People who grow their arms big don’t necessarily grow their legs big, and vice versa — muscle growth varies by person, not just by how heavy they lift.
Scientific Claim
Individual hypertrophic responses to resistance training are highly variable across muscle groups and are not consistently correlated between upper and lower body musculature.
Original Statement
“We have another study comparing heavier to lighter loads for muscle hypertrophy, and its design provides insight into some other questions. For example, it's not uncommon for some to suggest that they can grow certain muscles easier than others. This new study provides insight into the question, 'Do people who grow their arms well also tend to grow their legs well?' 20 previously untrained men were recruited to train three times per week for 10 weeks. Subjects had one arm and leg randomly assigned to train with heavier loads, while the contralateral arm and leg trained with lighter loads.”
Context Details
Domain
exercise
Population
human
Subject
Individual hypertrophic responses
Action
are not consistently correlated
Target
between upper and lower body musculature
Intervention Details
Evidence from Studies
Supporting (4)
Can muscle typology explain the inter‐individual variability in resistance training adaptations?
Even when everyone did the same workouts, some people’s muscles grew a lot and others’ didn’t—and this happened differently in arms vs. legs, meaning people respond to training in their own unique way.
Some older women got much stronger in their legs after training, but not in their arms—even if they were already strong or weak to begin with—showing that muscles in different parts of the body don’t always respond the same way.
Resistance training load does not determine resistance training-induced hypertrophy across upper and lower limbs in healthy young males.
People respond differently to weight training, and how much their muscles grow can vary a lot from person to person—even between their arms and legs—because of their biology, not just how heavy they lift.
Resistance training load does not determine resistance training-induced hypertrophy across upper and lower limbs in healthy young males.
The study found that people’s muscles grow differently from person to person, and while one person’s arms and legs might grow similarly, that doesn’t mean everyone’s will—so responses aren’t the same across body parts for everyone.
Contradicting (1)
This study only looked at leg muscles and found that bigger legs usually mean stronger legs, but it didn’t check arms or compare arms to legs, so it doesn’t tell us if people’s arms and legs grow differently.