Time under tensionTUT

Time under tension (TUT) is the cumulative time a muscle spends working during a set — a function of how many reps you do and how fast each phase moves.

It matters as one way of thinking about the growth stimulus, but it is easy to overstate: deliberately grinding out super-slow reps increases TUT while forcing you to use much lighter loads, which can reduce the mechanical tension that actually drives growth. It is a description of a set, not a magic variable to maximise.

In practice, a controlled tempo with a full range and a challenging load matters more than chasing a specific number of seconds under tension.