Originally Posted by
RomansFiveEight
Push, suffer, hurt, sweat, cry, beg for mercy, do it all. But if you're at the point that you MUST stop, or you feel nauseous, light headed, dizzy, etc., then you've gone too far and you've actually slowed your progress down. I like the analogy of shutting an engine off at redline used above. It's hard on your body to stop suddenly during a harsh workout, and it can really slow down the progress of your muscles.
Once you're sufficiently fit, there really isn't such a thing as 'FAIL'. Your power doesn't go to zero and you fall over. Your body just naturally slows down so maybe a bit of semantics. I've felt nauseous on occasion when going hard after a period of relatively easy training. I don't think it's harmful in any way and it's difficult to injure yourself on a bike by going too hard as it's an aerobic sport so there aren't many explosive movements to damage muscles.
Short intervals <5m are generally more uncomfortable than longer intervals but they are also effective.