acute joint/bone pains

My brother has been having problems with his joints locking up. I believe this is particularly occurring in his arms. For example if he punches outward, sometimes his elbow locks up midway, causing extreme pain. This also occurs when lifting weights. He can't lift very heavy weights, or he locks up and has extreme pain; he currently is trying to work around this by using two hands to lift a single 15lb weight.

He has stated that if his elbow 'pops', then he can continue lifting a weight for a while, but this 'popping' action apparently hurts a great deal.

What might this be caused by?

[edjones]

various other details: He is 17 years old. He uses a computer a lot, but doesn't sit in odd positions or cut off circulation along the arms. However, his hands are often cold (lack of blood flow?).

[abhijeet v ghosh]

hi jones,
well this is not a good sing what you are telling us. Locking up of joints on regular basis means there is some mechanical obstruction which is causing this problem.
I would suggest you to meet an orthopaedician and find out the reason.
regards