Everyone has their own routine when it comes to working out, including how many reps you do and how quickly you do them. If you're deciding between slow and fast reps, here are the benefits of each. Faster reps have the advantage of reaching muscular fatigue, or failure, more quickly, which is key to muscle growth. When doing fast reps, you also lift an amount closer to your max rep weight, which results in higher work volume (sets x reps x weight).
Slow reps are great for beginners or those working on their form since it allows you more control over the weights and your body's movement when lifting. When you go slow while lowering weights, you also keep more tension in your muscles and ensure that you're doing more of the work rather than letting gravity bring the weight down. Both types of reps have their benefits, so which one you use comes down to what you want to focus on during your workout.
Slow Reps vs. Fast Reps — Which is Better for Building Muscle? [PictureFit (YouTube)]