Basic Muscle Mechanics
Muscles and specifically skeletal muscles allow us to move maintain posture stabilize our joints and they even help us generate heat through shivering. There's three main muscle contractions I want you to know about and firstly all three muscle contractions involve you.
Flexing your muscle the first one is a concentric contraction. This involves the muscle flexed while shortening using the bicep as an example eccentric contractions. The muscle is flexed but now the muscle is lengthening. Then we have isometric contractions, again the muscle is flexed but it's neither lengthening or shortening.