There are three distinct phases during a lift. First, there is a muscle shortening phase or concentric contraction when lifting the weight (think of squeezing the muscle). Next, the muscle is lengthening under load to lower the weight back down - referred to as an eccentric contraction. Finally, there is typically a pause or isometric contraction between the two. The eccentric phase or slow lowering of the weight causes huge amounts of muscle damage and therefore spurs tons of new growth. To make matters even better, you’re stronger when lowering a weight than actually pressing one up meaning you can handle heavier loads on the lowering portion and cause more muscle fatigue. This all translates to negatives being a fantastic method for building strength and size.
Since negatives are extremely intense and can leave you sore for days afterwards, it’s best to start slow with only one or two exercises in your program. Using a spotter, load up your five rep max on an exercise (preferably a total body move like bench press). Perform the exercise as normal but take 5-6 seconds to lower the weight. With the help of a spotter, lift the weight back up. Aim for two to three repetitions.