When duration matters: rethinking resistance training load through time under tension

Abstract

The traditional volume × intensity model in resistance training, defined as sets × repetitions × load, fails to account for the duration of muscular effort. This oversight neglects the importance of Time Under Tension (TUT)—the total time a muscle is actively contracting during exercise—which significantly influences hypertrophic, metabolic, and neuromuscular adaptations. Recent studies have demonstrated that manipulating repetition tempo alters muscle activation patterns, regional hypertrophy, and fatigue accumulation, regardless of total load. For instance, prolonged eccentric tempos increase muscle damage and protein synthesis, while faster concentric actions may enhance power. Furthermore, TUT provides a practical strategy for delivering sufficient mechanical tension using lower loads, making it particularly valuable for older adults, clinical populations, and athletes during deloading phases. Despite natural tempo deviations under fatigue—especially in later repetitions—approximately 70% of repetitions are typically performed with the intended cadence, supporting the viability of TUT-based programming. This viewpoint advocates for the inclusion of TUT in load quantification models and proposes a revised equation that integrates duration: Volume = sets × reps × load × time per rep. Incorporating TUT may improve the precision of training prescriptions, enhance individualization, and provide a more complete understanding of internal training load and adaptation.