Mireya AciertoGetty Images If you’ve long been quickly trying to squeeze in as many reps as humanly possible before your muscles fatigue during a strength workout, you might want to literally slow your roll. There’s a new (-ish) strength-training practice to get familiar with that has nothing to do with speed, and everything to do with slow, controlled movements. Learn this phrase: time under tension (TUT). Trainers everywhere agree the TUT technique is one of the most effective ways of increasing hypertrophy, the term for increasing strength and muscle. “TUT is a type of exercise technique that aids in stimulating muscle fibers,” says Jessica Mazzucco, a New York City-area certified fitness trainer. “Instead of focusing on the number of reps of an exercise, TUT training aims to make athletes slow down and perform an exercise with less momentum.”