We go to the gym to lift weights, but “lifting” is hardly the only portion of the repetition that counts. While telling someone you also “lower weights” doesn’t have the same sort of hardcore cachet, that portion of the lift—aka the negative or eccentric half—is also incredibly important. In fact, that’s where the real muscle-growth magic happens.

Let’s take a look at why and how both bodybuilders and strength trainers are using negative training to realize positive gains that have been documented by exercise scientists.

The Rise and Fall of Your Workouts

The focus of your workouts is normally lifting a weight, an action in which a muscle shortens. Whether you’re bench pressing or doing a biceps curl, the target muscles contract concentrically, meaning they shorten. Lifting a weight is also called positive-rep training.

On the flipside, when you lower the weight, the muscle lengthens, as the external resistance is greater than the force being supplied. This is also called the negative portion of the rep.

You’ve probably noticed that it’s easier to lower a heavy weight than it is to lift it. Normally, you control the speed of the negative rep, meaning you lower it slowly, but that’s usually just a long second, maybe two. In contrast, eccentric training requires you to really focus on extending the length of the negative rep to three seconds or more.

Muscles are capable of achieving a higher absolute force when contracting eccentrically—yes, it’s still called a contraction even though it’s lengthening— compared with concentrically. In fact, eccentric muscle action can produce 20-60 percent more force than concentric actions.