Hills during base rides

I have heard, that when doing a base ride, if my heart rate spikes above base into threshold because i ride up a hill, then the next half an hour cannot be counted as base riding.

Apparently i have awakened my anaerobic pathways and it will take 30 mins to return to aerobic only mode.

I believe that the aerobic mode vs anaerobic is more of a mix than a switch, but the question still stands:

Do i need to be paranoid about avoiding short heart rate spikes (say 5mins) during a base ride?

Great question! My first response is to ask if you need to select a better route for this base ride? It is acceptable to go out of range for changes in the terrain, but if a solid climb or on the more hilly side vs flat then I would suggest a new route if possible. The other piece to this is simply adjsting your “ego” and using the lowest gear (easiest pedaling) and “crawling” up the hill vs “powering” up the hill. I remind athletes of this all the time, there is a reason our bikes have all the gears they do these days. While there is a contribution of anaerobic capacity at those HR spikes it shoudl not be enough of good quality and TID of anaerobic activty to send the signal to your physio that this is what you are training. You can also look at the benefit of such HR spikes that are VO2/anaerobic related and incorporate these rides into your base training. I use this with athletes as “booster” rides in the mid-late base phase for the max aerobic benefits to your base fitness. Often it looks like 1x every 10 days during a true base phase. If your example here is jsut during the season and doing an “endurance” easy ride then go with what I suggested, if this is a base phase then you may want to look into adding a specific ride focused on intervals that get HR up to 88+% of max HR, these are durations of 2-4M or even doing some fun 40/20s where you go hard, near max efffort for 40s, then rest for 20s doing this for 8-13 intervals and doing 2-4 sets depending on fitness level. Hope this helps and happy training.