On an emtb it is even more important to shift with mechanical sympathy, ie back off the power slightly when shifting. I have 1060 miles on the original chain and it's still only 0.4%. In my riding gear I weigh 92kg (203lbs, 14.5stone).
The chains are prone to breaking on EMTB's, it can take a slightly duff shift and a power input to do it, or just bad luck. I think I have snapped the chains on my emtb about4 time in the last couple of years