Lifting a weight 10 times is a kind of ISOTONIC contraction. Holding a heavy machine part steady while securing it in place may be categorized as ISOMETRIC contraction. Lifting heavy cans and putting them on a shelf may be called an ISOTONIC contraction. Flexing your leg muscles and holding the flex is an ISOMETRIC contraction. Lifting your heavy book bag several times is good ISOTONIC contraction.
Answer: Anxiety around crowds can happen to people who have issue's with claustrophobia. It can also happen to people who are not comfortable around a crowd of people. Being shy however, is different. People can be shy around a crowd of people, but they can grow out of it or they can make a change to not feel as shy.
I hope this is helpful. :)
