Originally Posted by
mcjimbosandwich
At constant effort, see how much HR drift. I think it could be interpreted (barring things such as huge elevation changes, humidity, heat, etc) as a sign that the aerobic base is not strong enough.
I think it depends quite heavily on the effort. Riding at threshold for 20 min the HR will generally rise. I think you need to ride at an endurance or tempo pace for it to be meaningful. For longer durations I often get dehydrated which also make HR rise.