by Tim Curry, MS ACSM-RCEP

Oh, The Drama!

Just like on the latest season of a hit reality show, academia has its fair share of drama. Admittedly, academic drama tends to be far nerdier and less TV-show-friendly as field experts debate data, theory, and interpretations of observations. You’re more likely to learn by paying attention to academic debate between field experts, and the drama is more nuanced. Over the past several decades one such drama has been unfolding in the world of exercise physiology specifically related to training. *Cue suspenseful music*…should endurance athletes purposefully spend time training in Zone 3?! *Record scratch* 

What is Zone 3?

Like any true academic debate, it can get a bit heated. Here are a few ways to think about Zone 3 (also commonly called Tempo or Medium Endurance):

  • Zone 3 can be found between the points where we leave lactate baseline and the point of exponential growth (aka lactate threshold), based on a lactate threshold test

  • Based on VO2max, it is the Zone between the two ventilatory threshold points

  • Zone 3 coincides with around 75-90% of power at threshold from an FTP test

  • A rating of perceived exertion of 3-5 out of 10 on the modified borg scale correlates to a moderate to hard effort of zone 3

  • Zone 3 is a pace at which you can talk (but not entirely comfortably) OR one at which you could listen in on a work call and follow the conversation, but you wouldn’t be a productive team member for the talk test

Zone 3 exists above the point where you are maximizing the usage of fat (Zone 2) but below the point where we begin to dump lots of lactate into the bloodstream (Zone 4). In Zone 3 our bodies are using a mix of carbs and fats to meet energy needs and beginning to utilize more fast-twitch muscle fibers. This leads to an initial increase in measured lactate, but at any pace within zone 3 lactate levels will eventually plateau vs. continuing to increase, such as what is seen after we pass lactate threshold.

What Is The Debate?

The debate could be summed up by two dueling models of training: the pyramid and the polarized models. 

  • Pyramid model - States that training time should be divided into 70% Zone 2 or below, 20% Zone 3, and 10% Zone 4 or above. If we were to stack blocks representing each of these training times it would look like a pyramid.

  • Polarized model - States that training time should be divided into 70% Zone 2 or below, 10% Zone 3, and 20% Zone 4 or above. This model generally views Zone 3 as a transition zone that must be passed through to get to Zone 4 and above. 

This change between allocated times by zone may seem trivial, but there are important implications based on what each group designates as the purpose of Zone 3. 

  • The pyramid model advocates for a percentage of time spent purposefully in Zone 3 for a variety of reasons, including that it’s where athletes race at for many (but not all) major events. Additionally, it’s argued that time spent in Zone 3 creates important physiological changes that produce greater performance compared to if zone 3 work was not included in training. 

  • The polarized model advocates for omitting purposeful Zone 3 work in training, arguing that it doesn’t create as much adaptation as Zone 4 (or higher) work and that you aren’t receiving the same benefits as dedicated zone 2 work. The argument is that zone 3 training time is better spent in Zone 4 and above to maximize performance gains. 

There is a lot of debate about how Zone 3 is set and measured in training. Both groups have pointed to professional training logs as data to support their model, even within the same group of pros! How is this even possible, and more importantly, what model should you choose for your training plan?

What’s It All Mean For You?

If the researchers and field experts can’t agree on this simple topic then what should the rest of us do? First, it’s important to understand that a lot of the focus for these models is on what professional athletes should do. These athletes’ careers live and die on a gain or loss of a tenth of a percentage of performance change, so everything little thing matters. Thankfully, there are still important lessons from the debate that can be applied to any endurance athlete. As an exercise physiologist and coach myself, here are the lessons I apply to training:

  • Both models are supported - We can use data from both for our own training plans

  • Spend 70% of your time in Zone 2 or below, and 10-20% in both Zone 3 and Zone 4+

  • Time spent in Zone 3 should be individualized based on the unique demands of the athlete’s event and their individual fitness levels

    • Moderate (1.5-3 hrs) or long (3+ hrs) events may benefit from more Zone 3 training, as this is the zone you’re most likely to be in for the majority of the race

    • Short (1 hr or less) and very short (minutes) efforts are less likely to require zone 3 work as you can sustain Zone 4 or above for these quick efforts

I encourage you to experiment with each guideline throughout a few months and see how they impact your fitness and performance. You may find that you prefer using one model for the early season and another for the race season based on what works best for you! Up next, explore Zone 4/5!

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