The popularity of the term “Zone 2 Training” seems to have increased in recent years, not only within the field of endurance sports where you might expect it, but also within the context of field sports and general health advice.
Zone 2 training generally refers to continuous exercise (e.g. running, cycling, stationary cardio machine training) done at a conversational pace for a sustained period of time.
More specifically, Zone 2 refers to the second in a 5-zone heart rate based framework, where Zone 1 generally refers to a brisk walk or really slow jog, and Zone 5 refers to an all-out sprint.
Zone 2 here refers to a pace just above a jog, where you could still hold a full conversation, generally referring to somewhere in the range of 60-75% (as a very rough guide) of your maximum heart rate.
This is in contrast to what people often do when they “go for a run” - that is, run at a fast pace for as long as possible, feeling out of breath with burning leg muscles throughout.
In reality, this is probably closer to Zone 3 or 4 for most people.
Before getting into the specifics of Zone 2 training and whether it is in fact as important as its recent popularity may imply, I’m going to get into the topic of aerobic fitness, one of the main proposed reasons for including Zone 2 Training.
From there, we can look at the specifics of Zone 2’s role in developing that.
What is Aerobic fitness?
As obvious as it sounds, every activity we carry out, athletic activities included, requires the body to produce energy.
It produces this energy using 3 main systems in the body.
The first is known as the phosphocreatine system, which produces energy rapidly, when we jump, sprint, or throw, for example.
The trade-off for this system’s ability to produce energy rapidly is that it can only do so for a very short period of time, usually less than about 10 seconds, before it needs to rest and regenerate the substrates required.
You can imagine yourself trying to sprint at your max speed - you can’t hold it for very long before you end up slowing, and this is due to this system’s limitation.
The second system is the ANaerobic system (I’ve added capital letters to give clarity when discussing this and the next system).
This system also produces energy quickly (albeit not as quickly as the first) but can sustain it for slightly longer, potentially up to a few minutes.
However, it is limited by the fact that when it produces energy, it also creates a lot of byproducts (those correlated with increases in lactate) that contribute to fatigue.
It is also relatively inefficient in terms of the amount of energy it yields per gram of fuel (in this case, carbohydrates, or more specifically, glucose).
You can imagine yourself trying to run an all-out 1km time trial, and feeling the ‘burn’ in your leg muscles, correlated with a build-up of lactate - this is you finding the limits of your ANaerobic system.
NOTE: While lactate doesn’t directly cause fatigue (in fact, it can actually be recycled to be used as a fuel source), it is correlated with those byproducts that contribute to fatigue in the muscles, so for now, when I refer to increases in lactate, I’m also referring to increases in those byproducts.
The third energy system, the aerobic system, is slower to produce energy, but can do so for much longer periods.
In fact, this is the system that fuels the vast majority of our daily activities, as well as being the major contributor to any exercise or activity lasting longer than a few minutes.
It also is much more efficient with how much energy it is able to get from each gram of carbohydrates.
Furthermore, unlike the ANaerobic system, it can not only use carbohydrates to produce energy but can also use fats (or more specifically, fatty acids), meaning it has a practically unlimited source of fuel.
Why is it Important to Increase Aerobic Fitness?
The above description will likely make it easy to see why improving your aerobic fitness would be beneficial if you were running long distances, for example, and it is.
This is because the more well-developed a runner’s aerobic system is, the higher speeds and distances they can sustain before needing to either slow down, or significantly tap into their ANaerobic system.
But what you might not expect is that it’s also important for those engaging in activities that involve repeated outputs at those higher speeds that are more within the range of the phosphagen or ANaerobic systems.
For example, if you consider a field sport athlete like a GAA player or Rugby player, whilst the main sporting action happens at high speeds and intensities, most of an individual’s movement within game will be done at submaximal levels, which will be primarily fuelled by the aerobic system.
Not only that, but when the athlete is engaging in those higher-intensity, ‘ANaerobic’ runs, the aerobic system is responsible for the clearing and recycling of the lactate produced during them.
Finally, the ability of the aerobic system to use fatty acids for fuel can allow athletes to save their stored carbohydrates for when they’re needed in those higher intensity efforts.
What this means, both for runners and field sport athletes (as well as anyone else engaging in such activities) is that increasing aerobic fitness can lead to:
Increasing the speeds, intensities, and distances at which the aerobic system can be the major energy-producing system - that is, delaying the need for the contribution of the ANaerobic system and accompanying lactate build-up.
Increasing the ability of the aerobic system to clear and recycle the lactate produced by the higher-intensity ANaerobic runs - that is, better ability to sustain near-maximal runs for longer, and quicker recovery between them.
Increasing the overall availability of fuel (both at lower intensities and higher) due to the aerobic system’s ability to use fatty acids as fuel, and its efficiency when using carbohydrates.
The mechanisms through which these adaptations occur (including improvements in mitochondrial density, changes in their function, and increased heart stroke rate volume) are beyond the scope of this article, but might be discussed more in future articles.
“So Should I do Zone 2 Training?”
As you can imagine, Zone 2 training - again, low/moderate intensities sustained for longer time periods - predominantly uses the aerobic system.
For that reason, you might have made the obvious connection that Zone 2 training is a good way to increase aerobic fitness.
And you’d be correct.
However, what we haven’t touched on yet is that while these are distinct systems, they all overlap.
Meaning that even activities that require a large amount of ANaerobic system contribution will often also involve a large contribution from the aerobic system.
For example, a 1km max effort run will certainly require a lot of ANaerobic system involvement - you’ll know this from the burning sensation in your quads - but the aerobic system will still be heavily involved.
So that might lead you to the conclusion that the aerobic system can not only be developed by aerobic-focussed/low-intensity/Zone 2 training, but also by higher-intensity training.
And again, you’d be correct.
So you might then ask, do we need to bother with Zone 2 training?
Is there any benefit?
Is it an overblown fad?
Can’t I just keep running fast, pushing myself to my limits, getting out of breath, and engaging in my specific sports training?
Consideration 1: Training Load
Firstly, you can certainly increase aerobic fitness through higher-intensity training.
However, imagine you’re a team sport athlete, for example, who wants to further increase their aerobic fitness.
Imagine you’re already training hard 2-3 times a week with the team, playing a match at the weekend, getting in a couple of gym sessions, and managing the stress of day-to-day life.
The idea of adding in another high-intensity run or interval session on top of that without it taking away from the rest of your training might be unrealistic, both mentally and physically.
But, you might feel able to add in an extra 1-2 x 30-60 minute slow and steady stationary bike sessions, without it taking away from your ability to push yourself in team training and matches (when done with appropriate volumes and progression, of course).
Or take a distance runner aiming to get in 4-7 runs per week and accumulate 50-100 miles of volume.
Even the highest elites aren’t able to run all those at high intensities.
In fact, most elite runners will tend to run around 80% of their running volume at low intensities - Around Zone 2.
On the flip side, let’s say you’re someone whose current weekly training load consists of 3 gym sessions, and a few walks throughout the week.
As long as you’re starting low and building up over time, it could be a great idea to start adding in a couple of higher-intensity runs or interval sessions to bring up your aerobic fitness.
In fact, in this case, it will potentially do so better than the equivalent time spent doing Zone 2 training.
However, the key term there is “time”, where opting for Zone 2 training will allow you to take advantage of the decreased intensity by increasing how much time you can spend doing it, thereby increasing training volume, and increasing your aerobic adaptations as a result.
For example, most athletes could sustain a slow pace on the stationary bike for 60 minutes without a problem, but an hour of 400m intervals runs would be a completely different story, both during and after the session.
The key here is that any additional training should take into account your current training load and type, as well as how much time you are able to give to it.
If the additions place you beyond what you can recover from, both from a time and intensity perspective, it’s too much.
By decreasing the intensity (e.g. opting for Zone 2 training instead of higher-intensity training), we can potentially include more volume without having recovery be an issue, or at least as much of an issue.
Consideration 2: Sport-Specificity
In the examples above, the context is mainly that of adding training to your existing training load.
However, other factors need to be taken into account when creating a plan from scratch.
For example, all this talk of Zone 2 training and its advantages might have you wondering why you don’t just ONLY do Zone 2 training.
Well, there’s a good reason your football coach doesn’t have you just running slow laps around the field to develop aerobic fitness.
It’s because we have to consider the other adaptations that go along with the type of training we’re doing, rather than only focussing on aerobic fitness.
For example, you may be familiar with Tempo Runs, which generally involve running repeats at submaximal speeds for somewhere in the 10-30 second range, followed by 60-90 seconds rest.
Whilst these might not be optimal for developing aerobic fitness, they will likely improve it somewhat, whilst allowing athletes to accumulate some higher speed running, and getting the benefits associated with that.
This trade-off may be worth it in the scope of the overall development of the athlete if their sport needs them to run at high speeds repeatedly.
It may also be the case that too much time spent working on aerobic fitness might mean less time working on ANaerobic fitness and speed, and if these are important to peak performance in the sport, neglecting it would be detrimental.
As another example, even elite marathon runners don’t only run at Zone 2 pace.
This is (partly) because they also want the benefits associated with spending some time running faster: improving running form and economy, improving higher end aerobic capacity, improving their ANaerobic system, and other benefits.
The key here is that given that there are many intensities and methods of developing aerobic fitness, doing so in a way that matches the other demands of your sport may be necessary, especially given the time and recovery constraints.
“So, Again, Should I do Zone 2 training?”
If I was to put it briefly, if you’re someone who is hoping to improve your aerobic fitness further, is already doing sufficient sport-specific training, and has the time/recoverability to include some lower-intensity training without it taking away from other important elements of your training (or life), it could certainly be a solid option to start bringing into your overall training schedule.
This could be as simple as a 30-60 minute jog, swim, bike, or similar continuous activity.
For athletes who are already doing a lot of running in their sport training, opting for “off-feet” options for their Zone 2 training could be a good option to get the benefits without putting extra impact stress on the muscles and joints involved in running.
Of course, if their chosen sport is running, accumulating more time on your feet could be one of the advantages of including more Zone 2 training.
However, with all of the above said, whilst the Zone 2 training can be a great option to include in your overall training plan, neglecting other training methods that are more specific to your sport or athletic goals will be done at your peril.
Article Written By Conor O’Neill
You can find out more about The Everyday Athlete Program by going to everydayathleteprogram.com/coaching.