If you're new to lifting weights, doing slow eccentric moves (like lowering a weight slowly) at a slow speed might build more muscle than doing fast concentric moves (like lifting quickly), but not more than slow concentric moves — so speed matters differently depending on whether you're lowering or lifting.

If you're new to working out and do leg exercises where you lower the weight slowly and quickly, doing it at a speed of 180 degrees per second might give you the biggest strength gains after 8 weeks — faster eccentric moves might just be the secret sauce for getting stronger.

If you're new to working out, doing elbow curls by slowly lowering the weight (eccentric) faster than you raise it (concentric) might make your biceps grow bigger than doing the same movement slowly or just lifting fast.

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