Ok, I realize that my answer may not have made sense. I know fast-twitch fibers produce more lactate than slow-twitch ones, BUT apply the following excerpt from one of the above-linked articles to the situation where the fast-twitch fibers have been really trained and the slow-twitch ones haven't, and I'm working at a low gear/high cadence climb where I'm trying to enlist those small, undertrained slow-twitch muscles as my primary source of power: (Then I think it makes sense)

• Muscle fiber type composition. Slow twitch (Type I) muscle fibers produce less lactate at a given workload than fast twitch (Type II) muscle fibers. Although there is a big genetic component, proper training can influence the proportion of slow vs. fast twitch muscle fibers.
• Distribution of workload. A large muscle mass working at a moderate intensity will produce less excess lactate that a small muscle mass working at a high intensity. Certain cycling techniques will slow the overall accumulation of lactate by using different muscles.


So, the burn lets you know where you're struggling. And when you're new, you suffer frequently.