zepher and dabac, I just did the same thing to my 175mm XD-500T drive side crank last night. Luckily was starting from a dead stop when it broke. Double lucky because the 1 yr old and 3 yr old were in the trailer behind and I didn't go down!
Sure enough, shoe scuff marks on the cranks above and below where it broke. And I DO like to have my toes pointed out, so heel strike on the crank arm is more likely. Will be looking into some 3M anti-scuff tape for my crank arms because that's how I ride and how I like to ride. Thanks for the tip dabac.