Originally Posted by
fstshrk
It all depends on the intensity. If you are doing 400 miles a week in Zone 5, you are a prime candidate for Afib.
If you're doing 400 miles a week in zone 5 you've calibrated your zones wrong and and aren't a candidate for anything beyond perpetual mediocrity because you're working hard enough for your body to favor your lactate system instead of training your aerobic base but not hard enough to improve it.