The importance of time under tension
Everytime we unrack a weight we create tension. Our muscles contract and that tension is held for x amount of time until you can no longer perform a movement. The time you are under tension depends on the weight you use and your ability to handle it. And as you can probably guess the longer your muscles are under tension the more trauma/stimulus you bring to that area, hence why pushing yourself past the uncomfortable point is where the real growth is. So this means with your db presses you come down all the way, stretch the chest with no resting on the top, pushing back up, squeezing the chest then coming back down. Leg extensions you’re going all the way up, squeezing the quads and coming down as slow as possible stretching as far as you can right up until the stack is about to touch then back up. Eccentrically loaded paused deadlifts going down as slow as possible and right about a inch above the ground before you touch pausing then coming right back up. Performing the exercises this way will require a reduction in weight at first because of the consistent detail to tension but in time strength will progress with better results.