Originally Posted by
DCB0
...I actually used to be able to break chains on demand as a demonstration for customers, and all I did was shift into the small chainring, hold the rear brake lightly while I shifted back and forth a few times on the rear while pedalling. I had 100% success rate for causing failures....
I must be a real lightweight weakling as I shift under load all the time on the road and mtbs and have yet to break a chain while shifting. I even shift while standing and pedaling, though not generally at max effort. This is with both Shimano and SRAM chains.