Your body has a precise capacity for processing energy, and knowing this capacity isn’t about resigning yourself to your limits. Instead, it’s the crucial first step to intelligently overcoming them.
The Protagonist: Lactate
For years, we’ve viewed lactic acid as the villain in our running stories—the monster that appears out of nowhere to weigh down our legs and extinguish dreams of glory. But lactate isn’t waste or toxic refuse. On the contrary, it’s a source of energy. It’s a reserve fuel your body produces when, during intense effort, oxygen is no longer enough to sustain the pace. Imagine it like the emergency candle you light when the power goes out: it allows you to keep going for a bit longer, but it has a limited duration. The problem isn’t with the candle itself, but when you light too many simultaneously. When lactate production exceeds the body’s ability to clear and reuse it, that’s when it accumulates. This accumulation leads to that feeling of unsustainable fatigue, that wall you feel like you hit when you demand too much from your body. The exact point where this balance breaks has a name: anaerobic threshold.
The Map
Knowing your anaerobic threshold is like having the treasure map to your athletic potential. It’s the boundary that separates a long-sustainable effort from one that will deplete you in a few minutes. Running “by feel” is perfectly fine; in fact, it’s essential for learning to listen to your body. But sensations can be misleading, influenced by the day, lack of sleep, or too much (or too little) coffee. Data, however, doesn’t lie. It’s the same difference as driving in an unfamiliar city by instinct versus doing so with a GPS. You can reach your destination in both cases, but only with the latter do you know exactly where you are and how far you have left.
How the Test Works
The lactate test works like this: you run on a treadmill, and the intensity is increased at regular intervals, as if you were climbing steps on a staircase. With each increase in intensity, a tiny drop of blood will be taken, usually from your earlobe or a finger, to measure your lactate concentration. Initially, the values rise slowly, like water gently warming on the stove. Then, at a certain point, you’ll notice a surge, a curve that rises exponentially. It’s like when water reaches its boiling point: for a while, the temperature rises gradually, then suddenly it starts to boil. That inflection point, that “elbow” in the graph, is your anaerobic threshold. A value expressed in speed, heart rate, and millimoles of lactate per liter of blood. Not the “average” for someone your age and height, but yours. Specific. Unique. Highly personal.
Okay, But in Practice?
Now comes the part that changes everything. What do you do with this number? You do a lot with it. That data is the key to truly personalizing your training, stopping the generic plans that work for everyone and no one. Knowing your threshold speed allows you to precisely calibrate all your training paces: Easy runs should be run at a speed and heart rate well below your threshold, to train aerobic endurance without accumulating unnecessary fatigue. It’s like building the foundation of a house: it needs to be done well, but without rush. Tempo runs are performed right around your threshold, or slightly below. This is the primary workout for raising the threshold itself and serves to teach your body to clear lactate more efficiently at higher speeds. It’s like training a muscle: the right stress at the right time to make it grow. Intervals set at speeds above your threshold help improve aerobic power and tolerance to very intense efforts. It’s like doing hill sprints: they prepare you for when the road truly gets tough.
Anyone Can and Should Do It
Many people think the lactate test is only for professional athletes. But if you have little time to train (i.e., if you live in the real world), knowing exactly what to do in that hour of free time three times a week is even more important. Running a lot without knowing what you’re training is like studying for an exam without knowing the topics. It’s exhausting and, ultimately, ineffective.
Another Level of Awareness
Doing a lactate test means looking inward scientifically. It’s understanding where the boundary lies between what you can sustain and what burns you out too quickly. It’s not just about performance; it’s an act of self-awareness. In short, it’s not a professional indulgence, but rather a tool to understand your real limits and train wisely. Because knowing where you are is the first step to understanding where you can go.