I have hurt my arm at the gym. i am restricted to do fast movements or pick up weights . how do i know if its strained?

Cramps or pain: If the involved muscles becomes very painful (minor soreness is expected after a strenuous workout) for more than a couple of days or muscle cramps develop, the muscle was too strained and you need to lighten up. Your body is giving you the signal that you may be doing harm to yourself.

Moderation: It is good that you exercise. You should titerate the time and intensity of exercise so that you are not too sore or too out of breath. You may gradually increase the rigor of exercise as your muscle strength improves. Have a healthy diet, exercise 30 minutes/day, drink plenty of water, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/.