I can assure people that cranks can and do break even when not under conditions of 'immense power'. My son had one snap cleanly near the B/B end - and he was merely pedalling along the A27 near Brighton...aulda said:Once, when cycling up the Col de la Bonnette, my crank actually snapped off! I put it down to the immense power I was generating to get me and my fully loaded panniers to the top. Fortunately, we were only a km or so from the top. However, it did mean then free-wheeling for about 30km to Barcelonnette and the nearest cycle shop. Luckily it was mostly down hill and for the flatter bits I relied on my brother to help keep my momentum up!
Fun, fun, fun.