Some people’s muscles grow a lot with training, others don’t—but if one person’s arms grow, their legs usually grow similarly, meaning your body’s natural response is more important than which muscle you train.
Scientific Claim
Interindividual variability in muscle hypertrophy from resistance training is greater between individuals than within individuals across upper and lower limbs, suggesting that biological factors unique to each person strongly influence muscle growth responses.
Original Statement
“Despite considerable interindividual variability in hypertrophic responses, we observed that muscle hypertrophy following RET was relatively well conserved within versus between subjects...”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The claim is descriptive and based on observed within-subject consistency and between-subject variation. No causal language is used, and the design supports this type of observation.
Evidence from Studies
Supporting (1)
Resistance training load does not determine resistance training-induced hypertrophy across upper and lower limbs in healthy young males.
Even when people trained their arms and legs with different weights, each person’s muscles grew about the same amount in both areas—suggesting that your body’s natural biology, not the workout details, is what mostly determines how much you grow.