MariposasTime Under Tension (TUT)
Time under tension refers to the total duration a muscle is kept under load during a set, measured in seconds. Instead of counting reps, you're tracking how long the muscle is actually working. A slow, controlled set of 8 squats where you take 3 seconds to lower, pause for 1 second at the bottom, and press up in 2 seconds produces about 48 seconds of TUT, compared to maybe 16 seconds if you rush through the same reps. That difference in duration changes how the muscle responds, particularly the degree of metabolic stress and mechanical damage that drives adaptation. The nuance most people miss is that TUT is not automatically better when higher. Very long sets shift the stimulus toward muscular endurance rather than strength or hypertrophy, so the tempo has to match the actual training goal, not just feel harder.
Example
A lifter doing a dumbbell curl with a 4-1-2 tempo (4 seconds lowering, 1 second pause, 2 seconds curling up) logs 7 seconds per rep. Across 10 reps that set clocks in at 70 seconds of TUT, which sits firmly in the range many coaches associate with hypertrophy work. Compare that to the same 10 reps done in a casual 2 seconds each, and TUT drops to 20 seconds, a stimulus much closer to pure strength training.