Why Going Too Hard Forces You to Slow Down: Lactate, Aerobic Capacity, and the Drain That Clogs

When I first started skimo racing, I started every race too fast. The gun would go off, I’d bolt forward, and for about 60 seconds I’d feel great. Then it was as if I was running through molasses. I’d have to slow way down, and the rest of the race felt horrible.

When I dug into why this was happening, the answer was simple: my aerobic base was too small. My aerobic system couldn’t produce enough energy to sustain the pace I wanted, so my body was relying on the anaerobic (glycolytic) pathway to make up the difference. That reliance came with an inevitable cost: a flood of metabolic byproducts that forced me to slow down.

This experience is common among endurance athletes at every level. Understanding the mechanism behind it explains why aerobic base training matters and why starting conservatively produces a faster average speed than starting aggressively.

What Happens When You Start Too Fast?

When you ramp up intensity quickly, your body recruits fast twitch muscle fibers. These fibers run primarily on glycogen (stored sugar), broken down through glycolysis. Glycolysis allows for higher speed and power output, but it produces lactate as a byproduct.

Your aerobic system has the ability to take up and utilize that lactate—think of it as a metabolic vacuum cleaner, sucking up lactate and shuttling it to muscle fibers that can use it as fuel. The larger your aerobic base, the bigger that vacuum cleaner, and the more lactate it can process. But if you produce lactate faster than the vacuum can clear it, the excess accumulates in your blood, raises acidity, and forces you to slow down.

By starting a race too fast, I was overwhelming my aerobic vacuum. The lactate flooded in faster than my system could clear it, and the only way to restore balance was to slow down dramatically—often to a pace well below what I could have sustained if I had started more conservatively.

Why Is the Recovery Pace So Much Slower Than Race Pace?

This is the frustrating part. Once you’ve accumulated excess lactate, the speed required to clear it is much slower than your maximum lactate steady state (MLSS)—the highest speed at which lactate production and absorption are in equilibrium. It’s often even slower than a purely aerobic pace.

The reason: even aerobic speeds produce some lactate. If you’re running at your MLSS, production and clearance are matched. There is no spare capacity to absorb the excess from your earlier burst. To create that spare capacity, you have to slow down well below MLSS, opening a gap between what your aerobic system is producing and what it can process. Only in that gap can excess lactate be cleared.

The practical consequence: if you start a race with a burst, your average speed for the entire event will be slower than if you had started without it. And athletes who are frustrated by the slow recovery pace often refuse to go slow enough, which prolongs the problem and makes the race even worse. Their takeaway is usually that they need more anaerobic capacity, when the opposite is true—they need a bigger aerobic base.

How Long Does Lactate Clearance Actually Take?

To illustrate, here is data from an anaerobic capacity test I performed. I set a treadmill to 25% grade and ran as fast as possible for about 60 seconds to produce maximal lactate. Then I lowered the treadmill to 1% and ran slowly, measuring lactate at several intervals:

My aerobic threshold for flat running is approximately 11 km/h (about 2 mM lactate). Normally, running at 7 km/h my lactate would be well below 2 mM. But after the maximal effort, I had to run far below my aerobic threshold to bring lactate back to aerobic levels. The clearance process took over 25 minutes of easy running.

In a race context, that 25 minutes of forced slow running after a 60-second burst would destroy your average pace. Starting without the burst avoids the entire problem.

Why Can Some Athletes Start Fast Without Paying the Price?

Some athletes can burst off the line near race pace and sustain it. There are two likely explanations, and often both apply:

They are highly slow-twitch dominant. Athletes with a high proportion of slow twitch fibers produce relatively little lactate even at high speeds. Their anaerobic contribution at the start is small, so there is less metabolic disruption to manage. The tradeoff: they typically have less of a finishing kick.

They have an exceptionally large aerobic base. A bigger “funnel”—more mitochondrial density, higher MCT expression, greater enzymatic capacity—means the aerobic system can tolerate a larger anaerobic input without being overwhelmed. These athletes have trained their vacuum cleaner to handle the load.

For athletes who are more fast-twitch dominant, the strategy is to start slower and ramp up gradually. The starting pace doesn’t need to feel slow—it just needs to be conservative enough not to overwhelm the aerobic system. The high anaerobic capacity of a fast twitcher is an asset, but only later in a race. At the start, it is a liability if used recklessly.

What Does This Mean for Your Training?

The lesson from this mechanism is the same one that runs through all of Uphill Athlete’s programming: your aerobic base determines the ceiling for everything else. A bigger aerobic system clears lactate faster, tolerates higher anaerobic contributions, and sustains faster speeds for longer. If you find yourself repeatedly blowing up early in races or feeling like you can’t sustain the pace you want, the answer is almost certainly more aerobic base training, not more intensity.

I learned this the hard way. Starting much slower allowed for a more gradual increase in lactate, and counterintuitively, a faster average speed. I also learned that to start faster in the future, I needed to train my aerobic system to absorb larger amounts of lactate—which meant more Zone 2 volume, not more interval work.