The untrained arm gets stronger without getting bigger—proving that the improvement comes from better nerve signals, not from muscles growing larger.
Scientific Claim
Cross-education strength gains occur without changes in muscle size (limb circumference or skinfold thickness) in the untrained limb, confirming that early strength improvements are mediated by neural, not hypertrophic, adaptations.
Original Statement
“Untrained limbs presented consistent subcutaneous skinfold thickness and limb circumferences across T0, T1, and T2 (p > 0.05)... Initial gains are typically evident after 4 weeks of resistance training and primarily attributed to neural modifications”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
definitive
Can make definitive causal claims
Assessment Explanation
The RCT design with direct anthropometric measurements allows definitive conclusions about the absence of hypertrophy. The claim correctly attributes strength gain to neural mechanisms.
Evidence from Studies
Supporting (1)
Cross-education: motor unit adaptations mediate the strength increase in non-trained muscles following 8 weeks of unilateral resistance training
When one arm gets stronger from lifting weights, the other arm gets stronger too—even though it didn’t lift anything—because the brain and nerves get better at telling the muscles to work harder, not because the muscles get bigger.