Triathlon training in Zone 2 is “trendy” at the moment, although it’s nothing new. Phil Maffetone pioneered his MAF training back in the 80s which focused on lots of training at low intensity, moderating an athlete’s effort by using a heart rate monitor. But what is zone 2, and how can it benefit our triathlon performance?
Before we get too far into the weeds, I wanted to take you on a whistlestop tour of the body’s aerobic system, and how it is critical to triathlon performance.
All human movements requires adenosine triphosphate, or ATP. ATP can be created with or without oxygen. If we are creating ATP in the presence of oxygen we are using our aerobic system, if we are creating ATP without oxygen, we are using our anaerobic system. The bad news here is that our anaerobic system can only sustain us for around 90 seconds on its own. It is designed for fight or flight situations, for us to outrun a sabre tooth tiger or lift an incredibly heavy weight. As triathlons last longer than 90 seconds, we’re going to need some oxygen.
I probably don’t need to tell you that we use our lungs to inhale oxygen. When oxygen reaches our lungs, it makes its way through tiny air sacs in our lungs known as alveoli. From here it passes into our bloodstream, and hitches a ride on our red blood cells, which transport the cells to our muscles, where it is converted into ATP, and used to contract muscles, providing movement.
Imagine someone heading out of their front door on January the 1st for a run to lose weight. They lace up their shoes, turn left out of their door and start their first run. Before they even reach the end of their road they’re doubled over and gasping for air, walking back home embarrassed and demotivated.
There are two problems here. The first is their very underdeveloped aerobic system. In their sedentary state, they have very small, inefficient lungs, and a small, weak heart. The result of this is that we don’t get a huge amount of oxygen into our bloodstream. When the oxygen does make its way into our bloodstream, our heart has to work really hard to get it to our muscles to create movement.
The runner in questions perceives this as a sense of breathlessness, as well as their heart pounding in their chest. Their body is screaming out for more oxygen to be able to continue the run at the current intensity, which brings me onto our next problem.
The intensity of the run was too high for their current fitness. Their experience of running may have been from playing team sports when they were younger, and they associate running with sprinting. However, they need to run at a much slower pace to be able to continue for a prolonged period. If you ran a half marathon with a friend and they started with a sprint, you’d tell them to slow down and pace themselves, the same principle applies here.
Our new runner probably needed to run for a minute, then walk for a minute, repeating this five or six times for his first run. However, suggest this to a lot of runners and they’d baulk. They want to run, not run and walk. This is part of the instant gratification mindset a lot of us have developed in recent years. We want everything right now, and we want to enjoy it. If we don’t love every minute, we’ll find something else to do.
I know this is all a bit technical, but it’s important to understand what’s going on in the human body to appreciate the benefit of zone 2. I neither want to overwhelm you with information or patronise you.
It’s a common belief that the body switches between aerobic and anaerobic systems like a light switch, but the difference is a lot more nuanced. You are getting an extremely low level of energy from your anaerobic system while reading this, ticking away like a pilot light, ready to jump into action at a moment’s notice if that sabre tooth tiger appears.
When we train in zone 2, our body is probably getting 99.9% of its energy from our aerobic system, which means that we’re getting maximum training benefit from our aerobic system. As we start to move into zone 3, our body uses significantly more of our anaerobic system, in zone 4 we use a lot, and in zone 5 (or above) we may be almost entirely reliant on our anaerobic system. This compromises the training benefit we gain for our aerobic system (in most cases), and also causes a lot of fatigue.
The result of training at this higher intensity is less aerobic development and more fatigue generated. Am I saying we never want to train in any other zones? Absolutely not, there are benefits to every kind of intensity out there. Even the zone 3 we generally try to avoid is great for developing muscular endurance and half marathon pace. Let’s dive into why we may want to train in zone 2 for two different types of athlete
If you are training for a 70.3 you are probably looking at around five or six hours of racing in most cases, maybe up to seventeen hours if you are taking on an Ironman. This is a really, really long time to be moving forwards.
Sticking with the Ironman example, if you were to head out for a seventeen hour run, how fast would you set out? Chances are you would head out in zone 1, maybe zone 2. So when taking on an Ironman triathlon, which zone will we end up racing in? Hopefully, we’ll be able to hold zone 2 throughout. In fact, zone 2 is probably our best case scenario. When you consider how many Ironman athletes push their bikes up hills and walk big chunks of the marathon, if you offered most Ironman finishers the chance to have got round in a steady zone 2, most of them will have bitten your arm off.
You may be enchanted by images of professional athlete crushing 2:45 marathons and feel that’s what a successful Ironman athlete looks like. To emulate that kind of athleticism, you need to get faster, and you get faster by running fast, right? Well, yes, anyone following my training plans will be doing lots of hard intervals, but we also need to build up our time in zone 2.
The secret of the pros that helps them knock out a 2:45 marathon split at the end of an Ironman? Swimming in zone 2, cycling in zone 2, and running in zone 2. Yes, some pros can run at 4:00 per KM and still be in zone 2. How can they achieve that? Tens of thousands of hours of consistent training over several years in the sport, primarily in zone 2. Most professional Ironman athletes at the front of the field have been in the sport for 10+ years, and from years spent doing zone 2 training, they can hold high a high power/pace while keeping their heart rate low. There’s no shortcuts to this, it just takes a LOT of time and work, much more than your average age group athlete can dedicate. So I’m afraid that your chances of running a 2:45 Ironman marathon are limited!
For the short course athlete, zone 2 can be a harder sell. Where most Ironman and Ironman 70.3 athletes will be racing in zone 2 (or maybe low zone 3 in the case of a 70.3), for a sprint athlete it can be frustrating to have to run at such a slow pace. Why aren’t we doing threshold intervals or hill sprints?
The answer is that the sprint distance is still heavily dominated by the aerobic system. There may be time spent anaerobic, especially on the bike in a draft legal race, but the biggest limiter for most (thought no all) athletes will be their aerobic system. Lungs burning on the 5KM run? Getting out of breath on the hills? These will all be improved by superior aerobic fitness.
This may surprise you, but even team pursuit riders do most of their training in zone 2. For those unaware, the team pursuit is a cycling event which takes place on the track, with most events lasting around four minutes. So why are they spending so much time training in zone 2? Because even at four minutes, we are reliant on our aerobic system to produce most of our energy. And the best way to improve the aerobic system? Time in zone 2.
As with most endurance sports, triathlon is a bit of an arms race. Not to see who can buy the fastest, lightest bike, but who has the most time available for training. An athlete who trains for 20 hours a week is going to be faster in nearly every situation than an athlete who only trains five hours a week. However, to gain an advantage here, our 20 hours needs to be the right kind of training. How many Zwift races, sprint sessions and 5K races can you fit into a week without exhaustion? For someone training 20 hours a week, I would normally expect them to fit in three, maybe four high intensity sessions a week. Any more and our recovery between the sessions will be compromised, affecting our adaptation to the stimulus. You can do all the hill reps in the world, but if your body is in a constant state of exhaustion, you won’t actually get any fitter.
The Brownlee brothers, the most successful athletes over short course the world has ever seen, still did 100 mile rides and runs that far exceeded 10KM. They also did a lot of brutal training sessions, which helped them achieve their success, but it was all underpinned by an enormous foundation of aerobic fitness. Aerobic fitness primarily developed by time in zone 2.
Popularised by exercise physiologist Stephen Seiler, this method of training revolves around 80% of training sessions being primarily zone 2 based, and only 20% of sessions being above this. A common misconception is that 80% of your time should be in zone 2 and 20% in zones above this, but it is in fact a reference to the number of sessions. Taking into account the warm up, cool down and rest periods of an interval session, we may only actually spend 10% of training time above zone 2.
Honestly, I don’t agree with the 80/20 rule. I think that it’s too restrictive. It also stipulates that of the 20% of interval sessions, most of them should be spent at VO2 max, which is a very high intensity we will touch on in more detail later. The absence of any meaningful time spend at tempo or threshold is an issue for me. We need aerobic fitness by the spade, but we do need to develop our muscular endurance as well. Zone 2 will do little to challenge your muscular endurance outside of very long sessions, so we need to include intervals longer than three minutes in our training.
In fact, while almost every sports scientist and coach out there advocates 80% of your training being in and around zone 2, what we can’t quite agree on is what to do with the other 20%. What the ideal mix of VO2 max, tempo, threshold and sprints is. I don’t have a strong opinion here, as I really believe it comes down to the athlete, their goals and their limiters.
Many age group athletes eschew the idea of a polarised approach like this, but most professional Ironman athletes follow a split closer to 90/10. Even if as a sprint athlete you moved closer to 70/30, you’re still going to see improvements in your times.
I have made a few references to this so far, so wanted to clear this up for those who are unaware. VO2 max is a measure of how much oxygen your body can process, and is measured in millilitres of oxygen per kilogram of bodyweight (mL/kg/min). Generally speaking an athlete with a higher VO2 max will be faster than someone with a low VO2 max over longer events, but this is not a direct correlation, as some of the world’s greatest athletes have fairly low VO2 max values relative to their competition.
The bad news is that VO2 max is genetic to a large extent. It can be trained, but you will hit a glass ceiling. The two most effective ways to train your aerobic system are though zone 2 training, and VO2 max training.
VO2 max is also used to refer to an intensity where we are training at the maximum intensity we can without our anaerobic system taking over. Intervals at this intensity are generally around 1-3 minutes, maybe 4 at a stretch. When you are riding at VO2 max you are stimulating development of your aerobic system by placing your lungs and heart under the absolute maximum strain possible, which is going to be unpleasant, but at least it will be over quite quickly! For these intervals, your rest period should be equal to that of the interval, so if you are riding two minute intervals, you need two minutes of rest between each interval at allow the body to recover.
Broadly speaking, I like to include one VO2 max workout a week with most of my athletes, in either swimming, cycling or running. Some coaches like to include two sessions, but I feel this is a bit excessive, and athletes appreciate more variety than simply rotating between zone 2 and VO2 max.
I’m sure a lot of you will be struggling with this concept. “You mean I have to ride/run really slowly? But that’s easy, and I want to get a REAL workout in”
It’s true that a zone 2 workout won’t leave you feeling as battered at other training, but that’s half of the beauty of it, it allows you to recover from your harder sessions, so you’re ready for your next interval session, while also providing the optimal fitness benefits for the time spent training. We need to disassociate ourselves from a correlation between how exhausted we feel and how effective our training is.
There is also the concept of someone feeling embarrassed when out training in zone 2. I’ve lost count of the amount of times I’ve wanted to reach through my keyboard and give athletes a slap for pushing way above the target intensity in a workout because they didn’t want to get overtaken, especially on virtual platforms. This to me is a symptom of a fragile ego, and of someone not confident in themselves and their ability. When I’m out riding in zone 2, I get overtaken by women, juniors, old men, and everyone in-between. They wish me a good morning, I greet them positively, and keep riding. Why don’t I let it get to me? Because I know I could probably crush most of them in a ten mile time trial if I needed to, but that’s not the aim of today’s workout, the aim of today’s workout is to get some good miles in without a tonne of fatigue.
Then there is the boredom aspect that many report struggling with. Many just starting out on their running journey will run fast in most of their workouts, with music pounding in their ears to keep them going, and finish each run feeling wiped out. They want a workout, to burn calories and get fit. Running is an intensive experience for them. For most really fast runners, it’s actually more of a mediative experience in most cases.
Using myself as an example here (sub 18 5K runner), I can trot along in zone 2 quite happily while either listening to an audiobook, podcast, or just taking in the sounds of nature on a rural run. When I first started running I struggled not to run to music, but over time I learned instead to listen to my body. The key to reaching this state of calm and confidence? Plenty of longer runs.
Nearly every training programme will have you running at zone 2 in your long runs, and what will feel easy during the first hour is going to really start to bite by the end. Could you hold that pace for 42.2KM and still feel fresh afterwards? If the answer is anything except a firm “yes”, then the intensity is correct. Running at 5:40 per KM may feel slow, but it would give you a sub 4 marathon finish, putting you in the top 50% of finishers. Does this sound good? Then stick with the training.
Still struggling with the thought of this? Find somewhere new to run, mix up your routes to keep your brain engaged and help things feel new. Maybe even get in the car and drive somewhere new to keep yourself stimulated.
I appreciate it can be difficult to motivate yourself to stick with the training, but look at it this way. What is easier to change? Your mindset, or the laws of science? Obviously, I can’t stop you or anyone else from going out and doing all your runs fast, and you’ll no doubt feel great for the first half of your event, but if you find yourself walking most of the last 10KM, being passed by people you would crush in a 5K, you can make all the excuses you want, but the most likely reason for you failing to achieve your goals is that you let your ego and frustration dictate your training.
Hopefully by this point you will have recognised the need to train in zone 2 if you’re serious about improving as an endurance athlete. You have recognised that this isn’t just a fad, but how elite athletes have been training for decades, which is finally filtering through to amateur athletes. However, we need to look at the logistical side of things, or how we train in zone 2.
At this point, I could do one of two things. I could give you a long list of calculations to do, or I could keep it simple and refer you to external sources.
I highly recommend you open a free account at Trainingpeaks.com, which will help you manage your thresholds, by emailing you whenever it believes you have set a new threshold. When you setup an account it will ask for your thresholds, which can be calculated using the following methods: https://help.trainingpeaks.com/hc/en-us/articles/204071934-How-to-Calculate-Threshold-Power-Heart-Rate-or-Pace
To confuse matters even more, there are three different kinds of zone 2. Heart rate zone 2, pace zone 2, and power zone 2. So, which one should we be using?
In many ways, heart rate is the true zone 2. It shows us what is really going on in our body, and how hard it is working. However, using heart rate zone 2 is not without issue. Heart rate monitors can be temperamental, and your heart rate will be elevated some days due to factors unrelated to your training, where you just can’t keep your heart rate in zone 2, causing immense frustration. This frustration will be magnified if you try to use the HRM built into your watch which isn’t accurate enough for training to. You NEED to invest in a chest strap if you plan on training to heart rate. Generally speaking, I recommend using other forms of metrics to measure which zone you’re training in.
Pace zone 2 for running requires a run threshold test, which is a 5K or 10K all out effort. This can be integrated into the plan as a fun C race to check if an athlete’s zones are up to date, or executed as part of a run around a park. If you are doing this in an uncontrolled environment, try to choose a route with minimal junctions, where you won’t have to give way to pedestrians or cars at any point. If you can choose a nice flat course as well that would be useful and give you a better idea of your time. Once you have your finish time, input it into TrainingPeaks (settings>zones> speed/pace), where it will calculate your zones for you, including your zone 2. When out running, instead of following your heart rate, you instead follow a pace target. The issue here is that if your watch doesn’t have a good lock on the satellites, such as in heavy woodland or on very cloudy days, it can be hard to track your intensity.
There is also swimming pace zone 2. I recommend someone completes a swimming CSS test, which takes the form of a 400M all out effort, followed by a 200M all out effort, putting the results into a calculator such as this one: https://www.swimsmooth.guru/login. From here, you will have your swim zones.
Finally, we have power zone 2, which is probably my favourite as it is very objective and responds instantly to changes in intensity. It requires a cycling power meter or smart trainer which does place a financial barrier to this training method, although these have come down in price in recent years. I won’t go into the weeds of FTP testing here, but if you are a newer cyclist I generally recommend the ramp test (with ERG mode engaged) rather than the 20 minute test.
Far from it, just because we’re not necessarily training TO heart rate doesn’t mean we shouldn’t be tracking it. It gives us a great window into what’s happening in an athlete’s body. If someone is running in pace zone 2 and their heart rate is in zone 2, we know all is well and their training is going to plan. Thumbs up all round, let’s keep up the good work.
If they’re running in pace zone 2 but heart rate zone 1 for most of. the session, their pace zones are too low, and they probably need to be running faster. At this point I will schedule a pace threshold test when appropriate to test for improvements.
What if they are in pace zone 2, but heart rate zone 3? Well, this tells me they are likely fatigued, unwell or otherwise out of sorts. If they are consistently in heart rate zone 3 on all their runs, I have two options, I can lower their target pace, or wait for their fitness to improve to the point their heart rate will drop. Every single time I will opt for the second option, it’s very demotivating to lower someone’s threshold, especially based on heart rate data which can be inaccurate. If they feel good and strong at that pace, are able to complete their long runs and feel ok, we should probably leave it as it is, as their heart rate will drop to zone 2 for that effort over the coming weeks and months. This is especially common for athletes who test very well, and can really dig themselves a huge hole in their fitness tests, but may not have a great aerobic base.
It is worth highlighting at this point that you should probably set different heart rate zones for running, cycling and swimming. Running will always have the highest heart rate for a given effort as it uses just about every muscle in the body, followed by cycling, and then swimming as the horizontal nature of the activity makes the heart a lot more efficient than being vertical. There is functionality for this in TrainingPeaks, as well as different calculations for both running and cycling.
Despite what some would have you believe, slipping briefly into zone 3 on a hill does not ruin your session. Our zones are never 100% accurate, and there is a definite overlap between zones. High zone 1 isn’t all that different to low zone 2, and high zone 2 is similar to low zone 3.
For this reason, I recommend athletes stay to the bottom of zone 2, as you are getting the benefits of the session while generating minimal fatigue, helping you crush your next interval session. You can butt up right agains the top of zone 2 if you want, but this is more likely to be driven by ego than good training principles.
This is a common complaint about zone 2 training, and one that I empathise with. For newer runners, as soon as they start running their heart rate hits zone 4. They then complete a pace threshold test to get a pace zone 2 to run at, but this comes out at a pace it is simply impossible to run at without borderline bouncing up and down on the spot. While I don’t mind running slowly, I certainly don’t want to be awkwardly lolloping along at 8:30 per KM in full running kit.
If your zone 2 is more of a fast walk, then going out for a long, fast walk is my recommendation. You probably want to do this in trainers, but not your full running getup. Keep doing this for a few weeks, and you’ll start to see improvements in your running time, and you should be able to set a new pace threshold. People often overlook walking, but it’s a great fitness tool, and provides a multitude of benefits, especially for novice runners.
There can also be issue with cycling, where you are travelling so slowly on your bike outdoors that you don’t feel safe, or swimming so slowly in the pool that you start to sink. In these situations, it’s a good idea to fall back on the talking test. If you can hold a full conversation while swimming, cycling or running at that pace, then you’re probably in the right ballpark. I don’t recommend trying to talk while underwater, but if you could finish a length and immediately speak in full sentences, that’s a good sign. As I mentioned above, the zones all meld into each other a bit, rather than being binary.
Look, you’re a grown adult and I can’t force you to do anything, only advise you, however as part of my closing argument I want you to consider the bigger picture.
Doing all of your runs above your race pace will make you very good at running above your race pace. If you’re training for your first Ironman or Ironman 70.3, your race pace will probably end up being slower than you realise. Finishing every workout drenched in sweat and with sore legs may feel great in the moment, but it’s not going to do much to help you during an Ironman or Ironman 70.3 run. I could win 5K races ahead of my first Ironman, but that didn’t stop me putting in a 5:30 marathon during my first full distance race due to a lack of appropriate training. I was working seven days a week ahead of the event, so just couldn’t get the volume in that I needed.
As I alluded to at the start of the article, we have become a society used to quick fixes of serotonin and instant rewards. We have become hooked on taking Strava KOMs, trying to keep a high average speed to impress other people, or focusing simply on short term happiness.
Those athletes who can’t think beyond how they feel in there here and now are the equivalent of someone who inherits some money, and uses it to put down a deposit on a car they can’t afford at a 27% interest rate, while the athlete who spends their time doing a very un glamorous 90 minute run in zone 2 run is the equivalent of someone who puts an inheritance into savings and safe investments. There will be repercussions on choices we make for a quick hit, whether it’s the repo man coming to tow your dream car away, or walking the run of your Ironman.
I hope you have found this article to be interesting and now understand the why of these boring sessions. While I do what I can to keep training sessions varied by manipulating cadence and intensity targets within a session, sometimes we need to choose to see these sessions as a chance to detox from our world of information onslaught, and switch off to just enjoy being outside.
Dozens of my clients have found this a difficult concept, but put faith in me and reaped the rewards on race day where they found they could just keep going relentlessly, vastly outperforming their expectaions rather than blowing a gasket and limping home.