Zone 2: Steady State Endurance Training Explained
Zone 2 is perhaps the most talked about training zone
Both the scientific literature and anecdotal evidence from both amateur and professional cyclists suggest that polarized training models are often the most optimal means of distributing training intensity to achieve long-term improvements.
With this understanding, Zone 2 is the intensity range you’ll likely be spending the vast majority of your training time in, so it’s a crucial part of your training program to get right.
What Is Zone 2?
Zone 2 most commonly refers to the 2nd zone in a 5 zone scale.
It’s a lower intensity training zone that’s a step up from a pure “recovery” intensity and one below a “tempo” intensity in the 5 zone model.
Zone 2 is where the highest stress is put on the mitochondria to oxidize fat for fuel. The ability for our body to oxidize fat for fuel and re-use lactate as a fuel source will directly determine our performance as endurance athletes.
This zone is very specific. Two low and our body’s won’t release enough catecholamines to elicit physiological changes in our training. This is zone 1. Too intense, blood lactate will accumulate and inhibit our ability to oxidize fat for fuel. Zone 3 and above. There is a time and place for zone 4 and 5, but when doing your long steady state days, zone 2 is a specific zone that you need to stay in!
How Is Zone 2 Calculated?
Zone 2 can be most often calculated as a % of a threshold value, commonly Functional Threshold Power or FTP (for cycling), as well as a % of Maximum HR (MHR) and rating of perceived exertion (RPE).
Calculation:
Apply the following %s to whichever value you choose to use (power, HR or RPE):
55-75% FTP
60-70% MHR
3-4 out of 10 RPE (can recite the alphabet without taking a deep breath)
As an example, let’s take an athlete with a 220W FTP and 180 BPM MHR:
55-75% of 220W FTP = 120-165W
60-70% of 180 BPM MHR = 108-126 BPM
Zone 2 Training Benefits
Mitochondrial Content
Training for sustained periods at a Zone 2 level helps to increase mitochondrial density within the Type I (slow twitch) muscle fibers. Mitochondria produce energy (ATP) and aid in lactate clearance. The more mitochondria in the muscle cells, the better an athlete can perform at submaximal levels.Capillary Density
Zone 2 builds capillary density around the Type I fibers. Capillaries are the blood vessels or “pipe work” that deliver oxygenated blood to the muscles and remove metabolic byproducts from the muscles. More capillaries tend to result in greater the delivery of oxygenated blood (a large part of achieving a higher VO2max) and greater clearance of substances linked with fatigue.Cardiac Adaptations
Important cardiac adaptations are also stimulated by training in Zone 2 for sustained periods, such as stroke volume (the amount of blood that is pumped out of the heart per beat).
Higher “MFO” or Maximum Fat Oxidation
Through development of the Type I muscle fibers, Zone 2 training helps to improve endurance by increasing the maximum power output at which you can still burn mostly fat for fuel or “Maximum Fat Oxidation”. This is of extreme importance for endurance athletes, since fat is a far more abundant fuel source compared to carbohydrate.
Below:
Zone 2 would be the apex of Fat oxidation. You can see natural progression of fat oxidation and why lower intensity is not better along with higher intensity. It’s a sweet spot and it is very different for each individual regardless of what your Vo2 max is.
Common Questions:
“How often should I train in Zone 2?”
The quantity and frequency at which you might train in this intensity zone will depend on several factors.
Time, how much time do you have?
Fitness or racing goals
Training history
Professional athletes train zone 2 at 2-4 hours a day, 5-6 days a week. or 20 hours a week.
For the average individual who has a job this is not likely, also, you are not as fit as these individuals so you do not need the same amount of stimuli to benefit from this training. But that said, regardless of recommendations, the true answer is MORE. You cant overtrain zone 2 like you can with interval training. (assuming sleep and nutrition is adequate) the longer your bouts and the more often they are the better.
When trying to improve your zone two, the more days a week the better, let’s say you have 4 hours to train zone 2. Four, 1 hour sessions would be best.
When trying to maintain zone two, and spend more time lifting weights or interval training, 2x a week is adequate to maintain. I would recommend 2, 90 min bouts per week. use a weekend day as the session is longer and maybe one week day.
For cardiovascular and neurological health the CDC guidelines along with other numerous scientific literature recommend 150 min a week, for the average person.
“How long should Zone 2 training be?”
45 min absolute minimum. An hour or more is ideal. To induce the desired adaptive stimulus sought from this form of training, exercise will need to be somewhat long duration to cause some level of fatigue in the Type I fibres, and deplete muscle glycogen stores to a reasonably low level, therefore stimulating fat oxidation even more.
If I have clients who don’t have an hour to train, I recommend to resistance train or do speed/power work (numerous 5-10 second sprints all out, with cool down) . When time is crunched find something that will work for that time slot.
One trick, when short for time, train zone 2 fasted, (less than 90 min training session) you will tap into fat oxidation sooner and argubally benefit more from the cardio session. Read about carb restricted training here
”What’s the best cadence for Zone 2 training?”
There may be some benefit to slightly higher cadences during some Zone 2 training sessions given that there is some evidence linking sheer amount of muscle contractions to the relevant adaptive stimulus.
The average person can generally elicit a higher Maximal fat oxidation from running/walking compared to machines like rowers or bikes. There are many biomechanical reasons for this but one is simple math of cadence. Runners have a higher cadence then cyclists or rowers.
When looking at work output I like to divide the reps x power. Let’s say you pedal 200 watts at 100 RPMs. If we lowered that to 50 RPMs you would need to double the power per stroke to still maintain 200 watts. Try the “ERG” mode on your trainer, change cadences at a given wattage, and you will feel what I mean.
200 watts at 90 rpms is very different than 200 watts at 50 RPMs.
The less intense we can make each stroke the less intense the exercise and less carbs are needed and more energy we can derive from fat and therefore spend more time in zone 2.
”What’s the best way to stay in Zone 2?”
Due to variables like terrain, weather and also riding style, it can be difficult for some cyclists to accumulate the necessary time in the correct intensity range during a Zone 2-focused ride. To help with this, here are a few suggestions:
(best answer) Train zone 2 indoors on a trainer, it will be the most efficient and effective way to spend your time.
(If you must train outside) Try choosing training routes that are flat or have shallow rolling hills
Avoid high traffic areas which result in stop-start riding to the best of your ability
In hilly areas, consider easier gear ratios, so that intensity can be kept necessarily low on steeper gradients
Average Heart rate does not represent time spent at that hr)
Example: Let’s say your Zone 2 heart rate is 130 Bpm and you did a 2 hour ride with hills. Your HR monitor at the end of the ride says your average hr for the ride was 130. This DOES NOT mean you were in zone 2 the entire time. In addition, technology now gives us our power zones on the apps we use. We can directly put in our personal zones if we know them: zone 1 HR 100-125, zone 2 HR 125-135, zone 3 135-145, ect….
After a ride your device may say, you spend “x” amount of time in zone 2, “x” amount of time in zone 3. This is also false. The only way to tell what zone you are truly in is to work out with a direct calorimeter or take blood lactate throughout the ride.
But why?
Heart rate and watts are simply estimates of where our bodys are biochemically, not direct measurement. Heat, core temp, hydration status, blood volume and blood lactate can mess with these numbers. The exception is if you were inside on a trainer and pedaling at the same wattage at the same HR for an entire 90 min. Then yes, this would be an accurate representation of your zone that session. This is because you never left that zone you were training.
Take a hill climb for example. We’ll say you are going for 8 min and its near maximal, zone 4 work. Your blood lactate levels would be near 6-8 mols at the top of that hill. The next 5 min your heart rate and watts may go down to zone 2, but your blood lactate will stay elevated for another 20 min, inhibiting fat oxidation and the purpose of zone 2 training for the majority of that time.
This is where your specificity of training needs to come in. Are you training intervals today? or are you training zone 2? Or are you just having fun and don’t care? It does matter the reason, I just want you to realize that the devices we use don’t always give us accurate data. So when training “zone 2” specifically, try not to venture outside of zone 2. Train with a purpose!