After four weeks of resistance training, neuromuscular adaptations measured via electromyography, mechanomyography, and voluntary activation during submaximal contractions are similar between high-load (80% 1RM) and low-load (30% 1RM) protocols, despite greater strength gains in the high-load group.

When muscles grow larger from training, they become stiffer and more efficient at producing force, so the nervous system doesn't need to activate as many motor units to lift the same light weight. But when lifting very heavy weights, the nervous system recruits more motor units and fires them faster, which builds greater maximum strength. This is why both groups get stronger at light lifts the same way, but only the heavy-lifting group gets much stronger at maximum efforts.