Crucially, high mechanical tension is not strictly defined by the absolute external weight being lifted, but rather by the specific tension experienced by individual muscle fibers14. As a set progresses toward muscular failure, the body exhausts its smaller, endurance-focused low-threshold motor units14. To sustain force production, the central nervous system is forced to recruit dormant, larger high-threshold motor units—the muscle fibers with the greatest potential for hypertrophic growth14. As these final reps approach muscular failure, the concentric lifting speed involuntarily slows down, despite the lifter exerting maximum voluntary effort14. This involuntary reduction in contraction velocity is physiological gold for muscle growth: our muscles can only form a high number of force-producing actin-myosin cross-bridges when they contract slowly14. When a high-threshold fiber forms maximum cross-bridges and produces peak force, it undergoes extreme mechanical tension14. Thus, ensuring sets are taken within 0 to 2 reps of failure—where the bar speed visibly slows—guarantees that all motor units are recruited and subjected to the mechanical tension necessary to trigger the mTORC1 cascade14.