Long story short, I took some belly-dancing classes a few years back, and recently I've been following along videos with a friend of mine. I'm largely good, except for shoulder shimmies. Every time I do them at anything less than a glacier pace, I get pains in my pectorals, like sharp cramps that arc across the breastbone to either side. I don't think I have any underlying physical conditions that could account for this, and I'm in decent shape overall (although I will admit that pushups have never been easy for me). Is there any trick to avoiding such pain, maybe a way of exercising the right muscles to build up to it?