Muscle contraction is simply muscles doing work. So what’s with all these complicated terms?
Isometric contraction is what happens when you lift and hold a heavy weight steady. Your muscles bulge, but nothing’s moving.
Concentric contractions are movements where you exert muscle force, such as pushing a weight away from you.
Eccentric contractions are the opposite; it is when you lower / return a weight to neutral position, such as letting a weight come back down.
Think of the bench-press exercise, lying on your back: You start at the top and lower the bar; this is an eccentric contraction. Simply holding the bar steady without movement half-way down is an isometric contraction. Lifting the bar back to the top is a concentric contraction.
Now try to recognize these in your very next workout.