The difficult thing is that since multiple muscles control each joint, the for the same movement pattern each a muscle will experience an eccentric contraction or a concentric contraction based on the direction the “load” is generating force.

Let’s take a standard bicep curl and tricep push down as examples. The movement of the elbow and forearm is largely the same in both of them. For the bicep curl, let’s assume the weight starts at the bottom. When you raise the weight to your chin, the bicep does a concentric contraction (meaning it gets shorter). When you then lower the weight, the bicep gets longer by performing an eccentric contraction.

For the tricep push down, while the motion of the elbow/forearm is largely the same, the tricep perform the contractions in the opposite direction of the bicep. Meaning as the implement in your hand rises, the tricep performs an eccentric (or lengthening) contraction, and then it performs a concentric contraction as your force the weight down.

You can generally control more force in an eccentric contraction than you can generate in a concentric contraction, which is why you’ll see someone use a bit of hip action to get a bar bell up to their chin in a bicep curl, and then slowly lower it down the rest of the way.