Zoning-In (Or Out?)

What is the reason for the “new” buzz around Zone 2 training, and why is everyone talking about it? Over the past months, I’ve been pondering this question as the emphasis on training at low to moderate intensities has gained significant attention. The benefits of such training intensities have long been recognized in the world of endurance sports. So, what has sparked the recent surge in interest? The catalyst appears to be Tadej Pogačar, or more specifically, his coach, Iñigo San Millán Head of Performance at UAE Team Emirates, and professor at the University of Colorado School of Medicine. In various podcasts, including an extensive interview on the ‘Drive’ podcast with longevity specialist Dr. Peter Attia, San Millán attributed Pogačar’s remarkable success to this particular training approach.

Even if the origins of this recent  Zone 2 hype tie back to San Millán and Pogačar’s success, there is still a broader context around the concepts of lactate threshold that play a pivotal role in optimizing training intensity that require examination.

Optimizing fat utilization is paramount for endurance performance, given the substantial reservoir of stored fat in the body, exceeding 25,000kcal even in the leanest individuals. Engaging in Zone 2 training cultivates a reliance on these fat stores, progressively raising the ventilatory threshold. The consequence is an enhanced capacity for athletes spending extended periods in Zone 2 to burn fat efficiently at higher intensities, preserving valuable carbohydrate reserves. 

While fat oxidation also occurs at higher exercise intensities too, the less demanding nature of Zone 2 allows for more extensive training, leading to greater adaptations. In essence, the enduring principle of ‘long, slow distance’ underscores its significance as a cornerstone in the training regimen of most endurance athletes.

LT1 or the First Lactate threshold marks the boundary between moderate and heavy exercise intensities. Below this threshold, blood lactate concentrations remain stable, while above it, concentrations may stabilize but at levels higher than baseline. Recognizing this physiological phenomenon as the “aerobic threshold” or “first lactate threshold” is crucial for endurance athletes.

Training at or below this first lactate threshold, often termed “conversational pace,” minimizes the buildup of acidity in muscles and blood. Athletes can sustain longer durations at this intensity, allowing for higher training volume. Many elite athletes adopt a pyramidal or polarized training distribution, emphasizing a substantial portion of their training below fist lactate threshold to enhance overall performance.

Putting specific numbers on Zone 2 requires personalisation, since each individual has slightly different physiology determining where the lines fall. It also requires you to know your threshold benchmarks and be confident they’re up to date and accurate. If we’re going to give  Zone 2 a special importance, we need to know for sure when we’re in it!

• The MAF Method: Phil Maffetone’s Maximum Aerobic Function (MAF) estimate uses 180 minus age, with adjustments for training status. Though not empirically tested, it provides a starting point for estimating fist lactate threshold.

• Heart Rate Monitor Zones – Most Sports Watches (Garmin, COROS etc.,) allow you to select one of three heart-rate methods:

  • Percentage of Maximum Heart Rate: Zone 2 is typically set to a default of 60-70% of MHR (Note that in the Drive podcast San Millán states that zone 2 will be about 70-80%).

  • The Karoven Formula: Also known as % of Heart Rate Reserve. Martti Karvonen’s formula calculates heart rates for different training intensities based on the heart rate reserve calculated as RHR + (%-Factor x (MHR – RHR)) where the % factor for Z2 is also 60-70%.

  • Percentage of Anaerobic Threshold (LT2) HR: Where Zone 2 = 80-90% LT2HR

[Note that wrist-based readings are not to be trusted especially in running and swimming where there is a high degree of movement]

As you can see methods 2 and 3 are much more aligned with the lab test than method 1 (which is what your watch will have as default). Interestingly if I were to use 70 to 80% MHR (as San Millán stated) rather than the “Garmin” default percentages for Zone 2, the values would line up well. I can only assume that the general average across the  “Garmin” population aligns better with 60 to 70% which is why it is used. Another data point from the Norwegian Olympic Federation referenced in Gordo Bryn’s Training Zone Essentials puts Z2 at 72 to 82% of MHR.

If you want to play with your own numbers you can use this Google Sheet – just save a copy and enter your values in the yellow fields.

Do we need to do a lab test or even worry about heart rate tracking?

The Talk Test: Identifying the first lactate threshold through the “Talk Test” involves exercising below the intensity where a comfortable conversation is possible. Research suggests strong correlations with physiological measures, making it a feasible at-home method.

DIY Talk Test Procedure:

• Choose a familiar 30-40 word paragraph.

• Wear a heart rate monitor.

• Start with an easy effort (keep this easy effort until you know it is stable this can take time!).

• Increase intensity every four minutes.

• Read the passage aloud during the last 30 seconds of each stage.

• Stop when you can no longer comfortably read aloud.

• Use the heart rate metric of the last stage as your first lactate threshold estimate.

How Relevant is it for You and Me? The 80:20 Debate

Aside from the scientific quibbles, the main objection from the amateur cycling world to San Millán’s paean to Zone 2 was that, while it may work well for pro riders like Pogačar (who train 20 to 30 hours a week), the rest of us don’t have time for unlimited amounts of low-intensity riding (or running or swimming). Pogačar’s mix of 80% low intensity (Zone 2 or below) and 20% high intensity is wholly achievable for a full-time athlete, but many coaches who train amateurs with full-time jobs claim that the 80:20 ratio doesn’t work for their clients. 

The eminent US coach Hunter Allen says: “Zone 2 is fine for pro cyclists. If you have five to six hours a day to train, then sure, go for it and follow the 80:20 mix.” It is less realistic, he suggests, for busy amateurs. “The majority of our clients have one to two hours a day to train. If they spent 80% of their training time in Zone 2, they would never improve the other things, in particular their FTP, which is critical to performance.” He is categorical in this judgment. “In fact,” he adds, “if they did an 80:20 mix, many of them would lose fitness.” 

According to Allen, time-crunched riders need to spend a greater proportion of their training time at higher intensities. “Zone 2 works for sure, but you have to have time for it. Riding more at FTP or at what we call sweet-spot, just under FTP, is a far more effective way to improve performance for people with less than 15 hours a week to train.” There is a related point here, which in fairness to San Millán he did point out during the Attia interview: for pro cyclists, because they are so well trained, Zone 2 is a higher level of effort, requiring a much higher power output than it does for most amateurs. Arguably, then, training in Zone 2 has a different effect on elite athletes – they are riding harder and faster at the same level of intensity

As the endurance world navigates the Zone 2 hype, understanding lactate threshold provides a broader perspective. The intricate interplay between training zones and physiological thresholds underscores the need for a balanced approach tailored to individual constraints and goals. Whether in the lab or through DIY methods, finding and incorporating lactate threshold insights into training can unlock the potential of endurance athletes.

Another Perspective – Start with the End in Mind

In Dan Bigman’s book “Start with the End in Mind” he takes the fundamental idea that success in sports (and even business and life) begins by envisioning the desired outcomes and then strategically working backward to achieve them. So rather than focusing on moving certain biological markers as employed by the scientists, could your performance goals be served better by having a different focus?

My main sport is swimrun. An event is a series of short runs below LT2 effort followed by lower heart-rate paddle/pull-buoy swims. In essence a long series of comfortably-hard run intervals with relative recovery on the swims. I know I can run well off swim training but I can’t swim well off run training – this shapes my priorities for training.

The backbone of my week is swim training with most of the volume at easy (Z1) and steady (Z2) intensity. On top of this, I incorporate some high-intensity sessions mainly to maintain economy/form and specific strength/force production. These are not heart rate zone-based power/pace as intensities above Zone 5 can not be gauged on heart rate. As mitochondrial density is regional, when I have longer events on the calendar I know I have to up the duration of the easy runs – pretty simple!

Be Your Own Best Coach

Unfortunately, there are very few First Principles in training physiology. Every coach has some kind of training system, but the better coaches do not apply their system in the same way with every individual they work with. Even if you have the luxury to share this responsibility with a coach, as a non-professional athlete you are unlikely to have the level of interaction where you can delegate the burden of this responsibility. Therefore you need to find a way to become your own best coach and not be steered blind by any single training philosophy. 

Remember, all models are wrong but some are useful!

Recommended Resources – Gordo Bryn’s Training Zone Essentials