Training zones are a mess.

But there is a solution.

Training zones are artificial boundaries created by coaches and scientists to group similar intensities into a single category. This allows them to conduct studies and generalize how training is being performed and what effects different intensities have on the body. These zones offer practical applications in exchange for losing granularity, grouping different intensities within the same zone and placing similar intensities together.

For example, training zones are like school grades: we group people based on the year they were born, but in reality, someone born in December of one year is more similar to someone born in January of the next than to someone born in January of the same year.

These zones can sometimes cause more confusion than benefit, particularly for amateur athletes, as there are various models of training zones. Additionally, we often use the same name or number for different zones depending on the model being applied.

For instance, there's the 3-zone triphasic model, the Norwegian Federation's 5-zone model, San Millán's 6-zone model, Coggan's 7-zone model, and the new intensity domains, among many others (e.g., Couzen's, Pallarés's, Joe Friel's, Carmichael's), which result in +20 different models for training zones.

As you can see in the following graph, "zone 2," for example, represents an intensity between two thresholds if we use the triphasic model commonly employed in science, but it's below the first threshold in other models.

But it's even more serious: according to the Norwegian model, zone 2 is a relatively broad range of around 20 heartbeats below the first threshold. However, coaches like San Millán place zone 2 much closer to the first lactate threshold, while in Coggan's zones, zone 2 has nothing to do with lactate. Depending on the athlete, the upper limit of this zone may be above or below that threshold, as it is calculated based on their FTP (Functional Threshold Power).

To simplify this confusion of numbers, intensity domains were created to unify the terminology for each zone. Yet, these domains fall into the same trap of describing sensations, which creates ambiguity about what exactly is being referred to. For example, the "moderate" domain refers to an intensity that feels easy, while the "heavy" domain refers to a moderate intensity compared to higher speeds. The term "severe" domain isn't entirely clear, and some even speak of an "extreme" domain above it. However, one often experiences more effort in the severe domain (in intervals of 3-8 minutes) than in short intervals of 30 seconds to a minute, making the naming confusing.

Finally, we have the more physiological terms, which in my opinion, are the worst. The body functions as an integrated system, and almost no energy pathway works in isolation. Thus, any terminology related to oxygen-dependent or oxygen-independent energy production (mitochondrial, cytoplasmic), different substrates (glycolysis vs. lipolysis), or fiber types (fast-twitch vs. slow-twitch) also leads to problems.

Given that training zones are ARTIFICIAL categories created by coaches to simplify things and avoid constantly giving a range of watts or heart rates, I believe the most accurate approach would be to refer to them based on the perception of effort they elicit: "very light," "light," "moderate," "hard," "very hard," "maximum." This would be simple and useful.

However, given the problems I mentioned earlier with intensity domains, and to avoid further confusion (for example, someone could be working in the "moderate" power zone but feel an effort perception of 8-9 out of 10 after several hours of activity), I had the realization that all these problems could be resolved if we referred to intensity zones by colors. This would give us a fresh start where everyone agrees on what intensity each color represents, finally moving away from this endless maze of models and terminologies that only complicates understanding between scientists or coaches and adds no value to the training world.