Chiming in on the Zone 2 Discussion

There’s been quite a lot of buzz around the topic of Zone 2 training over the past couple of years. Z2 exercise is recognized as essential for endurance sport performance, valuable for general health and fitness, and significant for longevity and functional independence. I thought I’d take this opportunity to share a few thoughts and observations.

Let’s begin with a general definition of the topic, which in this case is Zone 2 training. For the purpose of this discussion, we will define Zone 2 training as (relatively) low-intensity steady-state exercise which resides between the first and second ventilatory or lactate threshold at a blood lactate level varying from about 1.5-2.0 mmol/l. In this state lactate clearance is generally level with production and this remains relatively static through the exercise bout, as long as intensity is not appreciably increased. This type of exercise is heavily (but not entirely) reliant on fat-burning metabolic mechanisms.

During Z2 exercise, there are numerous signaling pathways which are at work. As previously mentioned, blood lactate levels have an effect. Heart rate, respiration rate, O2/CO2 balance, AMPK, PGC-1ɑ, and several other mechanisms represent the stimulus leading to adaptation. The systemic result of Zone 2 training is the enhancement of capillaries, enzymes, and particularly mitochondria, which are the energy producing organelles within the cells. The mitochondria are increased in number via biogenesis and upregulated to become more efficient at producing ATP (energy). The body consequently experiences improved delivery and utilization of oxygen, particularly in the working muscles. This is expressed as aerobic fitness and fatigue resistance. We typically classify this capacity as endurance. 

All training is valuable. For the Lifetime Athlete, every form of exercise, and the capacities they develop, are important. Body type, goals, and preferred sports will drive the choices and ratios each of us make, but we all know better (or should) to neglect any aspect of fitness if we are truly intent on playing the long game. You must have strength, speed, power, and agility along with your endurance. In varying degrees, yes, but no element should be entirely absent. 

Perhaps the two most significant aspects of Zone 2 training are that it is submaximal and volume-dependent. The submaximal component is unique. There are elements of cardiovascular fitness, especially VO2max, which are most effectively developed at higher intensities. However, the aerobic base, particularly in regard to fat metabolism, is best built at lower intensity synonymous with Zone 2. And because this is submaximal, it comes with less overall systemic stress and recovery demand. Thus, an athlete can do more Z2 work in general compared to higher zones and this is concomitantly required to optimize the adaptations.

My chiming in on this current discussion about Zone 2 aerobic training will be formatted as frequently asked questions and responses. The queries come primarily from Training Tribe members in The Lifetime Athlete App. My answers are a blend of known scientific data peppered with my observations and opinions derived from coaching and training thousands of people for over 40 years. I’m not claiming this is the definitive word on the subject – it’s just my viewpoint and I felt it was worth sharing. Here we go!

What is the inherent value of a zone-based model of training? Using a tiered model of output allows you to classify effort. It is certainly true that most human biologic functions do not operate with distinct lines of separation from one level to the next. Instead, there tends to be an almost seamless blurring or bleeding from one physiologic condition to another. That stated, the ability to quantify energy expenditure using a graded scale is useful for interpreting and communicating regarding exercise data. We can actually use forms of zone systems for all sorts of training, such as speed of movement and loads lifted. But zones are probably most popular and perhaps most useful when describing aerobic/anaerobic exercise, particularly when correlating with heart rate, blood lactate levels, and rate of perceived exertion (RPE). 

In very general terms, what is the most common zone system? You’ll see zone models ranging from 3-9 levels, but 5 is probably the most common. It’s the one we utilize most at TLA. The table below is a fairly generic example. In this particular rendition, I intentionally avoided any prescriptive/descriptive numbers such as specific blood lactate levels or % of MHR, FTP, and the like. Not to piss you off. Just to illustrate a broad concept in verbal format. We often use tables like this in our programming, and some clients actually do end up with very specific numeric values based upon extensive test data. But for our discussion today, I think this substantially reduces the possibility of confusion. Zone 2 is italicized.

Simple 5 Zone Model for Aerobic/Anaerobic Training

Thus, you can see that Zone 2 training builds endurance (cardiorespiratory fitness and muscular fatigue resistance) while developing the aerobic base. This is the foundation for efficiency with oxygen delivery and utilization during exercise and it improves overall health and recovery ability (both intraworkout and interworkout). It is performed at a relatively comfortable level using low-to-moderate effort. Most of the time this is a steady state type of training but you can also use low intensity interval training or repetition training. Intervals are not just for high intensity. They can (and occasionally should) be done at low to moderate output levels. 

Is Zone 2 a specific heart rate or range? Yes and no. I bet you saw this answer coming. The popular trend is to suggest that Zone 2 equates to a range of between 60-70% of your maximum heart rate (MHR). But honestly that range probably expands 3-5 beats (or more in extreme cases) on both ends based on fitness level and day-to-day variances within the organism. Very unfit or untrained individuals may be getting Zone 2 effects below that 60% threshold. And elite endurance athletes are capable of exercising aerobically and not producing much lactate at higher heart rates than us mortals. Your sleep and stress levels, as well as environmental conditions (hot, cold, etc.) can also shift things a bit. So the message here is, yea, training at 60-70% MHR is probably going to represent your Zone 2, but there can be occasional variances which must be considered, and respected. Many times you’ll be tempted to peg the high end of your range and lock in there. It’s actually better to float around the range until you find your sweet spot (you’ll know because you’ll feel it) and then hover there. We like to say “hover” because you don’t need to obsess about staying right on the number. In fact, overfocusing on what your device is telling you can be counterproductive. Consider tuning in to how you feel and telling your watch to go to hell.

Are zones predicted by watches and monitors accurate? Not very, in many cases. Or, said differently, the accuracy of most wearable-based predictive algorithms varies significantly from person to person. There will be some for whom they are spot-on. But for many others they are a little – or a lot – off. Yes, this is still true in 2026 despite all our modern technology. Don’t believe everything that’s marketed to you. You might be thinking that I’m down on wearables. Not so. I started geeking out with heart rate monitors in the early 80’s. Received a graduate degree that emphasized evaluating human performance in the laboratory. Got my first lactate meter in the 90’s. My position is that we benefit most when we use data strategically, as a guide which supports our intuitions and experiences. Being data-driven is good…to a point. But being an instinctive BEAST represents the world of the winner.

How do the zones correlate with the talk test? Incredibly well. In fact, that’s our favorite mechanism at TLA. RPE and respiration rate correlate strongly with intra-exercise conversive ability and this aligns within the Zone framework wonderfully.

Talk Test Table for Zone Training

The beauty of the talk test is that you don’t even need a training partner or coach. You can talk to yourself or even just think about the extent to which you could talk if you don’t want people to think you are jamming with your imaginary friends. It is incredibly accurate, costs nothing, and requires no time or cognitive demand.

Can you go too easy? That depends on the adaptations you are seeking. All movement is good and drifting in and out of Zone 1 and 2 is fine most of the time, especially if you are doing some easy, recovery-based training. From a health perspective, you’re getting most of what you need. But if your goal is to improve aerobic efficiency and build endurance, staying in the rhythm where you can’t deliver a soliloquy, but just a few choice rock lyrics or classic movie lines…is best. 

Will you ruin your aerobic system development if you creep up into Zone 3 during some workouts? This line of thinking holds to the belief that even a small amount of increased anaerobic output will negatively impact aerobic system development. While it is certainly true that your best aerobic base building will occur in Zone 2, relatively brief and occasional digressions into Zone 3 won’t hurt you. As long as most of the time you’re staying in Zone 2, you’ll be fine. The aerobic system is actually active during all Zones but it is the primary energy producer in Zone 2, when you’re emphasizing fat oxidation and staying below the crossover point where anaerobic metabolism picks up more significantly. Here’s a classic example. You are running or biking along and you come to a hill. You back off intentionally so you can try to keep your heart rate in Z2 as you go up. But even though you slowed down, HR still climbed into Z3 for a minute or so. Or, maybe you were feeling fantastic that day and just couldn’t resist attacking the hill, blasting over it, and then easing back to your endurance pace. Fine. No need to worry. 

Is Zone 2 all you need? In other words, can you get everything you need with Z2 and never do any Z3-4-5 training? Not necessarily. This relates to the last question and answer. Optimal conditioning benefits from and requires training that is performed in all 5 zones. Your lactate threshold, VO2max, and top end output all require purposeful training in Zones 3-4-5 respectively. It just needs to be done in the correct amount and ratios for your specific needs regarding goals, sports, seasons, conditioning level, and recovery abilities.

Does the neurologic system get involved with regard to motor skill development and mechanical aspects of the musculoskeletal system? Most definitely. This continues to be a frequently overlooked and disregarded area in training. The popular media leads us to focus on monitoring the zone, i.e. what’s happening in our bodies, more so than what our bodies are doing (form and technique). We must always remember that movement is a skill that is meant to be practiced. We should strive for it to be an art form more than a disaster scene. It is not uncommon to get a little lazy with regard to technique when effort/demand is relatively low, as in Z2 training. But a small amount of concentration and the occasional check-in during training is highly beneficial. We always want to teach our bodies optimal movement habits and avoid ingraining less effective or potentially injurious patterns. 

How do the concepts of economy and efficiency factor into this discussion? You are probably quite familiar with the vehicular analogy we often use in this context. Look at the sticker on the window of the new car at the dealership. Economy is miles per gallon. Efficiency is horsepower. As you move in Z2, smooth form minimizes energy loss. That’s being economical. As your fitness increases, you go faster at the same HR. That’s efficiency. Z2 creates this solid foundation which makes the higher zone training more effective. This is precisely why that foundation is called the aerobic base.

How much Z2 training is enough? This definitely depends on your goal. Are you seeking only your personal minimum effective dosage? Going after the max amount of training your body can absorb in pursuit of peak endurance sport performance? Those are different goals, for sure. The answer spans the gamut from as little as possible to get most of the long term health benefits to as much as you can recover from to achieve your ultimate fitness potential.

I used to speak often about the minimum effective dosage of exercise (aerobic in this case) because I was aware that a large portion of the genpop held that mindset. As in “how little can I get away with?” and related thinking. What happened over time was that I, and the people I was mainly working with, didn’t really care about that. We always thought “What do I need to do to get the best results possible? I don’t give a flying rat’s ass if this requires an investment of additional time and energy.” No kidding. It’s like that intro the announcer used to make at rock arenas, saying “You want the best, you got the best, the hottest band in the world…KISS!” Whether you were a fan or not, you get my point. 

But to be fair, let’s look at minimums first. The Physical Activity Guidelines for Americans suggests 150-300 minutes per week if you’re looking at lower intensities (and less if you go harder). One thing to keep in mind is that these recommendations lump together exercise training and general daily activity (GDA). That’s fine, as long as we stay focused on total weekly energy expenditure. 

Let’s say you’re a Lifetime Athlete and you train an hour a day, six days per week, doing a purposeful workout for which you “dress out.” This is your “official” exercise. Then you have a sport or passion pursuit (pickleball, hiking, etc.) that you do for an extra two hours weekly. On top of that you amass 5,000-15,000 daily step count equivalents (mainly in Zone 1) of GDA (chores, walking to mailbox, etc.). This represents our comprehensive model of organized training and activity which supports peak performance and longevity. Even though this volume of total movement comes in at around 15 hours per week, the amount of actual Zone 2 training in each person’s mixology could potentially be much lower than the 150-300 minutes the Guidelines suggest. Yet, few would argue that this model of training is somehow incomplete because of all the other necessary and important movement they are getting.

Or, you could just be an extremely active person. One who has an active job plus mows the grass with a push mower, splits and carries firewood, gardens with manual tools like shovels, rakes, and hoes, mops the floor (doesn’t have a Roomba), walks or bikes everywhere, etc. every day. Then your official training might only look like a little mobility and strength work for maintenance of the properties your lifestyle doesn’t quite fully address. This might not quite reach our TLA standards for performance, but the data certainly supports a similar outcome with respect to longevity. 

Getting back to that concept of minimum effective dosage of Zone 2 training, and using a weekly model, the Guidelines’ baseline is 150 minutes. So that could be a 30:00 aerobic workout, 5 times per week, or any other combination of sessions and durations that equals 150 minutes. Works fine for beginners or relatively sedentary individuals.

For Lifetime Athletes, my recommendation is to be sure to get 2-3 dedicated, steady-state Z2 sessions in each week, at a duration of 20-40 minutes, using the mode you prefer. You can certainly get some benefits from 10 minutes of Z2 training, but this seems to work best when you tack it onto a lengthier session involving other types of training. According to research, 20 minutes is better than 10 by a significant margin, as long as we are talking about staying in Zone 2 and not using higher intensities. 40 minutes yields most of the health and conditioning benefits for everyone but dedicated endurance sport participants. 60 minutes begins to get into the world of diminishing returns – at least for Lifetime Athletes who are not endurance specialists. Keep in mind, these recommendations only work if you are performing comprehensive, all-around training like that which we utilize in the Training Tribe.

I’m well aware that some of the current thought leaders in the longevity space suggest that you should do much more Z2 than what I just recommended. But everything has to be taken into context. If we look at the comprehensively-training Lifetime Athlete (the person every one of us is trying to be, can be, and should be) who has their lifelong sport built into their program, aerobic exercise exposure exceeds the Guidelines by far. If you go on a hike (or several) every week, which many of us do, you’re checking the Z2 box. And if you play a couple hours weekly (in total) of basketball, soccer, tennis, or any other highly active sport, you’re getting plenty of work done in Zone 2, 3, and probably 4 as well. Hell, if you play golf and walk 18…it’s all good.

There is also a very popular convention put forth by the same longevity gurus that you just can’t have too high of a VO2max and you really need to do a lot of training now to “build a cushion” for the inevitable decline which occurs in the later years. First of all, Zone 2 by itself isn’t optimal in bringing VO2max to its full potential. This requires additional strategic dosing of Zone 4 interval training. Practically everyone agrees with that statement. But one of the major problems is that much of the research done on VO2max levels in older individuals, and its rate of decline in those same people, has been almost exclusively performed on sedentary, relatively unfit subjects. Not Lifetime Athletes. The VO2max or metabolic equivalent task (MET) levels required for various life functions and daily tasks are well-established. So it is incredibly important that we have enough fitness in our later years for enjoyable participation in life as well as functional independence. My opinion is twofold. The aforementioned Lifetime Athlete model of training is more than adequate in developing maximal oxygen uptake. That’s why so much scientific study and experience underpins the unique programming we utilize in The Lifetime Athlete App. And Lifetime Athletes experience a rate of decline in fitness much more gradual than the general population upon which aging data is concentrated.

Lastly, at least on this topic of Zone 2 dosing, we have to appreciate genetically-driven individual differences with respect to body type. This is a subject about which I’m passionate and it’s the foundation of my book AnimalFIT. Humans are similar but we are not all the same. A retired NFL lineman is never, ever going to be a 2:10 marathon runner. And likewise, the recent champion of the Boston Marathon has absolutely no chance, even with the best drugs and training available, of getting a starting position on the O-line of either team in the Super Bowl. Ain’t gonna happen. Now, I realize these are extremes but that’s why I provided the example. There are some people who are naturally inclined to express aerobic fitness more easily than others. They have a certain body type and can generally outperform the average human in endurance and some aerobic power sports, often with very little training. But others have gifts of strength, size, motor skill ability, etc. that most aerobic beasts don’t possess. We all know this and that’s why we respect all the critters in the AnimalFIT kingdom. So the exercise prescription, or recipe for success if you will, must be personalized. Some folks don’t need much cardio to be healthy, fit, high-performing, and long-living. We all know a few of those dudes. [Note that I didn’t say they don’t need any cardio…just not as much as the next person.] But others definitely benefit from more volume of Z2 exercise with greater regularity. In the end, it’s more about what you’ve got (fitness) than how you got it. Just gotta have it.

Can you do too much Z2? Any good thing can be overdone, and the dose definitely makes the poison. However, the “toxic” effect of high amounts of Z2 is not overtly sinister. It’s more of a cautionary situation regarding orthopedic wear and tear from repetitive motion and/or supplanting other types of training. If you do a lot of running or cycling there is no denying that you are exposing yourself to a high volume of repetitive motion, generally straight-line and forward for the most part. There is a definite need to do enough supportive training that includes multidirectional competency, strength/speed/power, and positions/movements of “reversal” which utilize different patterns and muscle groups to offset the deleterious effects of same-same mojo. And when you really love your sport, and are driven to do a lot of it (and perhaps only “it”), you tend to end up not having enough time or energy for the stuff that keeps you balanced and ironically allows you to keep doing that one thing (running, cycling, etc.).

Another issue with excess in the Z2 arena is max training volume. I spent some years competing in endurance sports in the late 80’s and early 90’s. For a number of years I was able to sustain an annual average of around 15 hours of total training time per week. About 75% of that was Zone 2 exercise. But any time I tried to raise that volume in search of greater endurance, I tended to become chronically fatigued and needed to back off. I had discovered my personal limit for Z2 (and overall training) dosing. I’m sure this was affected by sleep, nutrition, work stress and all the usual things…but I had those dialed in to the best of my ability. So you can do too much. You just have to work pretty hard at it. Eventually, I got interested in other things and evolved into the model of training I’ve now used for over 30 years. It’s that Lifetime Athlete model we were talking about earlier. But if your goal is endurance sport peak performance, and you’re quite serious about it, know that you can do a hell of a lot of work before things start to crumble. You just have to be gradual about the process and build it into your lifestyle.

What about crossover effects from other types of training? These are both often overlooked and incredibly valuable. Many of your workouts, particularly those in the gym or on the athletic field (doing T2 summer workouts) will naturally involve multiple forms of training. You’ll do some warmup and activation items, some power and speed stuff, resistance training, a bit of HIIT or other cardio, and mobility work. Maybe not all this in every workout, but many if not most training sessions will be a spectacular mashup of athletic functionality. By design and by default. So, depending on what you’re doing and the amount of intraworkout rest breaks, your body is usually getting a low-level cardio stimulus. Even if you’re not doing dedicated circuits or aerobic machines. So, an hour-long workout that only contains 10 minutes of “intentional” cardio on the bike might actually have a Z2 training value of 30 minutes. Just an example and you can see how context-dependent this is, but as a Lifetime Athlete banging out solid work in the gym you get some incidental fitness bennies. This is admittedly hard to quantify but it’s definitely true.

How does cross-training (XT) affect single sport performance? Here we have an interesting conundrum. Alternative mode aerobic training allows you to decrease loading exposure from your primary sport. This is particularly true for runners who, for example, might do a little biking or swimming. In that sense, cross-training can allow you to maintain or even increase your overall aerobic training volume with potentially less risk of an overuse injury. But on the other hand, if you are trying to get good at one sport, it’s generally true that the more you do of said pursuit, the better (up to a point). This is known as the rule of specificity. Keeping a small amount of cross-training present most of the time is prudent. This keeps your body familiar with the XT alternative(s). Then whenever you want (or need) to pick up your XT it’s not a shock to your body. There’s definitely a seasonal aspect to all this and good coaching always helps.

Why is recovery the key to successful Z2 (and other) training? Instead of saying “do this amount of training to get such and such result,” you may instead want to ask yourself (or your coach) “how is my body responding to or recovering from the stuff I’m doing?” If the answer to that question is something like “quite well,” you are hitting your sweet spot or may even be able to increase your aerobic training workload if that is your goal. You can work up to training 15+ hours per week in endurance sports if that’s your jam. It just takes good program design and responsive adjustments. It’s fine to occasionally feel tired for a day or two, but chronic fatigue is a no-no for both performance and long term health. Go after your goals in fitness or sports. But always make sure you’re recovering well and feeling good.

Summing it up, Zone 2 training is good. We need it and should be doing it. But it’s just one part of the training process for The Lifetime Athlete.