GCN and Zone 2

 

Two posts ago, I talked about my attempts to come up with a training plan to reverse the decrease in cycling speed I have been experiencing. In that post I said, with regards to my plan to cut back on long, slow rides in favor of faster, shorter rides, that I had the following concern: "... my slow training in 2021 was based on some of the most respected and widely accepted training advice in the cycling community, the value of Zone 2 training. Even to myself, increasing my speed seemed more like flailing than an upgrade." To address that concern, I am continuing to read and think about Zone 2 training.

[Brief Tutorial: The Intensity (e.g. how fast it is) of a bicycle ride is is usually described in terms of Training Zones, with Zone 1 being the easiest (slowest) ride and Zone 7 being the hardest (fastest.)]

Global Cycling Network (GCN) is an online cycling magazine which I have come to really like. When I have a question about cycling, they often have an answer that is comprehensive, clear, and plausible. I recently stumbled across a four part series they did on Zone 2 training that I found very helpful.

Part 1 was an interview with Iñigo San Millán, PhD, of University of Colorado School of Medicine. He is an exercise scientist and coach to a number of Tour de France riders, including the current wunderkind of cycling, Tadej Pogačar. I did a bit of research on his credentials and I was impressed. He talked about how the slow twitch muscle fibers which are developed by Zone 2 training are critical for supporting the fast twitch muscle fibers used during high intensity racing because they metabolize the lactate generated by those fast twitch muscle fibers. His bottom line recommendation is the same advice I have been reading from several other sources, that the optimum training schedule consists of 80% Zone 2 training and 20% training at higher intensity targeted to one's goals.

Part 2, which was narrated by GCN reporter Simon Richardson, was about how to identify your Zone 2. According to him,  heart rate and power are not good ways to do this, though they are useful for tracking zones once calibrated. Simon's definition of top of Zone 2, confirmed by Dr. Millán, is the point where fat metabolism plateaus. This is determined by measuring O₂ consumption and CO₂ generation during exercise.

The top of Zone 2 is also where blood lactate goes from flat to increasing. There is second level of lactate that is considered significant which is identified by a further increase in the slope of the lactate vs exercise graph and it is useful to describe these two lactate levels together.  As noted above, the first increase in lactate defines the upper boundary of Zone 2. The further increase in the slope of the line defines the upper boundary of Zone 4. Unfortunately, the terminology used for these two levels of lactate is inconsistent and therefore confusing. Even within this series of four videos, different terminologies are used at different times. Some of the names used for the lactate level at the top of Zone 2 are Lactate Threshold (LT), the first Lactate Threshold (LT1) or the Aerobic Lactate Threshold (AeT.)  Similarly names used for the lactate level at the top of Zone 4 are the Lactate Turn Point (LTP), Lactate Threshold 2 (LT2) or the Anaerobic Lactate Threshold (AnT or simply AT.) 

Both lactate and respiratory gas measurements require a laboratory. In the absence of a laboratory, breathing tests are the best measure according to Richardson. The top of Zone 2 where conversation is forced but possible and where one can breathe entirely through the nose. An alternative is to use Relative Perceived Exertion (RPE.) On the standard 6-20 RPE scale, the top of Zone 2 is 12.

Part 3 was both narrated by and focused on GCN reporter Manon Lloyd. (The picture at the top of the post is of Lloyd.) Lloyd had been an elite cyclist earlier in her life, but, in her words, she was "ten times as unfit" now had she had been back then. The premise of this and the next video is that she is going to use herself as a test case for the benefits of Zone 2 training. Besides the results of the experiment, we also get to see a state of the art version of how such an experiment is done.

Lloyd worked with the Human Performance Laboratory of the University of Bath in order to determine her fitness level at the beginning of the test and to establish her heart rate and power output at Zone 2. To do that, her blood lactate and breath O₂/CO₂ were measured every few minutes while she rode an exercise bike at increasing speeds:

Lloyd then met with her former coach to develop a six week Zone 2 training plan.

Part 4 reported the results of that training plan. The same tests were repeated and the results were compared to the results at the beginning of the test. Lloyd saw a significant improvement not only at the lower intensities around Zone 2 but at the high intensity zones as well:

I will go through these results line by line. LT (W) is how much power Lloyd could generate at her lactate threshold. At the beginning of the experiment, it was 140 watts. Six weeks later it was 160 watts. My estimate is this roughly corresponds to an increase in speed on a flat, windless road from 17 mph to 18 mph. LTP (W) (AP on the graph above) is the same value for the Lactate Turn Point and roughly corresponds to an increase in speed from 18 to 19 mph. It can be hard to accurately identify the points on the graph where these two increases in slope occur, and so sometimes these blood lactate levels are identified as absolute concentrations, e.g. 2 mM and 4 mM. The power levels at these two lactate concentrations is shown on lines 3 and 4.

The remaining four lines refer to VO₂peak. This is the more cautious, scientific version of the more commonly used VO₂max and for the purposes of this post, we can consider them to be the same thing. This is the maximum amount of oxygen an athlete can use and occurs near or at their highest level of exercise. Line 5 gives the ratio between the power Lloyd output at LT (the top of Zone 2) and her maximum power output. Line 6 shows the same thing for her power at LTP. Both of these increased during Lloyd's six weeks of training. The seventh line is the absolute value of VO₂peak itself. This increased by about 7% over the six weeks. The values both before and after training would be considered good but not elite. It might be expected that Lloyd could further increase this value with additional training. Finally, in line 8 we see that the maximum amount of power Lloyd could produce increase by about 12% over the six weeks. 

It is unsurprising that the Power Lloyd could generate at LT increased since that is the intensity at which she trained, but it is perhaps less intuitive that her power at LTP and at maximum power (power at VO₂peak) increased as well since these are levels of Intensity much higher than that at which she had trained. This is consistent with an article I posted about in 2021, a case study of an athlete who was having trouble increasing their VO₂max who, when he switched from the Zone 5 and Zone 6 workouts typically prescribed for increasing VO₂max to a three year program heavy on Zone 2, experienced a dramatic increase in his VO₂max.

Besides this four part series, I found some related articles from GCN, one on Sweet Spot training, one on Training Zone definitions, and one on Overtraining. The video on Sweet Spot training was the least useful, but I was pleased that the narrator, reporter Simon Richardson, suggested the same thing I had, that perhaps Sweet Spot training (training at the top of Zone 3 and the bottom of Zone 4) would be useful to cyclists whose time for training is limited. I noted that Dr. Iñigo San Millán was not featured in this video and suspect he would not have agreed. I found the use of training zones in the four part series to be inconsistent, so when I came across a video just about training zones, I had to watch it. The definition of Zones in this video was almost exactly the same as that used by Coach Hughes, which was comforting. The one difference was that Coach Hughes recommends Zone 6 for increasing VO₂max and GCN recommends Zone 5, claiming that Zone 6 is used to anaerobic capacity. That video credited Andrew Coggan as the developer of this 7-zone system, a fun fact I found of interest. Most significant was a third video which was again hosted by Richardson. This video consisted almost entirely of an interview of Dr. Iñigo San Millán. The topic of this video was overtraining. The symptoms of overtraining described in this video described how I am feeling right now with terrifying precision.

How did this series affect my training? As I note frequently, I try to limit the advice I take to one coach, Coach John Hughes, but Coach Hughes' advice is somewhat inconsistent when it comes to the value of training in Zone 2 and Zone 3. Thus, that balance is something I need to decide for myself. I go back and forth on this, and this series of videos pushed me back towards more Zone 2 training. However, the biggest impact on my training came from one of the three extra videos, the one on overtraining. Not that this video told me anything I hadn't heard before and it is not as if I were not wondering if I was suffering from overtraining even before I watched it, rather, it was more like perfect timing. I was ready to hear this message, especially because it came from a prestigious and credible coach and scientist. I let this message sink in, I watched it a second time, and then I decided to take a week off from training. This is not a violation of my determination to focus on Coach Hughes, Coach Hughes also recommends taking a week off from training at appropriate times. If anything, I had been taking off fewer weeks than Coach Hughes recommends. Thus, this video simply focused my attention on something I should have been doing anyway.

Some final, miscellaneous things I learned from this series of videos:

• Lloyd's coach noted that it is important that Zone 2 training rides be long in order to generate the stimulus needed to increased fitness. I have noted in the past that Polarized Training may be more about the lower end of that polarization (Zone 2) than the higher end. Similarly, I am getting the impression that it is the length of Zone 2 rides that makes them valuable.
• Decoupling is the well known phenomenon where heart rate increases at the end of a long ride with no increase in effort. For Zone 2 training, how do you handle that? GCN says when heart rate trends up, you should slow down to bring your heart rate back down. Coach Hughes disagrees. He says to maintain your speed and ignore your heart rate. I haven't decided what I think about this yet, but it is good hear the other side of the story.
• Manon Lloyd complained (as I have) that it is hard not to drift from Zone 2 up into Zone 3 when climbing hills. In the first place, it is comforting for me to realize I am not the only person struggling with this. In the second place, Lloyd's coach said 30 seconds in Zone 3 does not ruin a Zone 2 ride, so that within reason, hills can be ignored. Elsewhere in the series, however, it is noted that it is important to ride at a steady pace because it takes about 5 minutes to feel the intensity of a pace, so such drifts upwards should be kept short. GNC claims that if you do exceed Zone 2 for too long, it takes about 30 minutes to get back to the physiology of Zone 2 where you can obtain its benefits.

Implicit in this post is that I am reexamining my training schedule yet again. I plan to talk about that in more detail in a post in the near future. Stay tuned.