There comes a time when, in order to keep testing your fitness and get stronger, you're required to make your workouts progressively harder. In the gym, this might seem easy to do — equipment is readily available — but you might need to find other methods of resistance at home. Annie Mulgrew, founding instructor at Cityrow and NASM-certified personal trainer, told POPSUGAR that aside from adding weights, another way to up the difficulty is adding time under tension.
Using exercise bands and dumbbells, for instance, helps to add resistance, and in order to build resistance with just your bodyweight, Mulgrew said that you can perform moves with constant tension (which is one way of adding time under tension to an exercise, she said). She gave an example: "That means you're doing the eccentric action for three counts, you're holding the contraction for three counts, and then you're allowing the concentric action to also hold for three counts."
Eccentric movements occur when the muscles are lengthened and feel like they're under the most tension, and concentric movements are when the muscles are shortened. Picture a bicep curl: the concentric part of the exercise is when you're curling a weight up toward your shoulders, and the eccentric part is when you're lower your weight back down.
Mulgrew further explained that to have constant tension in a squat, you'd lower for three counts, hold for three counts, and take three counts to stand back up. You can do that for a push-up, bridge, reverse lunge, and more, she said, adding that it's also going to slow people down so that they focus on their form, which is another bonus.
If you don't want to perform exercises with constant tension, the most important part of the exercise to focus on for time under tension is the eccentric movement, because the longer the muscle is under tension in that way — aka the longer the muscle is lengthened — the more the muscle has to work (we've reported on that in the past). These movements build up muscle, and Mulgrew classified them as "slow eccentric exercises." Doing moves like a slow eccentriRead More – Source