EccentricEccentric phase · Negative

The eccentric phase is the part of a rep where the muscle produces force while lengthening — lowering into a squat, letting a bar down to your chest, or the descent of a curl. It is often called the 'negative'.

It matters because muscles are strongest eccentrically, the eccentric contributes heavily to the growth stimulus, and it is the main driver of the muscle damage behind next-day soreness. Controlling it rather than dropping the weight is where much of a set's value lies.

In practice, lifters emphasise the eccentric by lowering under control over a couple of seconds; deliberately slow or overloaded eccentrics are a common tool for hypertrophy and tendon work.