Zone 2 training has recently become a staple in my routine, and I can see why the experts are such keen advocates. Before now, I would force myself to go hard whenever I did a cardio or HIIT workout, but they never got any easier. If anything, they became harder. I’d go all-out on 5k runs and come back utterly exhausted, then try again a few days later, only to find it ten times harder than the first time around. Not enough rest days didn’t help, but zone 2 training has been just as instrumental in helping me recover and progress simultaneously. Here’s how.
What is zone 2 training?
Everything you do is powered by ADP (adenosine triphosphate) – the molecules in your body responsible for giving you energy, and everything you eat provides your body with the fuel needed to create ATP.
You create more ATP as you exercise, and which type of fuel your body uses is determined by which heart-rate zone you exercise in. Sports scientists have identified the following six heart rate zones and which energy sources they rely upon, with zone 1 being the lowest intensity (i.e. watching Netflix on the sofa), and zone 6 as the highest intensity (i.e. an all-out sprint):
Does zone 2 training burn fat?
Zone 2 training uses fat (and oxygen) as its energy source, as opposed to carbs, which is why it doesn’t feel as hard or uncomfortable as anything in zone 3 or above. Andy Vincent, a sports and conditioning coach defines zone 2 as: '65-75% of your max heart rate. It’s an “easy” run or cycle where you can maintain a conversation without getting too out of breath.’
What are the benefits of zone 2 training?
Though zone 2 training is physiologically easier than zone 3 and above, we hardly ever train cardio at such an intensity. Your spin classes, HIIT workouts and runs are almost definitely done above zone 2, while you’ll probably stick around in zone 1 for much of your strength training, yoga and Pilates sessions, too. The reason for this is that zone 2 doesn’t feel ‘hard enough’ for cardio or HIIT, but by not doing it, you could be missing out on some big benefits.
1.It improves your aerobic base
‘We have different energy systems in our bodies,’ Vincent explains. ‘At different intensities, your body uses different fuel sources. Think of this as a pyramid. The base of the pyramid is your aerobic energy system and is where zone 2 sits. This is where we use mainly oxygen and fat as a fuel source. The next level up (zone 3+) is the glycolytic energy system.
'If you improve your ability to exercise with a lowered heart rate (i.e. zone 2), without switching up to the glycolytic energy system by increasing your heart rate and going up a zone, you broaden your base. In turn, you improve your capacity to work at higher intensities with more ease as your cardiovascular system will be stronger.’
Laura Hoggins, an author and PT, adds: ‘Developing your aerobic base enables you to take on more training load, i.e. how often you train during a week and how intense your other workouts are, because you'll have a stronger aerobic capacity, meaning the harder workouts will feel easier.’
2. It increases your mitochondrial function and density
Vincent says: ‘Mitochondria are the powerhouse of your cells; they generate chemical energy for your body using oxygen. Zone 2 training increases the number of mitochondria you have and how efficiently they can work, as it stimulates the production of oxygen by using it (and fat) for fuel. On the other hand, when you start to surpass zone 2 and train harder, your body will start to use carbs to create ATP (i.e. fuel or energy) through glycolysis.’
Zone 2 training creates more mitochondria, and the more of this you have, the more ATP (energy) you can create through oxidation.
3. It improves substrate utilisation
‘This is a fancy expression that means your body can manage the use of fats and stored carbohydrates better,’ Vincent tells WH. ‘By working different energy systems in your body via a variety of heart rate zones in your training, your body becomes more able to switch between these fuel sources. This improves our efficiency at using energy and aids overall metabolic health.’
With zone 2 training, your body becomes more au fait with burning fat for energy as you use just fat and oxygen for fuel.
4. It lowers your resting heart rate
‘If you have a larger aerobic base, your body can manage higher intensities more easily, which materialises as a heart rate at rest and improved cardiovascular health,’ Vincent says.
5. It improves your recovery
‘With a larger aerobic capacity, you can supply your muscles with more oxygen both during and after exercise. You will also be more able to flush out lactic acid - the stuff that builds up in your muscles and causes DOMS - more efficiently. This means you can go again quicker and push successive bouts of training harder,' says Vincent.
Sure enough, one study showed that zone 2 training considerably increases oxygen uptake.
Hoggins often trains at high intensities and has reaped the rewards of recovery first-hand: ‘Zone 2 training has improved my ability to recover from any intense exercise I do,’ she says.
6. It improves insulin sensitivity
‘Due to the improved substrate utilisation mentioned above, your body gets better at shuttling glycogen (i.e. sugar) into your muscles for fuel. This improves your body's response to carbohydrates and regulates insulin production,’ says Vincent.
One study proved this to be true, showing that a 60-minute session in zone 2 can increase the insulin-dependent rate of glucose disposal by 67-97% in people without diabetes. In layman's terms, your body will become more able to dispose of glucose and maintain low blood sugar levels with a smaller amount of insulin.
Why is zone 2 training important?
‘It has been neglected over the last 5-10 years with the rise in popularity of HIIT, as . moderate forms of training have been seen to be less beneficial,’ Vincent explains. ‘But this is categorically not true. The better your zone 2 aerobic base, the harder you can push yourself when doing HIIT. The reality is, with a poor aerobic base, you aren’t getting close to maximising your higher intervals sessions (even if it feels like you're going all out), and your recovery will be impaired.
‘There has been a shift in focus towards longevity in training. Some of the most significant benefits of zone 2 training are the improvements to mitochondria function, and that it is less taxing on the joints and can help us destress.’
How to calculate heart-rate zone 2
Both Vincent and Hoggins offer two metrics to track: your heart-rate, and RPE (Rate of Perceived Exertion). Here’s how each works.
‘As a guide, somewhere between 60-70% of your max HR is what you should be aiming for,’ Hoggins tells us. ‘To find your max HR, try the following calculation:
‘But this shouldn’t be taken as gospel, as there are so many variables that can impact your HR and how your HR responds to different types of exercise,’ Hoggins caveats. ‘It also depends on how many muscle fibres are recruited in your workout and the level of impact.’
An example, for someone aged 30:
Max HR = (220-30) 190
60% of 190 = (60*190)/100 = 11400/100 = 114
60% of your max HR is 114bpm.
You’ll ideally have a fitness watch to track this number (Apple watches with OS 9+ will also display your heart-rate zones throughout your workout via the fitness app).
RPE stands for Rate of Perceived Exertion, and it’s a self-monitored scale of how hard you find a workout, from 1-10. Hoggins advises that zone 2 training would be around 3/10 on the RPE scale.
‘You can easily hold a conversation and maintain the same pace throughout your workout,’ she explains. ‘At zone 2, there shouldn’t be any lactate building in your blood, which is why you may well finish feeling more energised and brighter, as opposed to feeling totally whacked like you might with a HIIT session.’
Vincent adds: ‘The key to zone 2 is being able to maintain a conversation the whole time. You can set yourself a distance or timed targets to work with, but remember it’s a marathon, not a sprint. You should gradually increase the intensity of your sessions over time. Make sure you can breathe the entire way throughout the workout, and pay attention to your split times if you want to implement progressive overload over the weeks (i.e. how much stress you put on your body).’
Zone 2 training examples
To help you out, I asked Vincent and Hoggins for their tips on maintaining a stable zone 2 heart rate for the most popular cardio modalities. Here’s what they advise.
Vincent’s advice: ‘If you are not a good runner and even a jog makes you out of breath, then you need to choose a different form of cardio because you will struggle to maintain a lowered intensity. This could be a fast walk. Ideally, you want somewhere flat so there are no spikes in your heart rate and, where possible, a track where you know you don’t need to sprint across roads or other obstacles. A treadmill without any incline is a good choice.’
Hoggins’s advice: ‘Most people find it super hard to do zone 2 whilst running, so if that’s what you would choose, start with intervals of 1-minute running and 1-minute walking, and over time increase the running interval and lower the walking. Start with 30-minute sessions two or three times a week, then slowly build up to 40 minutes.’
Vincent’s advice: ‘This is my preferred modality for zone 2 training. One of the biggest benefits of cycling is that there is no impact, and almost everyone can cycle without issue. If you have your own bike, it might be useful to get a turbo trainer so you can do this indoors to focus on managing your breathing and looking at your split times. Avoid any resistance when you first get started, then gradually increase as it becomes easier.’
Hoggins’s advice: ‘Try an indoor exercise bike if you’re just starting out, as this will be easier than fighting with the weather and any incline or resistance outdoors.’
Vincent’s advice: ‘If you regularly practice cardio training, walking might be too easy for you, but you could add incline on a treadmill or try a hilly route to bring it up to a moderate intensity. For everyone else, start with a flat surface, then try an incline of 2 on a treadmill and increase in increments every week. If you prefer outdoor walking, find a flat route, then try some hills.’
Whichever modality you choose, it’s essential that you maintain a steady pace and incline. Any spikes will cause a spike in your heart-rate.
How long should a zone 2 training workout be?
If you’re a beginner, both Vincent and Hoggins recommend starting with 20-minute sessions, then gradually work your way up to 60-minute workouts. Remember that the key is to increase the durations in increments – there is no use in going straight from 20-60-minute sessions. Add 10 minutes every week, or every other week, and see how you go.
How often should you do zone 2 training per week?
‘I suggest doing zone 2 training 1-2 times per week,’ Vincent recommends. ‘This gives you enough exposure to the training type to see gradual improvements. Also, zone 2 training can often take up a more extended amount of time 30-60min sessions, so twice per week is enough when your sessions might be longer than, say, a HIIT class.’
Can you do zone 2 training every day?
If that's what you feel like doing, absolutely. It's low-impact and low-intensity nature means there is no harm in doing zone 2 training every day, but know that you will see results from doing it just 1-2 times per week, as per Vincent's advice above.
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