor units associated with type II muscle fibers will be recruited, ultimately resulting in the recruitment of the entire motor unit pool... similar recruitment of motor units with low-load and high-load training may, over time, also result in comparable hypertrophy of muscle fibers.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design cannot support claim
Appropriate Language Strength
probability
Can suggest probability/likelihood
Assessment Explanation
The claim is framed as a hypothesis ('may explain', 'may result'), consistent with the authors’ language. The study design cannot test mechanisms directly, so probability verbs are appropriate.
Evidence from Studies
Supporting (1)
The Effects of Low-Load Vs. High-Load Resistance Training on Muscle Fiber Hypertrophy: A Meta-Analysis
Even if you lift light weights or heavy ones, if you push until you can’t do another rep, your muscles grow about the same—probably because your body uses all its muscle fibers in both cases.