For those who are somewhat familiar with physiology and training science, this isn’t new. Two of the most performance-determining factors are your aerobic and anaerobic thresholds. When you've improved those threshold, you can work on other performance variables like fatigue resistance. But the better you know your LT1 and LT2, via for example a lactate test, the better your training plan will fit you. Let me take a closer look at those thresholds.

Aerobic fitness and LT1: your foundation

For convenience, I’ll equate aerobic fitness to your base fitness. This first lactate threshold, LT1, is a metabolic state in which no metabolic by-products (H+ ions) are yet accumulating in your body. It's an effort that you can sustain for a relatively long time. But your LT1 is more important than just an insight in to your “base fitness”. It also determines your recovery capacity and your ability to clear lactate, for example. The higher your LT1, the more robust your endurance is.

Anaerobic fitness and LT2: the red zone

Anaerobic fitness is the part of your fitness where you can run your fastest paces, and are going into acidosis, in the red. The downside is that metabolic by-products accumulate here, which means you cannot sustain the effort for very long. For those familiar with the terminology: you're relying on your anaerobic fitness when you're running faster than your steady state. By shifting this threshold, your sub-threshold pace becomes faster. That is exactly what you want when training for longer races: maintaining a high pace without immediately risking a complete blow-up.

How running zones relate to LT1 and LT2

When you translate those types of fitness into a metabolic context, they correspond to LT1, the first lactate threshold, and LT2, the second lactate threshold. This thresholds also have their place in training zones, a concept your might be more familiar with. Even more: these thresholds define your training zones. In training science, we often work with five intensity zones: zones 1 and 2 are low intensity, zone 3 medium, and zones 4 and 5 high intensity. This division allows us to introduce more nuance in training stimuli.

LT1 marks the end of low intensity and therefore the upper boundary of the well-known zone 2 I’ve mentioned before. LT2 is then the start of zone 4, beyond which fatigue increases exponentially.
These two thresholds move on a continuum from low to high intensity. On that same continuum you can add a second layer: the energy sources your body uses. On the far left you primarily burn fat (a virtually unlimited fuel), on the far right mainly carbohydrates (a highly limited fuel). To be completely accurate, I should add that you never use 0% of one and 100% of the other.

Training stimuli that move your thresholds

So imagine a line/continuum with two markings: LT1 and LT2. When we train, we try to shift those markings to the right. You want to be able to develop higher paces without having to “pay” more for them. On a lactate curve, this is called a rightward shift. The x-axis represents pace, the y-axis lactate/heart rate.

Certain workouts affect the first threshold more (endurance runs), others the second (most intervals). These thresholds can shift independently. Depending on genetic predisposition, muscle fiber composition, training history, body structure, mitochondrial biogenesis, … one of the two thresholds may be more developed than the other. In beginner runners, both thresholds are often closer together because general fitness is still limited.

How Trenara Applies Physiological Principles

A good training plan is therefore designed to understand and improve both lactate thresholds, because both determine your performance capacity and your progression. Thanks to the overhaul of our training plans this year, where we lean less on the dictatorship of data and algorithms and more on the physiology of training zones, we at Trenara have already taken significant steps toward letting these two thresholds evolve independently.

Because one of the biggest issue in the running apps industry is the fact that we over- or underestimate your thresholds. We have to base LT2 on performance data, not physiological data. And LT1 is almost always a fixed percentage based on LT2… and thus doesn't take the individual characteristics I mentioned above into account. Let's use a comparison between runner A and B to make it more clear.

And that opens doors to improve our approach… Keep an eye on our next feature release! ;)