Dr. San Millan's Z2 Rides

Hi there,

I listened with interest to the recent Fast Talk episode where Chris and Trevor spoke with Dr. San Millan about the physiology of the race season.

On the topic of the “foundation” or “base” for fitness, Dr. San Millan reiterated is advice that “zone 2” rides were the key to develop mitochondrial function (key to aerobic power, fat burning, lactate clearance, etc.)

My question is practical: what exactly is a Zone 2 ride?

Using my approximate number as a reference, in a five-zone model, my zones are as follows:

Z1: anything below 135 bpm. Depending on conditions and ambient temp, that could stretch to 250w.

Z2: 135-145 bon: comparatively narrow band, of anywhere between 240 or 250 w to 270-275 depending again on weather, temp, caffeine…

My VT1 is about 145 bpm.

In a three-zone model, all of the above is Z1.

Question : to get the best stimulus for adaptation from what Dr. San Millan refers to as Z2 Rides, do I need to ride in that narrow band of 135-145 bpm?

Is anything below that not intense enough unless I can string together very long continuous hours?

I ask because while riding @250w for two hours doesn’t “hurt” per se, it is still quite tiring, mostly mentally, as this is not an intensity that I would maintain without “intention”. It’s too hard to be an “easy” ride.

In short, where in the intensity and how much is necessary to achieve the desired goal?


Hi @CEBorduas, thanks for your question!

There are some other resources that you may have already seen, but will reference here for anyone who has the same question:

  1. Zones are a range, not a specific number
  2. 3 types of rides you should do
  3. How steady should your LSD rides be?

On to your questions about the zone 2 ride. When I was working with Dr. San Millan, we would set that upper end of zone 2 basically at your VT1/LT1, and it looks like that’s where you have yours set. From your sensations of a 2 hour ride at 250w, this would certainly still accomplish a zone 2 ride, but due to the amount of fatigue potentially built in, may be too high. With a narrow HR band, it’s completely reasonable to let yourself go into zone 1 during those rides. You will still get all of the benefits. You may, in fact, generate more benefits by allowing yourself to ride at that lower HR from time to time.

I would consider the entire band of <135 and up to 145 as your “base” range, knowing that for a 3-5 hour ride, you might realistically do 125-130bpm.

Not knowing your exact physiology or seeing your rides, it’s hard to say where exactly you should be riding, but from your original post, I get the sense that 250w for 2 hours is fine for 2 hours of riding, but not for longer base rides. Because of that, I would encourage you to work at a lower part of that HR range, allow the power/HR to drop into zone 1, and then build your time and effort from there.

As an example, here’s a “zone 2” ride from my training over the winter

You can see this labeled as zone 1, HR averaged 116 and power was 153w. EF of 1.33 and power:HR was 1.27.

Here’s another “zone 2” ride from just a week ago

This one is labeled as zone 2, HR averaged only 121, so not far from earlier in the season and still well within “base” (this was actually still my zone 1 HR range), but the difference in power was 33w with an average power of 186w. So this also shows EF of 1.63 and power:HR of 1.39.

This was done by taking the approach of limiting how far I push into the upper end of zone 2 early in the season and allowing the fitness to come gradually. It’s a long-term process (this was January through May) and I personally find that starting at the top end of zone 2/VT1/LT1 and expecting to ride at that intensity all the time is a mistake. I encourage those lower HR numbers as a way to allow for more rest from the hard stuff, and allow for low-stress base rides to be accomplished without energetically overloading the body. In terms of how much to do in order to achieve the desired goals, it’s really going to depend on the goals - you can achieve excellent results with 60-75 minute base rides. This will lead to a certain outcome (e.g., you won’t be competing in the P-1-2 category with that), and if you want a higher outcome, it will require more time. So that “how much” question is really a sliding scale, but my take-home message is that you can accomplish a lot of good adaptations from relatively little time spent at that base intensity.

Coach Ryan


OK maybe this is the “truly” dumb question. I see zones thrown around here all over the place and it is my understanding that there is no single definition of “zones” and how many there are? Dr Seiler proposes a 3 zone system, Dr San Milan, when he says zone 2 which set of zones (3, 5, 7, 9?) is he referring to? So I am trying to find a way to understand what we are talking about here without probably doing the digging necessary.


Hello I was wondering if you got a metabolic test to determine this VT1?

If so do you recall if you were burning mostly fat or carbs at this VT1?

Do you have a picture of the test of the fat/carb concentration through the test? If not do you have a csv or excel sheet you can send I can put in my software and come back with a graph. I do have a few ideas here but would need that data before I comment.


Hi Claude-Etienne,

I’m glad you enjoyed the episode! Zone 2 rides are that upper end of zone1 on a three zone model. So yes, it’s that narrow range just below VT1 to VT1. In your case that sounds like 135-145 BPM. And these are definitely rides you want to do by heart rate not power.

In terms of power, the numbers you have above sound too high. As you know, I’ve seen your data, so I’m not saying that as a guess. It’s really only in high level pros where you see zone 2 getting up around 275 watts. Personally, I’m happy when I’m in the 225 range.

And yes, there’s still value in doing lower intensity rides. Even though Dr San Millan’s zone 2 rides are done below VT1, they are still hard and take focus. They are not something you want to do all the time.

Hope that helps!

Good stuff, and this was a great episode. Really tied a bunch of concepts together.

one thing i thought was fascinating was the insight that mitochondrial function can degrade during the race season when you are just racing and recovering, in other words you lose ground in the endurance end, hence why zone 1 and 2 rides can still be important even when you’re sharpening, and/or you might take a race break to touch up the endurance every now and again.

The important tie in here i think is intensity distribution for amateur athletes. Because guess what, if i get out of balance–i.e., mitochondrial function degrades, my transporters that take lactate back in go away, something like that–i don’t have the option of hopping on a plane to the ballearic islands to do two weeks of daily 5 hour rides. AND i didn’t just spend two months doing daily 5 or 6 hour rides, because i didn’t have time to and was limited to the weekends. So because my ability to correct is so much more limited, i need to be more careful about keeping balance in the first place.

I feel like many amateurs balk at Trevor’s recommendations for intensity distribution in any training week because they’re like, first pros do more (so what’s te deal with this “polarized” nonsense) and second i myself can do more. And it’s like, well maybe you can, but what happens afterwards? Potentially what happens is maladaptation that takes months to correct vs. weeks because of your time limitations.

Another way to think about it is, because i can’t do a bunch of long sessions daily, in order to get as many easy sessions as possible in, i have no choice but to do them regularly


Yes, those HR numbers were taken from a lab test I had done at CU Sports back in 2019.

The power numbers were different because it was on my third day at altitude, but Jared (who did the test) was of the view that the HR numbers would translate to similar lactate levels at sea level.

I hear what @trevor says about my power numbers not being as high as previously posted.

All I know is that nowadays, on my Tacx Neo 2 trainer, with a 16-inch industrial fan angled 45 degrees at my torso, my power in ERG mode transfers about as follows over long periods:

118-125 BPM for 200-225 W
135 BPM at around 245 W
145 BPM usually not before 260-270+ W

For reference, when doing 8-minute intervals, I usually settle into around 335-340W for the efforts, which yields pretty linear HR with a slight increase as the workout progresses.

Hopefully these bits of info are useful to validate your ideas.

Let me know what you think!


Did a 2-hour ride that I hoped would be lower end of zone 2 on Swift today. It was rainy outside.

Numbers were as follows:

First hour and 20 minutes, average power of 255 watts, HR consistently between 130-133 BPM, so still below my 2019 Z2 numbers.

After 1h20 minutes, I could start to feel some discomfort starting to creep in and some mental erosion starting to occur. The effort wasn’t hard, but spinning at this intensity simply wasn’t pleasurable anymore. More like work.

Closing in on 2h, after I had emptied two water bottles, my legs felt like they were starting to fatigue. I could have gone on, but was happy to step off after 2 hours. HR was starting to drift, now just at the lower end of my Z2 range.

I know that @trevor will probably say my trainer is reading too high, but these Neo 2 trainers are known as very consistent and generally reading low, not high.

Not sure what gives, but had I wanted to be squarely in my Zone 2 HR range, then I’d have probably needed to crank it up another 15 to 20 watts. I erred in the side of caution, thinking that for longer efforts, this would probably be the right intensity.

Would I get any benefit from going higher up the range when time only allows for a 2h Z2 ride?


Do you have outdoor ride data to compare against? I know a lot of factors impact speed outdoors but maybe you could use it as just like a ballpark, sanity check, smell test type thing.

@BikerBocker When riding outside, I can never maintain an effort as linear as this. Even on the F1 circuit we have here (yes, we have one of those to ride on!), the winds are practically always so strong that the effort ends up being much more stochastic (VI typically at 1.1 or more) , and the HR average higher.

Outside, I basically shoot for a HR as best I can and let the watts fall where they may.

Only at threshold and above intensities on a hill does inside and outside correlate really closely for me riding in the conditions that are typical here.

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@CEBorduas was away for a few days off the computer.

Thanks for posting this.

Yes, this is perfect and the zones are exactly what I would use.

yeah i’m the exact same way. or well similar anyway, not exact: for lower intensity efforts i can keep my HR lower for the same power level on the trainer (and i think it’s as you said, about how on the road there are these little microvariations in cadence and effort that together add up), whereas for high intensity efforts my HR is usually lower outside.

I meant more, just ballpark, does your performance on group rides, races, strava segments etc. support a 270+ watt LT1? This is more to Trevor’s point that while the power is clearly high, he’s asking is it THAT high.

Riding and racing bikes in WA state i got the chance to ride with Tyler Farrar back when he was a moderately successful World Tour pro. He’d show up and race with us sometimes in the early season before his spring season would start. I say “moderately successful” not to take anything away from him; this was before 2010 and he had gotten some results but not his biggest results yet, and he was definitely a longshot whenever the big guns showed up.

Yet, alongside even very legit cat 1s and 2s, he was head and shoulders better than them, pretty effortlessly.


What I’m saying is I don’t really care what the number is outside. I keep to what feels moderate and try to contain HR under the ceiling I set for a given workout.

That said, on the trainer there are less variables and the numbers play out as I’ve shown above. I think it’s a valid question: why would I need to assume that 225 W is my LT1/VT1 number when I can ride 260 w with my HR just reaching into my lab tested z2 HR range, let alone far below the lab tested 147 BPM VT1 number?

I would like to better understand that. Not that I care what the ultimate number is, whether it’s high or low, or how I might fare up against a world tour rider.

Do the numbers follow HR or not? It gets pretty confusing!

well, fair enough, i suppose!

sorry, i’ll flesh this out a bit: apologies for overstepping, i had thought there was also a question about whether there was some trainer measurement weirdness going on, hence the recommendation to ballpark it. sounds like it doesn’t matter and in any event i meant no offense


When you say the zones are what you’d use: the HR or the power?

As you can see from my workout and Trevor’s estimates, it can mean fairly different things, and even different between outside or inside on the trainer.


None taken! Just trying to say: I’m a slow 43-year old, with no ambitions other than learn and get better. Ideally not waste my training time thinking I’m doing X when I’m in fact doing Z…

To me it’s OK that things play out different outside and inside. For what that’s worth, 225 watts feels much easier than whatever it would take inside or out for me to reach 145 bpm (ie, test LT1 HR).


Hi I would say the lactate, fat ox and heart rate all line up to where I would create zones.

Below is a pic:

Red being LT1 (fat max - I usuall like to see carbs as well here, I choose Highest fat with least carb) (steady endurance zone)

Purple being what I would call Tempo

Yellow being Threshold - in this case Lactate deflection as well as when Fat Ox goes to 0 for the first time.


Good conversation. @CEBorduas, I have no reason to question your trainer. I imagine it’s reading as accurately as you can expect a trainer to read.

In terms of your AeT heart rate and power, I will start by saying that these rides should always be done by heart rate. That said, there may be some value in getting your numbers retested. As fitness improves, both AeT and AT heart rate can go down. So, a 147 BPM VT1 may be too high at this point. You and I have similar max heart rates (as I remember) and my VT1 heart rate is closer to 135 BPM.

But I have two reasons to suspect that you are setting your power numbers too high. One is just the amount of training it takes to get VT1 power up to 275 watts for someone of your weight. You’ve told me how much training you’re able to do and it would be very difficult to get up to numbers like that with the time you have.

Second, and more importantly, is your description of your two hours riding at 255 watts. By your own description, you were starting to struggle at 1.5 hours and ready to stop at 2 hours. You were already experiencing cardiovascular drift by the end of that ride. That is not the description I would expect from someone riding at or below AeT.

To give you a comparison, if I went out to do an AeT ride, I would do 5-6 hours. The entire ride would be manageable and I’d experience minimal cardiovascular drift. Typical on a ride like that, I’d average 220-225 watts.

By contrast I did a ride two months ago on Zwift that I would describe similarly to your ride (manageable at first, but fatiguing and experiencing drift after several hours.) In fact, it wasn’t quite as fatiguing as yours because I rode four hours and didn’t experience drift until after the third hour. In the middle of that ride I averaged about 245 watts and 136 BPM for 2.5 hours. I considered that ride a sweet spot ride (and wrote about my frustration with the group going too hard in my ride description.)

You’ll notice that my average heart rate was still right around my AeT heart rate. So I could argue that it was an AeT ride but I know from how I felt and my response that it definitely was not. That’s the danger of going fully by the numbers.

Ultimately you have to make the call, but you and I are similar weight and we’ve ridden together, so you have a sense of how we compare. Do you feel you are 50 watts stronger than me?



A few things.

Let this not be a comparison. You’re stronger, no question. I’d still hurt you in a sprint, but that’s another story! :stuck_out_tongue:

I’m just trying to make sense of the objective stuff I see.

The ride was no struggle. Sitting statically for 2 hours is a struggle. Had I kept up for 4 hours instead of two, I suspect I would have drifted maybe another 5 BPM, still staying in the low 140s bpm at the most.

All I’m saying is here is the output I need to get my HR to places that resemble those plotted in my 2019 test.

I’ll do a 2 or more hours at 225 watts and I fully expect average HR to remain below 125 the whole way. That was still 12 BPM within zone 1 for me in that 2019 test, if BPM, and not power, is the indicator.

Jared had plotted my Zone 2 as between 137 at the low end and 147 (what he pegged as AeT) BPM.

Assuming 225 is my realistic AeT, how would my HR at that AeT workload have dropped more than 20 BPM in 2 years? Cause that’s the difference between 145 BPM and the less than 125 I’d be at on the trainer now working at 225 W.

All the while, my threshold HR feels like it’s in the same place as before (high 160s), and the power is also pretty similar, around 320-325 on the trainer, a bit more outside on a hill, and a bit less outside on the flat. I also see generally higher HRs outside.

Whereas threshold and plus efforts inside get difficult and painful as my HR reaches the mid and high 160s, the same efforts feel more manageable outside even where I see 5-10 BPM more at the same time.

So basically, not sure what to follow. Again, if @steveneal 's recommendations are that I follow the HR references from 2019 test, inside I won’t get anywhere near those HRs at 225 watts. Outside, it will depend on the terrain and the weather.

Happy to be a guinea pig. What would be a good test I could do on the F1 track? Prescribe me a test and I’ll do it in the name of a good case study!

not sure if it was just dumb but still no reply @trevor or @steveneal ?:

OK maybe this is the “truly” dumb question. I see zones thrown around here all over the place and it is my understanding that there is no single definition of “zones” and how many there are? Dr Seiler proposes a 3 zone system, Dr San Milan, when he says zone 2 which set of zones (3, 5, 7, 9?) is he referring to? So I am trying to find a way to understand what we are talking about here without probably doing the digging necessary.