Zone 2 Cardio for Lifetime Athletes

Today’s topic is being presented secondary to popular demand. I frequently receive inquiries from our community regarding exercise selection concerning a variety of performance capacities. Recently, and extensively, Zone 2 Cardio has been at the top of the list.

The questions abound and they are very insightful. I’ll bullet them out and then address each one independently.

• Just what exactly is Zone 2 Cardio? 
• What is the value of aerobic fitness? 
• Should I use a monitoring device?
• Do I need to warm up for Z2 exercise?
• How much is enough?
• How much is too much?
• What if I’m an athlete in an endurance sport?
• Is there a way to tell when I’m fatigued?
• What mode of training is best?
• Does mixing modes negatively affect the training outcome?
• What if I can’t stay in Zone 2 while running?
• When should this training be performed?
• How does this work in conjunction with fed versus fasted training states?
• What about intra-workout fueling?
• How does Zone 2 training affect longevity?
• How consistently does Z2 training need to be done year-round?
• Can Z2 training interfere with my speed and strength goals?
• How can I get Z2 benefits if cardio is just not my jam?

But before I get to that list, I think it would be most appropriate to briefly describe how I’d like to approach this message today. Exercise physiology is a fascinating topic, and it can be fairly complicated if we choose to make it so. I have a graduate degree in this area as well as extensive experience doing laboratory and field testing on athletes using such parameters as gas exchange and blood lactate levels. My goal is not necessarily to impress (and bore) you with how much I know. But I also don’t want to dumb things down to the extent that they are extremely oversimplified and potentially insulting to the serious among you. So I’m looking for that middle ground that is true to science but also approximate enough for our community.

And, for the purpose of today’s discussion, I shall define our community as Lifetime Athletes. That label describes a broad middle under the bell-shaped curve of humans. Probably two standard deviations in each direction. Elite, competitive athletes in endurance sports (outliers) might leave this missive wanting more. And folks coming off the couch and just needing to get started by moving in a very general sense…may actually need less. But most of us, who desire to perform well at any sport and to have maximum health through the lifespan, should find this information at least very thought-provoking if not incredibly useful.

Put simply, Zone 2 Cardio describes exercise training that develops the aerobic base. This is also known as cardiorespiratory endurance. The ability to deliver and utilize oxygen at the tissue level, most specifically in the mitochondria of slow-twitch muscle fibers. To (more) easily supply energy to the body’s activity requirements and athletic demands without needing to do so with high reliance on anaerobic (glycolytic) metabolism. Doing more without producing much lactate. Burning stored fat for fuel and sparing our carbohydrates (blood glucose and muscle/liver glycogen) for high intensity outputs. Fatigue resistance. Workload tolerance. Repeatability. This is an essential foundation of fitness for all highly functional humans and that statement is even more true for anyone participating in an endurance sport. But don’t get hung up on that last sentence because Z2 training is valuable and necessary for every athlete and not just distance runners, cyclists, swimmers, triathletes, Nordic skiers, rowers, and the like.

If the baseline of aerobic fitness is relatively high enough (depending on the individual), more volume in any type of training can be supported. And since volume is generally the changemaker in any form of training, a higher workload tolerance is critical for increasing levels of performance. This condition is represented by unique adaptations in the organism. Increases in intramuscular capillary density, mitochondria (powerhouse or ATP-generating organelle of the cell), and specific aerobic enzymes occur. The body becomes capable of doing more submaximal work, at a higher level. In other words, the aerobically fit individual can do more easy to moderate output (sport, exercise, labor) in terms of duration than a lesser fit person. And, that same output will be at a relatively higher intensity (faster/heavier) as well. Additionally, recovery, between reps or sets within a workout, and between workouts themselves, will be more rapid.

You’ve probably heard of the crossover point. This refers to the intensity level during exercise when the energy substrate necessary to support exercise metabolism switches from primarily fat to mainly carbohydrate. This correlates with an increase in respiration rate and lactic acid production. As aerobic fitness or Zone 2 proficiency increases, the crossover point is raised to a higher heart rate, thus conserving energy at submaximal workloads and keeping blood lactate (and hydrogen ion) concentrations at levels which are more easily cleared. 

So where do the Zones come from? A little over 4 decades ago, heart rate monitors came on the scene. Coaches, trainers, and athletes began to classify, or “zone-ify” effort based on heart rate ranges at certain effort levels. They took some of the tried and true methods of pace and respiration rate and correlated them to percentages of maximum heart rate. Over time, this was synchronized with other measures such as lactate threshold (LT), maximal oxygen uptake (VO2max), and functional threshold power (FTP). Today, there are scales or zone models ranging from 3 to 9 different zones, with the 5-zone model being most popular. That’s also the one I use most often and prefer. More on that later. 

This is one of the places where I’m inclined to generalize a bit and I’ll ask my fellow geeks not to take me to task. There are a number of lab and field tests, some expensive and some free (with the exception of your effort), that you can use to determine such things as your max heart rate, lactate threshold, sustainable power, VO2max, and zone-specific heart rate ranges. Some of these tests use direct measurements and others employ extrapolations and calculations. I’m not going to get into any of these today. We’ll save that for another time. Instead, I’m going to share with you a simple table that I like to use with many of the athletes I coach. In very general terms, the table associates a zone (from 1 to 5), with a descriptive term for the fitness property each respective zone targets, and a corresponding “talk test” characteristic. The talk test represents the approximate level of communication you can sustain at each zone or effort level.

The zones are color-coded (blue-green-yellow-orange-red) for ease of coach/athlete data-sharing and communication and we use that color scheme in a variety of spreadsheets and documents. In this depiction, blue is very easy and red is “all-out” (or redline) for a given bout (in context with duration). As basic as all this sounds, it has been validated to be quite accurate in most situations. 

With this table, you’ll notice the glaring absence of Rate of Perceived Effort (RPE) designations, power ranges, or heart rates as they pertain to absolute max, lactate threshold, VO2max, etc. I have my reasons for these omissions. I’d prefer not to get too lengthy in describing those but you certainly deserve a little justification. 

RPE was originally based on the Borg Scale. This was a numeric scale ranging from 6-20 with descriptors from very, very easy to very, very hard. Each numeric rating was intended to correlate to heart rate when multiplied by 10. For example, if you rated your effort a “12,” your heart rate would theoretically be 120 beats per minute. There are a couple of challenges with this system. First, it is difficult to precisely determine one’s effort on a 15-point scale, and the arbitrary designation of  a max HR of 200 has the potential to be grossly inaccurate (just like the old “220 minus your age” method – secondary to individual variation). 

Consequently, over time, a modified 1-10 scale going from “very light” to “max” became popular. While somewhat simpler, this scale still has too many designations to be easily and accurately utilized in most exercise applications.

Condensing exercise intensity down to 5 zones of effort makes a lot of sense because we can roughly (key word here) line up each zone with a physiologic parameter.

1. Easy motion that is systemically non-taxing.
2. Exercise near but under the aerobic or first ventilatory threshold.
3. Training between the aerobic and anaerobic or second ventilatory threshold.
4. Working at suprathreshold levels to increase maximum oxygen uptake.
5. Approaching maximum anaerobic levels of output.

There are a couple points to note here. First of all, we can use a number of synonymous terms to describe the targets and effects of each zone. Second, it is possible to do a bit of hair-splitting and subdivide zones 3-5 to a greater degree. This is where the 6-9 zone models come from. However, I’m generally not in favor of this breakdown because in most cases it adds unnecessary complexity. The harder you go, the less you can and should think. Third, this scale adapts well to a number of popular metrics depending on athlete and coach choice. Such measures as % max HR, % VO2max, or % FTP are frequently employed. This representation is effective as long as those metrics are frequently assessed with good reliability and validity.

Now here’s the kicker. The zones are both nonlinear and dynamic, particularly Zone 2. You would be inclined to think that each zone would be of similar “thickness,” representing a heart rate range of an equal number of beats per minute. Here’s an example. Let’s say an athlete actually does have a measured, validated max HR of 200 bpm. Then let’s assume that each zone characterizes a 10%, or 20 beat increment. Hypothetically, the zones would look like this:

1. 50-60% of max or 101-120 bpm.
2. 60-70% of max or 121-140 bpm.
3. 70-80% of max or 141-160 bpm.
4. 80-90% of max or 161-180 bpm.
5. 90-100% of max or 181-200 bpm.

It is natural for the brain to be drawn to this configuration because it is organized and systematic. Unfortunately, it’s wrong. Genetics and training have profound effects on the zones. And this is especially true regarding Zone 2. Genetics can predetermine the starting point and “width,” in terms of beats per minute – of each zone. And consistent, effective aerobic training will expand Zone 2 “upward” as the athlete becomes more aerobically efficient. This raises the lactate threshold and makes more of this athlete’s work capacity possible via primarily aerobic metabolism. Z3, and to a lesser extent Z4-5 become “compressed” slightly.

I was an early adopter of heart rate training and I’m still a huge fan of the technology. But there are some caveats to consider. Even in 2024, if you want accurate HR data (who doesn’t?), use a chest strap. These are tried and true. The optical sensors on watches and wrist straps just aren’t  there yet. They have a tendency to be relatively inaccurate and inconsistent. I would assume that some of this has to do with how loose or tight the band is, the hydration level in your skin, tissue thickness, and the presence of lotions/residues…in addition to issues with the sampling technology itself. Regardless, until something changes, go with the chest strap. But employ that strap, and its associated watch or app, more as a consultant than a dictator. I will explain.

I’m always talking about the concept of instinctive wisdom. Some call it innate intelligence. All good. Let’s dive into that for a moment. The human being has what I call an inner beast. This is a brilliant, intuitive, sensing animal that has kept us not only alive, but thriving, for over 2 million years. In modern life we sometimes lose track of this a little bit. But with respect to heart rate training, we can develop a sense of “feel” that is both immediate and spot-on. Over time, while using a chest-strap HRM, an experienced athlete can feel, and estimate to within a beat or two, his or her heart rate during exercise. This is as amazing as it sounds astonishing.

I was also an early adopter of the TrainingPeaks App. Originally, it was geared mostly towards triathletes but the company has done an outstanding job of expanding the features to athletes (and sports) of practically any type. TP has a number of great workout analysis tools and it is an excellent coach/athlete communication platform. I have athletes that wear HRM’s on anything from a constant to frequent to occasional basis. As part of our coaching protocol, we will intermittently do a “blind” test in which the athlete’s device records and uploads HR data, but the athlete intentionally (honor system) does not look at it. Then we have the athlete estimate HR at several key points in the session and we compare those self-assessments to actual readings. This takes some reps and “tuning in” but it works incredibly well. 

You don’t have to use TrainingPeaks to be able to do this yourself. Just get into the habit of guessing your HR before you look at your watch. Getting proficient at this usually takes a few months because you need to experience all different types of workouts and readiness/fatigue states. Then, it’s quite easy to sync perceived HR up with actual…and talk test parameters (again, which have been proven to be valid). You become really adept at knowing your zones, especially Z2, during training. Whether you are wearing your device or not.

Related to all this, there’s an interesting occurrence I’ve brought up more than a few times on this platform. Modern wearable technology can give us a lot of data in addition to HR (even if not always supremely accurate) to look at. Heart rate variability, sleep duration and quality, training stress or workload levels, etc. I’m about to share a fascinating phenomenon and I kid you not – this has happened dozens of times over the years. I’ll be meeting with an athlete I’m coaching, usually in a videoconference, and I’ll ask “How are you feeling?” Immediately they will look down and say “Hold on, let me check my device and see what it says.” Then, without being snarky, I’ll say “No, that’s not what I asked you. I’m not inquiring about what your watch tells you…I’m asking how YOU FEEL!” Then we chuckle a bit and ponder the modern reliance on extrinsic information versus intrinsic knowledge. It’s good to keep this in mind when we’re talking about training zones.

Another pet peeve is the predetermined zones many devices will set up for you. Sorry, but the algorithms are somewhat insufficient in making very precise zone predictions. It works better to do some actual testing (that’s going to be another article) when you are “seeking the truth.” Or just use the talk test. I know, I know. Some of you will strongly resist this notion. How can something so seemingly generic like the talk test be accurate enough? So be it. I gave up trying to change people long ago. Just bear with me and try to keep an open mind as we go through this discussion. 

Regarding warmup for Z2 training…you don’t need much. You can just get rolling and settle into a rhythm fairly quickly. However, having said that, I like to use at least a small amount of warmup, prep, or activation for every training session. This is true whether the workout has a focus on strength, speed, sports skill, or endurance. Doing so invariably makes the session more comfortable, enjoyable, and effective while reducing injury risk. But with steady-state endurance training (Z2) in almost any mode, you can simply start the activity in Z1 and ease into Z2 when your body tells you that it is ready for a slight and gradual escalation. Pedal or row easily until you “feel it.” Walk, then jog a bit…before you run. Resist the temptation to just immediately “peg” your power, cadence, heart rate, or pace at the Z2 target.

This warmup wisdom is classic across sports and fitness. It’s related to Tissue Peripheral Resistance (TPR) and secondarily, collagen fiber extensibility. TPR basically describes the phenomenon in which it takes a few minutes for the body to figure out it’s going to be exercising for a while, and thus needs to vasodilate to allow for increased circulation and oxygen delivery. At first, exercise can feel a bit awkward mechanically and even slightly laborious from a cardiorespiratory perspective…and then it smooths out. This used to be known as “getting your second wind” as the body settled into exercise mode. That’s the sign that you have stabilized in Z2 just below your aerobic threshold.

Collagen fibers exist in all of the fascia, muscles, tendons, ligaments, and blood vessels. They benefit from a few minutes of very easy movement to allow them to increase in temperature and get lubricated. There is a traditional saying among elite Kenyan distance runners which can be loosely interpreted as “Let the run come to you.” When elite marathoners who can run 26 miles under 4:40 per mile start out at 10:00/mile pace, we mortals should follow suit. 

The warmup process is affected by environmental temperature and time of day. If you roll out of bed first thing in the morning, on a cold winter day, and start jogging down the road, your warmup will take longer than if you are jumping on your bike on a warm summer afternoon. 5-15 minutes is a very reasonable range to allot for warmup. Proper warmup, along with intelligent training progression, is one of the most important practices for preventing injury. And it is worth noting that there is good data to suggest that more cardiac abnormalities have been measured in chronic morning exercisers who typically use a hard, cold start. Join our community by becoming a member in The Lifetime Athlete App if you want to discuss that more deeply. We cover a lot of these types of topics in our Weekly MasterClasses and there is also a community discussion forum.

How much Z2 is enough? “It depends” is of course the answer and that prescription is based upon the responses to two primary questions. “Who is the athlete?”, and, “What is their goal?” I probably don’t need to mention this but let’s start off by recognizing that everyone is an athlete. That’s our mission and ethos at TLA. Helping everyone to discover, nurture, and embrace their inner athlete is what we’re all about.

I alluded to outliers or the extreme ends of the Z2-training population before. That’s a great place to start this part of the discussion. These “tips of the spear” can be described as athletes who need the absolute bare minimum of Z2 training for health, as well as those who need as much as possible.

Let’s start with the bare minimum crowd and attempt to define exactly what that is in the first place. This is a difficult and imperfect process to say the least, but let’s use the Physical Activity Guidelines for Americans. Those recommendations state that adults should get “at least 150 minutes (2-½ hours) of moderate-intensity aerobic activity per week, or 75 minutes of vigorous-intensity activity, or an equivalent combination of both, and should also incorporate muscle-strengthening activities on at least two days per week.” 

When it comes to older adults (65+), the recommendations keep the Z2 cardio and resistance training, throw out the high intensity option, and add in some work on balance and mobility with suggestions like Tai Chi, etc. 

I’ll start with a couple of critical comments about the Guidelines themselves. They were written using a variety of health-related data but also the expert opinion of the contributors. Fair enough. You gotta start somewhere. They redundantly use the term activity which I like to reserve for daily movement outside the realm of exercise, and more importantly, training. I imagine most of you have heard me discuss that distinction previously and how results in any outcome are best when one views oneself as an athlete who trains for a specific goal or performance. This makes exercise behavior more meaningful and purpose-driven. But that’s really just semantics so let’s keep going. 

The Guidelines reflect a bias, prevalent in some literature and certainly the popular press, that low and high intensity exercise are interchangeable and positive results can be attained as long as you get enough (the minimum effective dosage) of the mixology. On one level that’s true but on another, outcomes with training are specific to the methodology utilized. And with respect to Zone 2 cardio, if we replace it with HIIT, we will gain fitness but we will not develop the aerobic system to the same degree. There’s also a carryover effect to consider with many types of training. A lot of workouts will have you working hard, resting for various lengths of intervals, adding in some bonus stuff, setting things up, doing warmups and cooldowns, etc. Consequently, from an aerobic/anaerobic viewpoint, you’ll be dancing in and out of multiple (perhaps every) zones. So you do gain some aerobic fitness from almost any workout. You just don’t gain as much (and possibly enough) as you will in a dedicated Z2 workout.

So what I come up with regarding minimum levels, and this is based on decades of work with thousands of clients, is two summary statements.

• Anything is better than nothing. If the objective is getting an athlete (again, everyone) going, doing some safe training – and developing a love for the pursuit – shoot for consistency of habit first and worry less about specifics. Just have fun and don’t get hurt. With beginning (or restarting) trainees, results will come fairly rapidly no matter what they do.
• When you’re ready to dedicate some of your training focus to Z2, get 2 hours per week, and do this as 30 minutes, 4 out of 7 days. With a little give and take fudge factor in there. That’s entirely adequate in a comprehensive conditioning model, which also includes training in the other capacities. Those are strength, speed, power, and agility. And agility does not just include mobility and balance – it blends mobility, stability, reactivity, and fluidity. 

Everything in training should flow. One element should blend, bleed, and blur into another. Progression should be relatively gradual to allow for ideal adaptation and to avoid injury and breakdown. Thus, a half hour of Z2 cardio, 4 days per week, probably would not be the starting point for true beginners. They’d work up to that, preferably with good coaching. But it is an outstanding goal for baseline.

There will be some who will balk and say “that’s still a lot.” My only response would be maybe, but I don’t make up the rules of biology. Aerobic fitness trains up fairly rapidly, but it also detrains faster than the other capacities. Accordingly, we need to keep our cardio habit quite regular for baseline maintenance. I like the two hours a week, broken into 4 x 30 minutes for two major reasons. 

1. It’s very approachable from a time perspective and efficiently provides a Z2 benefit.
2. The system we employ at TLA is comprehensive and also incorporates other forms of training as well as significant amounts of general daily activity (GDA).

I’m sure I’ll get some flack for that recommendation. Where and how did you come up with that? If we go back to that broad middle in the general population, and exclude rank beginners and elites, 4 x 30 has seemed to be the sweet spot for many Lifetime Athletes. As long as proper intensity is observed, and recovery is adequate, 4 days are better than 3 and 30 minutes are better than 20. This amount of training creates enough fitness to raise the aerobic threshold (even if only slightly) and create a more enduring human athlete. It also improves health markers with respect to cardiovascular and brain function. You certainly can do more and you will become more fit. But you won’t necessarily get healthier than what you’ll achieve at the 4 x 30 level.

This 2 hours (on average, throughout the year) of weekly aerobic training fits into our system of 4-6 hours of total (comprehensive, multi-capacity) training per week. There will be periods when we are emphasizing strength or speed and the aerobic volume will be less. And during our Endurance Block, the cardio goes up. You could argue that a teenage sprinter or 20-something lifter needs no aerobic training, and should just put all their training eggs into the primary basket. I wouldn’t argue with that. But when we start to think about mature(ing) humans and training to be a well-rounded athlete for life…the resistance to regular cardio tends to abate.

There’s a line of thinking that’s been in vogue for the past 20 or so years. It’s the argument that time is precious, we modern humans have so little of it, and we need to do the most brief, efficient forms of exercise possible. As in…”What’s the most efficient workout and what’s the least amount of exercise I can get away with?” An inquiry into the minimum effective dosage of exercise training. I’ve had an interest in that concept for a long time and have developed some models in accordance with the literature. However, I don’t fully agree with that approach and my thinking about training volume continues to evolve. I must admit I was driven to explore that concept because many people don’t like exercise and are really looking to get it over with as fast as possible. My feeling is that’s because they just haven’t had the ideal positive experiences with enjoyable, results-getting training that is not punitive in any way but is a joyous celebration of movement and life. So my focus is honestly more on what’s best for human health and performance more so than the bare minimums. Life is indeed too short. But time spent training is a gift in and of itself as well as an investment whose returns are documented to be more life-enhancing than any other lifestyle or pharmaceutical intervention in existence.

What if you play a field or court sport, like soccer, tennis or basketball? You’ll definitely need less dedicated Z2 cardio because of that carryover over or cross-training effect, but I still like to have a little in the program for these folks. That might look like 2 x 20 minutes in a given week, and probably via low-impact modes secondary to the ballistic nature of many sports. I’ll say that any athlete who is a regular sports participant can trim back their non-sport cardio exercise, but they still benefit from a little aerobic base (and recovery) training.

Now let’s swing the pendulum all the way to the other end. Let’s consider serious, high-level, competitive endurance athletes. Technically, any event that lasts longer than about 2 minutes in duration is primarily dependent on aerobic metabolism for peak performance. But we’re mainly talking about athletes who are into sports that are considered distance events. Runners, triathletes, Nordic skiers, rowers, backpackers, cyclists, and the like. 

Historically, the training for these events has evolved to be based on high volumes of Zone 2 training. Of course, in competitive athletes the other zones are also utilized strategically in program design, but the majority of training for the most successful athletes is rightfully biased toward aerobic system development. 

Related to the volume of training, I’d previously mentioned minimum effective dosage. Well, serious endurance athletes need the other end…maximum absorbable dosage of Zone 2 cardio in order to squeeze out the full potential of the aerobic system. In this case maximum should be defined as the highest level of Z2 cardio training that yields benefits but does not compromise necessary training in Zones 3-4-5 or other types of supplemental conditioning such as resistance and mobility work. And absorbable means it should be recoverable as in not causing systemic or orthopedic breakdown. 

While you can increase aerobic fitness in a beginner or detrained individual in a matter of weeks, the more advanced an athlete is…the longer it takes. We’re not talking months or years here. It’s actually decades. While not infinite, the aerobic system has the capacity (somewhat genetically pre-determined) to increase fitness significantly. As you would imagine, this definitely reaches the territory of diminishing returns in that elite athletes sometimes pile on additional hours upon hours of weekly aerobic volume just to squeak out half a percentage point in improvement. To those at the highest level, it’s totally worth it. Especially if that’s how you are making your living. 

Patience and consistency are determining factors in most areas of life and not just training. However, aerobic system development is definitely one of those areas where keeping the training regular and being patient with the process is key. One of the great challenges with endurance athletics does not actually reside in the cardiorespiratory system. The issue is with the musculoskeletal system. Bones, joints, muscles, tendons and ligaments adapt to the stress of training. They just do it much, much more slowly than the heart, lungs, and blood vessels. High volumes of repetitive activity can be a recipe for the disaster known as overuse injury and this is manifested as a variety of “itis” conditions in the connective tissues as well as stress fracture and cartilage erosion. 

Thus, what would seem very simple on the surface becomes quite complex with deeper inspection. You would think (and rightly so) that just piling on the volume in Z2 training would be sort of easy. Actually, this is where very artful coaching comes into play. The program has to be designed to fit the unique athlete. What is the rate of progression and how is the overall training plan periodized? What are this particular athlete’s specific needs for recovery? Are there any technique or mechanical flaws that need to be addressed? How much in-sport training can this athlete tolerate versus alternative mode cross-training? How is the immune system doing? As you can see, keeping an endurance athlete healthy is no easy task and it’s extremely important to be comprehensive in the approach as goals, performance, and training volume increase.

But at any level above absolute beginner, each of us can decide how much training we can support in pursuit of our goals. There is some trial and error here and you need to see what fits into your lifestyle and schedule. As long as you are having fun, staying healthy, achieving goals, and not getting injured…the sky is (almost) the limit. You do you. Just get a good coach. Doesn’t have to be me and you can always coach yourself. Find what and who works best for you. 

There are both instinctive (subjective isn’t the best word here) and objective ways to tell if you are fatigued as it relates to Z2 training.

You are no doubt very familiar with being kind of tired, lethargic, and maybe a little sore. We’ve all been there. But if you get rolling in your workout, and the warmup isn’t really happening, those sluggish symptoms aren’t going away, and you’re feeling no better or possibly a little worse…your body is telling you something. It’s not a great day to do the planned session. You will benefit from cutting back to a little Z1 and hitting some light mobility work and calling it a day. Or maybe shutting it down entirely if you feel awful. Training only works on a relatively fresh and recovered body, and it’s during the recovery phase when our bodies are busy making the adaptations. Don’t force it and don’t feel guilty. Take a look back a day or two ago and see if you overdid it. Also, check your stress, sleep, and nutrition levels.

On the objective side, you can assess your readiness, or the appropriateness of training on any given day, by looking at your heart rate response to exercise. If your resting pulse is high, your effort at a given pace or output seems greater than usual, and your exercise heart rate is not climbing into the target region…you’re tired. The body has sort of a “governor” which discourages you from messing yourself up. You should heed this and not try to cognitively override because someone suggested that’s just weakness of character or lack of mental fortitude. This is the opposite situation from being fresh, when resting pulse is low/normal and HR quickly jumps into the desired zone as you begin exercising. Live to fight another day. 

There’s another term which you’ve probably heard known as cardiac drift. Let’s say you are doing a steady-state cardio workout. You started out and the effort felt fairly comfortable. You established a pace or heart rate that you felt was at the upper end of Zone 2 and were motoring along. However, as time passed, your heart rate began to drift upward, 4-8 beats per minute for example although this could be higher. That’s because you slightly overestimated your Z2 ceiling and you were accumulating a blood lactate level just above threshold. In a case like this, you would back down into a lower HR range (lower than you started) to finish the workout, start the next one at this range, and make sure it doesn’t drift up. Retesting your zone limits (another article) may be indicated. Cardiac drift also occurs when heat, dehydration, and fatigue enters the picture during longer workouts or races. It takes more and more effort to maintain the same pace.

We’ve covered overreaching and overtraining before but here is a quick reminder. If you have subtle difficulty swallowing and notice your (lymph) glands are possibly swollen, you are overcooked. Shut it down and hit the steam room, sauna, or cold plunge. Or all of them. Or maybe just the couch with a fuzzy blanket.

The mode of training that is best is the one you use in your sport. For example, if you are a runner…run. Cyclists should ride. And so on. If you don’t have a dedicated sport (yet), just pick the mode you like the best and which feels most comfortable for your body. The reason we encourage endurance athletes to do most of their training in sport mode is because, in addition to those physiological effects we’ve been discussing, there are unique neuromuscular and musculoskeletal adaptations for each sport. In this way, the body really gets good at doing the very thing we want to be good at.

Now, having just said that, we sometimes have to offload the body a bit so we don’t break it down. I like to mix in some uphill walking, stairmaster, elliptical training, cycling, and pool running with runners. Reducing impact and eccentric contractions in this population can be useful from time to time. Sometimes a cyclist benefits from getting off the bike and using a rower or stair climber. Nordic skiers are great cross-trainers, using hiking, running, cycling, and rollerskiing to their advantage. Swimmers mainly just swim and that’s partly due to the nature of swimming and the variety of strokes available. What we’re talking about here is cross-training, or alternative mode aerobic training. This is not supplemental conditioning which includes resistance training, mobility work, etc. That needs to be done but it is not a substitute for aerobic modes of training.

Mixing modes has no negative effects on your aerobic system development unless you are a very focused endurance athlete in a single sport. Again, in that circumstance, you only want to cross-train enough to prevent injury and put most of your Z2 effort in your primary sport mode. Get all the bennies you possibly can. But for the rest of us, mixing modes is extremely beneficial because it spreads the stress of movement around different patterns and positions. This inherently reduces injury risk and also works on not just durability but versatility in The Lifetime Athlete. 

If you are locomoting (walking, jogging, running) and you’re not very aerobically fit (no shame in that) you may notice that you can’t keep your HR in Z2 when running. It may creep up into Z3. In this case, it’s very wise to downshift to a super-slow jog, or just walk. Establish the locomotive “gear” that keeps you just under the aerobic threshold and celebrate it. Just cruise along at that comfortable talk test level and enjoy the workout. Stay consistent over several weeks or months and you’ll soon be jogging and running without bumping into Z3.

Z2 training can be performed at any time of day or at any point in your workout. Pay attention to getting a good warmup if you are doing aerobic training at the beginning of a workout or first thing in the morning. As we mentioned earlier, your warmup needs will be less in the afternoon and practically nonexistent if you are hitting your cardio at the end of the workout. From a general fitness standpoint, you can (and it’s probably good to do so) mix up the placement of your cardio. But, if you have specific goals, you may want to prioritize the components of your training session for optimal outcomes.

This leads our discussion to the concepts of primacy and recency. With primacy, you do what’s most important, early in the workout (just after warmup). If you are prioritizing strength, speed, or power development, do those first when the body, and CNS, are freshest. In this case, save cardio for the tail end of your session. A serious endurance athlete would do the opposite. Recency can be interpreted as saying the CNS remembers most the thing you did last. For this reason, if you have some sports skills you are trying to tune up, it’s a great idea to practice them towards the end of the session. A classic example here would be shooting 100 free throws after basketball practice.

Fasted cardio is the practice of doing your Z2 training on an empty stomach, usually in the morning prior to consuming breakfast. Over time, this can enhance fat utilization and aerobic efficiency. It may also assist with fat loss body composition goals. Like anything, experiment with this and work into it gradually if you are so inclined. 

Training in a fed state, essentially by undertaking a session in close proximity to a pre-workout meal, is another option. For most day-to-day cardio in isolation, this usually isn’t necessary. But if we are looking at the context of the cardio training being a portion of a 60-75 minute workout, this can be useful. Pre-workout feeding may also be valuable prior to a long run or ride. However, I like to reserve most pre-workout feeding for high intensity sessions, in which the carbohydrate demand will be higher.

Intraworkout fueling is the practice of ingesting nutrition, usually liquid carbohydrates (but not always), during a workout. This is most useful in longer sessions over an hour and lasting potentially much longer, as well as during competition. Intake should be approximately 30-60 grams of carbohydrate per hour in a 7-8% solution, per American College of Sports Medicine Guidelines. This is of course with some room for individual variance due to gut tolerance and food/beverage preferences.

The topic of longevity is often an elephant in the room when we start thinking about Zone 2 cardio. Arguably, genetics are the most powerful driver in longevity. Additionally, lifespan may have more to do with what you don’t do than with what you actually do. In other words, we can and certainly should avoid such practices as poor sleep and nutrition, drug and alcohol abuse, etc. Few would argue that those things have the potential to shorten a lifespan. But how much a certain practice can add years to your life, or at least allow it to go “full term,” is more difficult to quantify. We know that regular Zone 2 training improves mitochondrial function, cardiovascular and brain function, glucose control and other metabolic parameters, immunity, and energy levels. So it certainly improves quality of life. And it probably also enhances length of lifespan. Aerobic training might let you live longer but it absolutely will help you to live better. Worth pondering.

Consistency is king when it comes to training. We say that a lot. But we are actually stating that in relative terms. As in, be regular when it comes to training, but afford yourself a little flexibility in exactly what you do throughout the year. You never really want to completely abandon a capacity (strength, speed, power, agility, endurance) for very long. It’s very effective to emphasize one of those components for a season or block of training, and keep the others at a maintenance level. Then change it up. There is a lot of science and art in designing well-balanced programs. You can push one capacity and then allow your body to recover and maintain while you emphasize another. These applications can be very distinct or profound…or they can be quite subtle. As long as you are always at least touching on your aerobic system…you’ll be fine.

One of the things we have to remind ourselves about fitness or performance capability is that having it is what actually matters. How we achieve said ability isn’t important. So as long as you possess adequate (or your goal level) aerobic fitness (and strength, and speed, etc.) it doesn’t make much difference how it was attained. Training is a means to an end. We shouldn’t be slaves to a schedule or workout, but instead should view training as a tool we employ to accomplish an objective. There certainly is a gain in mental toughness when we do hard things. Completing a challenging task in life is gratifying and that’s true in training as well. There will always be a place for such elements. But I have seen “doing fun things” which get results –  impact intrinsic motivation, consistency, and outcomes –  to a greater degree. Keep the joy of movement in the training plan. Decide how seriously you want to take yourself.

Interference gets talked about from time to time and it’s worth mentioning here. In the context of training for different capacities of performance, the question is this: “Will doing Zone 2 cardio negatively affect my speed, strength or power?” I’ll begin with a reassuring statement and say probably not. 

The thinking behind the concern regarding interference revolves around training stimulus. Because Z2 cardio targets aerobic metabolism and slow-twitch muscle fibers, it is facilitating adaptation in those elements. The reasoning continues that such a bias would compete with explosive training and adaptation and impair the development of speed and power. The only way this scenario would potentially be true and problematic is if program design was inappropriate. To clarify, if you took a speed-power athlete (sprinter, linebacker, etc.) and did an inappropriately high amount of aerobic endurance training which displaced the volume of speed-power work necessary for peak capacity, performance would be impaired. But that doesn’t happen because these athletes prioritize explosive work and (with good program design) only do (or should do) small amounts of low-impact cardio to support health and training. In the same manner you wouldn’t think that taking a marathoner and having her do nothing but heavy lifts and sprints would lead to a PR on the race course. Interference isn’t a factor at the elite level because those athletes just don’t train unscientifically.

You actually have to do a LOT of one thing before your body sees this as a message to ballast the other capacities and focus only on becoming the best at it. This is by default the definition of the elite, serious, competitive single-sport specialist. Coaching and program design in these cases have to very delicately handle the training so that the athlete can not only hit that 97+% of potential, but not get wrecked in the process due to the loss of other capacities becoming rate-limiting factors. That’s why we have off seasons to shore up issues that come out of the peak season. No high-level athlete tries to maintain peak season all year long. It’s ironic that many recreational athletes attempt to do exactly that. 

Some examples may be beneficial. Powerlifters, football lineman, and other athletes who use very compressed, sagittal plane states in performance spend time in the off season working on regaining some of that lost mobility and movement variability that was a result of the peak season. By restoring this function they can improve joint health and reduce the risk (high in this population) of hip and knee replacement surgery. Many other athletes, like runners, cyclists, tennis and basketball players, etc. hit the weight room to rebuild some muscle and strength. Doing a lot of one thing is the key to becoming the best at it. But in the advanced athlete, we need to always be bringing them back into balance in order for them to have a long and successful athletic career.

The rest of us, the broad middle of Lifetime Athletes, don’t need to worry about interference. As long as program design is good, we’re just not doing enough cardio to mess up our strength and speed. That stated, it is important to look at your body type and goals…and make sure your training system lines up accordingly. Another pitch for some good coaching. Most of us just want to feel good and move well. To be capable of good, all-around performance across a wide variety of sport, recreation, and fitness pursuits. We can tweak training to almost infinite degrees to make it work for our unique, and evolving, bodies.

We’ve made it to the final question and I’m actually quite surprised we went so deep. It’s like we got rolling on all these great inquiries and now I’m waking up from a trance. Quite a few folks will share that they just really aren’t into cardio, especially single-mode steady-state training. Particularly if it is indoors. I can relate to that. I love going out for long hikes or bike rides and that is so enjoyable. But plop me on a stationary bike, even with some audiovisual programming, and each minute feels like an eternity.

Quick side note. Nobody asked about this but it just occurred to me. Is it bad to use programming and dissociate (as opposed to focusing in and associating on your effort) during Z2 cardio? Not at all. Because Z2 requires a low level of concentration, it’s fine if you’re distracted. But if you are hitting Z4 VO2max intervals…skip the earbuds.

Back to making indoor aerobic training more tolerable and enjoyable. Mix the modes. Do a “Cardio Combo.” How you do this is up to you, and dependent on what you have available, but here are a few suggestions. 

In honor of the season, try a trinity. That is, do 3 different machines, at 10, 15, or 20 minutes each for a total of 30, 45, or 60 minutes for the heavily aerobically inclined. An example might look like elliptical-rower-bike or any other combination. 

Another option could feature Low Intensity Interval Training using alternating short bouts on the treadmill, stairmaster, or air bike with a calisthenics circuit. This is very similar to many HIT or high intensity interval training workouts, but you can turn it into a Zone 2 experience by simply backing off the effort a bit. 

Wow…that was fun. We only talked about one type of training and we didn’t necessarily hit every little nuance. I hope you got a few pieces of actionable information from this and thank you so much for joining me today.