Originally Posted by
Carbonfiberboy
Thus I know perfectly well when I'm in Z5 because I'm panting. If I'm not panting, I'm somewhere below that zone. In my 60s, I could reliably hold lower Z5 for about 10 minutes before I blew up. That's not all out, obviously. Back then I could hold all out for about 45", now it's down to 30" and the power starts to drop. I can kick harder than that of course, but can't hold that peak. If I'm training hard, I'll get an hour or less in Z4 and maybe 20' in zone 5 - over a whole week's rides, working as hard as I can recover from.
I'm definitely panting, breathing as deeply and quickly as I can in an effort I'm trying to hold for at least 15 minutes. My heart rate will be ~204 bpm.
If I push harder than that, I start to feel like I'm drowning and actually get symptoms of oxygen starvation or CO2 poisoning like being light-headed. My legs is probably starting to put more CO2 in the blood stream than my body can replace it with oxygen. There are cases of elite athletes passing out during an all-out sprint effort. They simply ran out of oxygen in their bloodstream and it can happen in colder temperatures. Obviously worse in high temperatures.
It gets worse when it's really hot so I definitely have to do the training indoors, away from the sun, strong fan, lots of cold drinks, and maintaining excellent ventilation. I'm 40 years old but my calculated Max HR might be way off, the closest estimate is 185 bpm but then I'm holding 204 bpm long enough so I suspect my actual MHR would be significantly higher, Maybe around 215 bpm.