Concentric exercise involves muscle contraction with a load, while eccentric exercise involves muscle relaxation with a load.

“uh concentric is just a contraction of the muscle with a load um an eccentric is the relaxation of the muscle with a lot so when you're doing bicep curls when you're actually flexing the muscles with the low that's concentric and if you could only do that portion you'll be more beneficial than just lowering the weight back down because the muscle is still you know basically dense but now it's relaxing with the load”