At lactate threshold intensity we can say we have recruited most or all of our slow-twitch fibers, and a good bit of our fast-twitch fibers, forcing them to adapt and become better at their respective roles. Finally, we can remain here for a long time, exposing our fibers to this workload and forcing them to adapt to meet it.
We summarize all of the above by saying that "Fitness is in the muscles." That is, a workout is nothing more than an opportunity to recruit a high percentage of muscle fibers, forcing these fibers to adapt and become better at what they do. As they become better muscles, they can do more work, the expression of which is "I go faster." We remind our athletes of this by including this phrase on our cycling and racing kit:
Work is Speed Entering the Body
Let's now talk about the real-world training implications of all of this:
Training Zones Determined Relative to Lactate Threshold (LT): Because lactate threshold is such a powerful place, we want to define our training intensities relative to LT. No big secret here, there are many systems for doing this, but hopefully our explanation above sheds more light on just why this is so powerful.
Zones 1 and 2: You're not really making yourself faster, at least not in a time efficient manner. If all you do is exercise at Zone 1 and 2, you have entire squads of slow-twitch and fast-twitch fibers that are never recruited, never forced to adapt. In other words, you'll get very, very good at riding and running very slowly!
Yes, you can get faster by riding and running a lot in Zone 1 and 2. However, in our experience, the volume required for this to happen, especially for cycling, is just not realistic or sustainable for the average age grouper.
Zone 4 (Lactate Threshold): Maximum exposure of all fibers to a training load, forcing them to adapt. At Zone 4, all of my slow-twitch fibers are recruited and forced to adapt; many of my fast-twitch fibers are doing the same.
This is a very efficient place to spend your training time because you get so many go-longer and go-faster adaptations. And not much time is required. For example, in our experience, as little as 40 minutes of LT work per week spread across your cycling can dramatically increase your speed on the bike.
Fitness Adaptations Occur Within a Range of Intensities: The either/or of aerobic/anaerobic exercise described by triathlon culture is simply not correct.
The summary of all of this is the Fifth Key: Pace/Power/Speed at Lactate Threshold is the Best Predictor of Performance.
That is, if we can improve your 5K, 10K, or half-marathon time, we can make you a faster half- or full-Ironman runner once we then put some endurance and durability under those faster running legs. If we can improve the speed at which you can ride for an hour from 19mph to 22mph, that similar speed increase will be expressed at 56 and 112 miles, assuming we put some endurance under it.
In other words, "a rising tide lifts all boats." We target, test, and track the "tide" of our athletes, as we know from that experience that fast at short is fast at long, once we put "far" under that "fast."
In Part III, we'll contrast the ideas and experiences we have shared with you in this series with commonly held endurance training myths.