Originally Posted by
Seattle Forrest
You should check your zones, for starters.
It sounds like you have a very powerful anaerobic system, but probably not as much aerobic endurance as you might want. I bet you're capable of explosive bursts, and they can actually last reasonable lengths of time, but they're for sure limited. Basically (you probably already know this) as you work harder and harder, your heart beats faster to supply your muscles with oxygen, until your heart just can't keep up with the demand, then your muscles are getting most of their energy from glycogen. They can't do this anywhere near as long as they can go with oxygen, and it hurts your legs after a while. You've trained this system to be very strong, but it's still time limited.
The point of doing Z2 rides is to improve your aerobic system, so that less of the energy for your rides has to be anaerobic. That lets you last much longer, run mostly on fat, and suffer less. In time you'll be putting more power out in Z2 and will/should go faster.
Group rides really aren't ideal for training.
My weekend group ride is actually a constant pace of about 17.5-18 mph average, which for most riders, is an all-day, century-type of pace. But in my case, it's an upper Z3 average HR kind of pace that puts me in fatigue land earlier than others.
This past Saturday I intentionally spent as much time in Z2 (and ended up averaging within Z2) as I could, put in 80 miles, and felt as fresh as I ever have over that distance. The only problem was, I was going so slow that anyone beyond the age of needing training wheels wouldn't have wanted to ride with me.