That could be another reason for it(in your shoulders/legs anyway). Lack of excersize can cause..erm, I dunno the term for it, but it's basically when your joints and whatnot "freeze" up. Which then when you try to move them, you can, but it'll pop/crack or whatever.
I believe it's called Overweightinitis. Horrible problem with America's youth.
I dod it a lot and yesterday my jaw started to hurt 
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