Lowering weights slowly makes muscle fibers longer, while lifting them quickly makes them thicker and more angled—both make muscles bigger, but in different ways.

If new guys lift weights for 15 weeks using only part of the movement—focusing on the shorter muscle position—they build more muscle size in that specific area and get stronger at certain joint angles, according to this claim.

If you're new to lifting weights, doing exercises where you lower the weight slowly (eccentric) might make your biceps grow bigger than exercises where you lift the weight up (concentric), after 8 weeks of training.

Whether you push weights up or lower them slowly, if you do the same amount of total work, your muscles grow about the same size.

Lowering weights slowly makes the connective tissue around your muscles rebuild and strengthen more than lifting does, helping your muscle adapt structurally.

Lowering weights slowly turns on different cellular signals and makes your muscle’s scaffolding change more than lifting does—even if both make your muscle bigger.