What is 'in a cast'? What is the atrophying of biceps? What is pumping iron?

[Sympathy]

After three months in a cast, Stan's biceps had atrophied somewhat; however, he was sure that if he pumped iron for a while he would soon build them up

Could you please explain this sentence for me?

What does it mean ?

What is "in a cast" ? What is the atrophying of biceps ? What is pumping iron ? What is build them up ? I don't understand a word.

Thanks

[Jamie (K)]

"In a cast" means that the doctor had put his broken arm (or broken something) in plaster so that it would heal. "Pumping iron" means lifting weights. You can find "atrophy" and "biceps" in a dictionary or encyclopedia. "Build them up" means to exercise and make his biceps big and strong again.

[Sympathy]

Thank you very much Jamie