In trained men undergoing high-load lower-body resistance training, the electromyographic (EMG) amplitude of the vastus lateralis muscle during leg extension exercises does not differ significantly between sets performed to muscular failure and sets terminated 1–2 repetitions before failure, suggesting that maximal motor unit recruitment can be achieved without reaching complete muscular failure.

When muscles work hard during heavy lifting, they get tired from buildup of waste products and reduced energy supply. This tiredness forces the nervous system to turn on more of the strongest muscle fibers to keep pushing, even if the person stops just before complete exhaustion. The muscle fires just as hard as if it had gone all the way to failure, because the nervous system already activated every available fiber before failure occurred.