I've also dropped my stem height 5mm and that's been enough to break me during a 100mi TT. I guess I'm running some limits closer than others and some body parts take longer to force into new positions than others. Also on the MTB I'll be moving around a lot more so fit is less of a factor. That and the fact that it's a relatively short ride for me. I reckon my arms will be fucked well before my legs. That's what usually happens. That or lower back from all the honking out of the saddle.
It depends on what it is and how hard I'm riding.
I've also dropped my stem height 5mm and that's been enough to break me during a 100mi TT. I guess I'm running some limits closer than others and some body parts take longer to force into new positions than others. Also on the MTB I'll be moving around a lot more so fit is less of a factor. That and the fact that it's a relatively short ride for me. I reckon my arms will be fucked well before my legs. That's what usually happens. That or lower back from all the honking out of the saddle.