There has been a lot of noise in the cycling media about training at 'Zone 2'. Inspired by a question from one of my riders (thank you Rich) I thought I'd have a dig around to find out what all the fuss was about. This is what I discovered.

​Take away messages
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• The 'new' Zone 2 definition best equates to 70 - 80% of max heart rate or approximately 75 – 85% of FTP
• Zone 2 power is less intense than Zone 2 heart rate. The distinction between power and heart rate measurement is important because they do not equate 
• Rides of 60 mins to 2 hours in Zone 2 measured by heart rate, power or breathing should you wish to try that approach, remains an effective way to build aerobic endurance 
• The 80/20 principal is tried, tested and effective in terms of training load
• Zone 2 does not train the body to use fat as an alternative fuel source to carbohydrate and fasted training is a waste of time
• Zone 2 training is not new. The principles are tried and tested and it’s proved to be effective in developing fitness when augmented with high intensity efforts

Introduction

It makes sense to trust the training methods we know work, so novel approaches or new framings of existing training protocols should be welcomed but examined with a critical eye. Accordingly we should be rightly cautious about claims of efficacy of the latest training fad or the promise of quick fixes if they’re being sold without good evidence. Recently there has been a repackaging of ‘Zone 2’ training as all that is needed for race winning fitness. With training advice awash with ‘bro science’ this is, as you might expect, bollocks.

Tadej Pogačar’s coach, Iñigo San Millán’s message about the importance of Zone 2 training has been widely misinterpreted and misapplied. Whilst it is tempting to believe race winning performance emerges from a few hours of relatively easy riding measured by conversational breathing, it does not. However, Zone 2 is a vital component of a training mix to develop fitness but the nuance of the message has been lost. This piece will therefore address
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• Why the big fuss right now about Zone 2?
• How Zone 2 is defined in terms of intensity & what this means for duration and frequency
• What training in Zone 2 does and, importantly, does not do
• How it can be effectively implemented and measured

​Why the big fuss about Zone 2?
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Most of those involved in endurance training understand the value of longer endurance rides at relatively moderate intensities. Amassing base miles as part of periodised training over the colder months as preparation for cycling or racing in the warmer ones is not new so why the fuss now?
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• The celebrity of Iñigo San Millán, coach to Tadej Pogačar and other riders in the top 20 world rankings who is credited with the current hype around Zone 2. Cycling content creators have jumped on this and produced the usual ‘this is what you should do this week’ stuff
• A genuine counterpoint to the lack of performance gains from the Zwift generation characterised by short, hard training sessions and virtual races.  
• A questioning of whether the data produced by wearable technology is actually useful. Heart rate and power measurement is now ubiquitous but recently use of CGMs, HRV, sleep monitors and AI coaches has increased. The ‘Zone 2 by breathing’ message harks back to simpler days.   
• It sounds like an easy fix. By the time the advice has been filtered by the content creators and social media, the message is one of high performance without the hard graft of interval training.

​Defining Zone 2 – Intensity

How Zone 2 is defined depends on what is used to measure it.

The ‘San Millán’ definition of Zone 2

When interviewed San Millán defines Zone 2 intensity with reference to breathing, training whilst being able to hold a conversation or breathing through the nose. This is a very broad ‘measurement’ open to interpretation depending, amongst other things, on the nature of the conversation and the size of the nose. However, San Millán agreed with a question put to him by Dr Peter Attia that 70-80% Max heart rate is probably about right.

Zone 2 power

Andy Coggan (in Training and Racing with a Power Meter) who developed power zones based on a measure of Functional Threshold Power, defines Zone 2 as 56 – 75% of FTP. Joe Friel (in The Power Meter Handbook) says the same. Interestingly, Training Peaks rounds this up to 60-80% of FTP which, at the top end makes quite a difference, and Zwift in their Blue Zone 2, call it 60-75% of FTP.  

Level 2 heart rate

Peter Keen who worked with British Cycling and Chris Boardman in the 1990s who pioneered heart rate and power measurement for cyclists defines Level 2 heart rate as 70-80% of max HR. This aligns with Dr Stephen Seiler’s Green Zone training which suggests an intensity not exceeding 80% of max heart rate.

Lactate threshold

There are 28 different definitions of lactate threshold and it’s not something that can be routinely monitored outside of the lab although, as you can imagine, a ‘wearable’ is being developed. For our purposes, the body will clear the lactate it generates at an intensity below 80% of max HR.  Fundamentally, this is steady state riding and, for our purposes Zone 2.
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In summary, in my mind at least, San Millán’s breathing/metabolic measured approach translates better to heart rate (an effort metric) than power (an output metric) and his Zone 2 does seem to equate broadly to 70-80% of max HR. The distinction between power and heart rate measurement is important because they do not equate. Zone 2 power is less intense than Level 2 heart rate. 

Defining Zone 2 – Duration

Using power as a metric, it’s unlikely you’ll find cycling coaching advice that recommends more than 6 hours at the bottom end of the zone 2 in one single session or more than 4 hours at the top. The possible exception being Ironman distance related. Boardman reckoned he would spend no more than 2 hours at an intensity of 70-80% of max HR at any point. However, all training is on a curve and the lower the intensity, the greater the potential duration and vice versa. San Millan talks about rides of 90mins or so in duration being effective which indicates to me Zone 2 based on power measurement is likely to be too easy to match his definition.

For practical purposes, rides of less than an hour are likely to be too short, more than 4 hours and it’ll drift into Zone 1. It seems to me durations of 60 mins to 2 hours in Zone 2 measured by heart rate,  breathing (should you wish to try that approach) or power at 70-85% of FTP is an effective time frame.

Defining Zone 2 – Frequency  

San Millán talks about riding at his Zone 2 for between 2 to 4 days a week. 2 days a week in the cycling season (on the assumption racing or events are happening) and 4 days a week during the training phases of the year.  This is a repackage of the 80/20 rule. A 5 hour training week would break down to 4 hours Zone 2 and 1 hour at higher intensities. The intense hour may itself break down to 80% Zone 2 (warm up, cool down and rest periods) with 20% at Zone 5 during interval training.
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This makes sense but is nothing new. The 80/20 principal is tried, tested and effective. Most balanced training programs allowing time for recovery and ‘real life’ will broadly fit into this healthy mix. 

What Zone 2 training does, and doesn’t do

At its core it’s bike riding and is essential for all those adaptions, muscular, metabolic, cardiovascular, technical, tactical and psychological on which high performance is based. It’s base miles and you can’t build high performance race winning intensity without it. However, there are some misleading claims about what it else Zone 2 does.

1. It trains the body to burn fat as an alternative energy source. Sadly not. The claim is the body is being trained to use fat, as opposed to glycogen, as a fuel to spare glycogen stores for later use. However, it has been demonstrated that any type of aerobic training, including HIIT, increases fat oxidization at a similar rate.
2. It helps as part of ‘fasted training’. It doesn’t. Fasted training is an uncomfortable waste of time. Carbohydrate is an essential fuel for endurance training and is readily available even on the move. Training without it on a regular basis is ineffective and potentially dangerous.  It’s ‘bro science’ at its worst.
3. Fat burning for weight loss. No, again it doesn’t work partly because exercise in general doesn’t support weight loss but also because more fat is burned as higher intensities only the proportion of fat to glycogen changes.
4. It generates high performance. Not really, at least not in isolation. It’s an essential component but it needs to be supplemented with a mix of high intensity training or one becomes adapted to Zone 2 and nothing more.   

How Zone 2 training is implemented and measured 

When asked ‘how much should I do?’ San Millan is cautious, with good reason, about being too specific on intensity, duration and frequency. Of course, each athlete is different so maybe it’s an impossible question, but it also maintains an air of mystery. Bringing together what I’ve heard him say about intensity, duration and frequency, it boils down to 2 to 4 days per week at 90 mins per session with conversational breathing as a measure of intensity. In fairness to him, I think this is about as close as you can get to saying something helpful and it's more informative than 'it depends on the individual'. However, it raises as many questions as it answers about how precisely it should be applied.

Conclusion

For what it’s worth, I think San Millán’s Zone 2 definition equates broadly to 70 - 80% max HR. This is a really effective training zone and, however measured, we definitely need a proportion of it and 80/20 is not a bad starting point for mapping frequency and duration. Precisely how much, when and how often is going to depend on the goals and physiology of the individual rider. 

Whilst it might sound like pedantry, the subtle differences are important to get the benefits of training at Zone 2. Undercut it and it’s ‘junk miles’, overdo it and it risks over training and fatigue. Heart rate and power zones don’t match well but, using power as the measure, I think it equates better to 70-85% rather than the standard parameters of 56 to 75% of FTP. This is over the mid-point of Zone 2 power potentially merging into sweetspot (88% FTP) for a duration for 60mins. For rides up to 2 hours in duration 70% of FTP feels about right. Heart rate and power measurement used in tandem provide powerful metrics so try it and see? Do a 20 minute warm up and an hour at 70-80% max heart rate and see what Normalised Power is produced. Also, see how it feels and be conscious of your breathing - it's not easy riding. 

If you’ve fought your way through all this (well done and thanks) and have come to a big ‘so what?’ that’s pretty much where I got to too. To get fitter, doing a proportion of training at Zone 2 is great advice but it’s nothing new. That it needs to be programmed carefully and sustainably in combination with more intense work should come as no surprise either.
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Good old Zone 2 has just had a glow up, it’s been framed with a little mystery and accelerated with a sprinkling of celebrity stardust. The risk is that it is misinterpreted as it’s all that’s needed to generate high performance. I don’t think Tadej Pogačar is getting race fit with 6 hours a week riding whilst chatting and his coach does not make this claim. However, the power of his message and its attachment to Pogačar has become amplified by celebrity and distorted by influencers.

A casual flick through social or main stream media will leave the reader in no doubt the prevalence of mental illness is on the rise in the UK. It’s hard to avoid news and commentary programs on television that don’t frame stress and anxiety as part of the ‘permacrisis’ that seems to be integral part of everyday life. Indeed, a survey carried out by the NHS in 2014 revealed 1 in 6 people in the UK are experiencing a common mental health disorder, most commonly anxiety or depression. Now, NHS figures show this has risen to 1 in 4. 

The figures are alarming. Ironically stressful and depressing in fact, but they do require a certain amount of unpacking before they can be unquestioningly added to fuel the bonfire of worry engulfing the UK. In particular, questions about how anxiety is defined, about how it is experienced and about how it is treated both by health care professionals and addressed at a policy level by government should be addressed.  
 
The Oxford Dictionary of Psychology defines anxiety as a feeling of dysphoria (unease and dissatisfaction) together with symptoms of tension such as elevated heart rate, a tightening in the stomach and a dry mouth. This is a useful start, but it does little to explain the emotional impact and crippling dysfunction this can have on individuals and how it can make everyday life an insurmountable challenge for some.

 
How anxiety is experienced in the real world, and why it is a problem unique to humans is helpfully illuminated by Mark Williams, a Professor of Clinical Psychology at Oxford University. He asked an audience to imagine a scene from a wildlife documentary where a lion was circling a herd of gloriously oblivious impala. Gazing calmly, seemingly without a care in the world, when the impala become aware of the lion’s presence, they stop grazing and look up to locate the danger. As the lion charges, their natural ‘fight or flight’ instinct kicks in. Eyes widen, heart rate increases, muscles tense and the impala run flat out to escape unenviable prospect of being lion lunch. However, whether the lion is successful or not, it is only a matter of minutes before the impala resume their calm grazing. Seemingly oblivious to the recent attack and unconcerned about its inevitable reoccurrence.

​​Thankfully, most humans don’t have to deal with lion attacks but they do have to deal with attacks of different kinds all the time and, unlike the impala, have evolved a mind that is capable of remembering past traumas, projecting future ones and conjuring up the prospect of imagined ones, however fanciful, and adding them all to a complex social world. It seems humans don’t have the luxury of returning untroubled to peaceful grazing.  
  
This raises the question of whether anxiety, however unwelcome, is a natural and necessary state, an essential survival mechanism and something that should be accepted and managed as part of being human.

For those dealing with intrusive anxiety, a visit to the GP is often the first, and entirely sensible, point of call. Perhaps unsurprisingly, a doctor is likely to frame this as a pathological problem – an illness that needs to be treated and will respond by either.
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• Prescribing medication –The drug most commonly prescribed for anxiety is an antidepressant. The guidance used by doctors for diagnosing mental illnesses via symptoms described by patients, DSM5 now has 12 competing definitions for various types of anxiety and contains a list of symptoms open to interpretation. Psychoactive drugs alter brain chemistry to suppress symptoms rather than address causes and whilst they can be effective, challenges have been raised about their long term efficacy. 

 

• Recommending a talking therapy - Most commonly a type of Cognitive Behavioural Therapy (CBT). This aims to investigate the underlying thinking and feelings generated by anxiety and take practical steps to address any resulting unhelpful behaviours. Talking therapies for anxiety have been shown to be effective. However, questions have been raised about whether short course psychotherapy is really focused on making people economically productive by returning them to work rather than dealing with underlying problems

Importantly, the prescription of drugs, psychological therapy, or a combination of both, treat anxiety as a problem or deficiency centred in the individual. This frames the experience as a personal failing of biology or cognition and, by extension, something that is the responsibility of the individual to address, albeit with help.  

However, there is a growing recognition that humans are social animals and, unlike impala, live in a very complex social world. A study in evolutionary psychology indicated, when compared to other primates, a disproportionately large part of the brain has evolved to deal with negotiating our social structure, thinking about others, what others might think, what others might think about us and even what others might think about others. It’s perhaps unsurprising that, although our minds are adept at dealing with the social affairs of those we are intimate with, when faced with multiple social triggers, often delivered with urgency implicated in the bleeps and flashing lights by a treasured hand held device, we struggle to cope. We live in a world where it seems everything is after our immediate attention.

There is a body of evidence suggesting that poor mental health generally, and anxiety specifically, is influenced less by biology or cognition and far more by our social circumstances. Particularly relevant in a post Covid, cost of living crisis dominated world, studies have shown inequality, characterised by a growing gap between the ‘haves’ and the ‘have nots’, together with increasing individualism and materialism have significant negative impact on a sense of well-being and a healthy mental state.

The medicalisation of anxiety (and depression) also sidesteps a growing body of evidence showing that training and physical exercise is effective in relieving the intrusive symptoms of both. Simply, a daily 30 min walk outside can help but weight training and cardiovascular training is even better. However, drug companies don't make money by telling people to go for a walk. 

Arguably, against a background of the breakdown of the family and the erosion of trust in institutions, it is reasonable to question whether anxiety really is a problem that can be solved by medics, drugs and therapy or whether changes in public policy would be more effective. Whilst medical professionals should be the first port of call for those struggling with serious mental health problems, including anxiety at a debilitating level, it is inexcusable to ignore the evidence of a strong societal influence and the positive benefits of reconnecting with our environment through exercise. 

Rather than drugs and therapy, perhaps a more equal and accepting social landscape coupled with a daily walk would be more likely to support our return to peaceful grazing.