Time under tension (TUT)

Time under tension (TUT) is the total time a muscle or muscle group is under mechanical stress during resistance exercise.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 131.} Some fitness professionals recommend 40 to 60 seconds per set for muscle growth, but research on that recommendation is limited.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 131.}

Time alone ignores load, so Zatsiorsky and colleagues prefer impulse, force multiplied by time, as a training measure.^{2Zatsiorsky, Kraemer and Fry, Science and Practice of Strength Training, 3rd ed., p. 218.} Helms illustrates the problem: if only time mattered, walking a marathon in ankle and wrist weights would build more muscle than an hour of hard lifting.^{3Helms et al., The Muscle & Strength Pyramid: Training, 2nd ed., p. 193.}

In practice

• Don’t drop the load just to extend a set: in one volume-matched study, squats at 35% of 1RM produced more TUT than squats at 70%, yet the heavier group produced about 25% more impulse.^{4Helms et al., The Muscle & Strength Pyramid: Training, 2nd ed., p. 194.}
• Superslow training taken to failure hasn’t beaten normal tempos for growth.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 131.} Traditional training built more muscle despite much less TUT, although the superslow group also used much lighter loads.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 131.}
• If TUT matters, it’s probably the total time a muscle works across the session, rather than the length of one set.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 131.}
• Sets and reps make a better everyday proxy: they also reflect range of motion, and few people time their sets.^{5Israetel et al., Scientific Principles of Hypertrophy Training, p. 48.}