The stronger the untrained arm gets, the more consistently its motor nerves fire during effort—this tight link shows that better nerve signaling, not muscle growth, is why the arm gets stronger.
Scientific Claim
The increase in maximal voluntary force in the untrained limb is strongly linearly associated with the increase in net discharge rate (R² = 0.78), suggesting that enhanced spinal motoneuron output is a primary neural mechanism underlying cross-education.
Original Statement
“We also found a strong linear association between the change in the net discharge rate and the maximal voluntary force in the untrained side between T0 and T2 (R² = 0.78, p = 0.001)”
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 repeated measures and direct motor unit tracking allows for causal interpretation of the association. The verb 'suggesting' appropriately reflects the mechanistic inference without overclaiming spinal causality.
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 people trained one arm, their other arm got stronger too—and this happened because their brain and spinal cord sent stronger signals to the muscles, even without training them.