Whether you use light or heavy weights, your muscles can grow about the same amount if you train hard enough—both methods work for building muscle size.
Scientific Claim
Both low-load and high-load resistance training are associated with similar increases in muscle thickness (7 ± 17% at mid-thigh, 8 ± 8% at distal site) in resistance-trained adults after 9 weeks of training.
Original Statement
“Regardless of training regimen, muscle thickness increased pre- to postintervention by 7 ± 17% at the mid-thigh site and 8 ± 8% at the distal site.”
Evidence Quality Assessment
Claim Status
overstated
Study Design Support
Design cannot support claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The abstract implies equivalence but does not confirm RCT design; thus, 'similar increases' should be framed as association, not equivalence or causation.
Evidence from Studies
Supporting (1)
Divergent Strength Gains but Similar Hypertrophy After Low-Load and High-Load Resistance Exercise Training in Trained Individuals: Many Roads Lead to Rome.
This study found that lifting light weights for many reps and lifting heavy weights for few reps both made people’s thighs about the same size after 9 weeks — so neither method is clearly better for building muscle size.