Slow vs Fast Reps. Which is right for me?

So you are taking a strength training class and you've heard me or your trainer, slow your reps down. But your goal is to achieve that "toned" look and you've heard fast reps with light weights. I'm confused! Which is best? Truly it will depend on your goals but let's break it down and see which is right for you.

Before we breakdown the difference between slow and fast reps, you need to understand that there are 3 phases of movement. There's the concentric phase which is the lifting phase, isometric phase which is the hold of the movement, and eccentric which is the lowering phase of the movement. Tempo is the speed in which you move through the concentric and/or eccentric phases of movement.