Training one arm with heavy weights improves its overall strength and endurance, but does not improve how efficiently that arm can perform repeated movements relative to its body weight or starting...
Mechanism
Synthesis from 1 study
Training one arm hard makes the brain send stronger signals to both arms, so the other arm can do more reps. But since the untrained arm didn't get stronger relative to how strong it was before, its endurance improvement doesn't count as better efficiency — just more power.
Most probable mechanism
When one arm is trained with heavy weights, the brain sends stronger signals to both arms, making the untrained arm stronger and able to do more reps. But because the untrained arm didn't get bigger or change how efficiently it uses its existing strength, its endurance relative to its starting ability doesn't improve — it just gets a little stronger overall.
High-load resistance training induces neuroplastic changes in the primary motor cortex of the trained hemisphere, increasing its output signal strength.
Enhanced neural activity in the trained motor cortex increases transcallosal signaling to the contralateral motor cortex, boosting excitability in the untrained limb's motor pathways.
Corticospinal pathways to the untrained limb become more efficient, increasing motor unit recruitment and firing rates during muscle contractions.
The untrained limb produces greater absolute force and can sustain more repetitions due to improved neural drive, but muscle size and metabolic efficiency remain unchanged.
Because relative endurance is calculated relative to baseline strength or body weight, and the untrained limb's baseline capacity did not shift proportionally to its new strength, its endurance relative to its original capacity remains unchanged.
Evidence from Studies
Supporting (1)
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Unilateral High-Load Resistance Training Increases Absolute but Not Relative Muscular Endurance in the Contralateral Untrained Limb
Contradicting (0)
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