A few months ago, I was introduced to Zone 2 training by a colleague as a way to improve my cardio levels. For the past decade or so, I have solely been doing fast and short runs of up to 5km and intermediate runs of up to 10km, all of which were at heartrates of over 180bpm. Intrigued by this concept of running slower, I started to dig into the world of Zone 2 training and came to the realisation that I have simply been running wrongly pretty much my entire life.
Determining Zone 2 HR
Eager to enter the world of Zone 2 runs, I first calculated my Zone 2 heartrate using the simplest method of 60-70% of (220 – Age) which translated to around 130-135bpm. Sounds alright, until I had my first run and found the pace to be unbearably slow and weird. Researching further into the heartrate zones, I came across the Karvonen method and the MAF formula which seems more realistic compared to the traditional method which just uses a blanket formula for everyone based on age alone.
To make things simpler, I adopted the MAF formula while keeping Karvonen in mind as that would give me some range to push my heartrate higher when required. The pace was still slow after allowing my heartrate to rise higher, but slowly over time I found that my pace is improving while keeping within the same heartrate range. The improvements were minor and inconsistent, which may then be explained by environmental factors such as temperature or humidity or simply how well hydrated I was.
Intervals
When you start to dive into new interest topics, the algos pick it up real quick and start to recommend related topics to you. Enter intervals training, where you sprint for a distance and then slow down to rest for a short period before repeating again. Using AI as my running coach, I followed a training plan “tailored for me” based on the data I have been feeding to it and a weekly intervals session was recommended. I started off with 400m sprints and 200m walks which felt kind of easy so the next step up was 800m sprints and 400m walks. This was manageble for the first few sets however the 400m walk was not sufficient to bring down my heartrate in time before the next set, so the subsequent sets suffered and often gave me stitches. Nontheless, my AI coach advised me to push ahead, raising the stakes to 1000m sprints. This is simply disastrous advise as 1000m was simply too much and I could barely make it past 5 sets before having to cut the training.
Dropping back down to 400m sets, I repeated the intervals training for a while before concluding that there was not much improvements and back to the drawing board with my AI coach we go.
Serious Zone 2 Training
One of the key principles of Zone 2 training, or any kind of training, is to commit to it instead of jumping around various training strategies. I agree with the saying that Zone 2 may not be the best training method but it would be a good way to massively increase my mileage without sacrificing my recovery time. The only downside is that I spend way more time running than if I focused on intervals or just doing fast runs.
Around March of this year, I decided to try raising my weekly mileage by incorporating long distance Zone 2 runs of around 15km and above. If I could sustain this over a month and see improvements, this would prove that the method works for me. Fast forward a month, not only did this produce improvements to my pace, it also did not require long recovery periods which I needed after my all out sprints. For reference, take a look at the chart below of all my runs YTD.
Each dot represents a single run, with longer runs having larger dots and the color represents the heartrate ranges, ranging from light green all the way to red for higher heartrates. The X-axis represents dates while the Y-axis represents running pace. With this visualized, we can see that my fast runs are capped at slightly under 5min/km and these are all small dots representing short runs. Around mid march, I started committing to long runs and here we see the first run with a light green dot at around 8:20min/km. Not too fantastic but not too bad either.
I was also preparing for a 5.6KM race in mid April, so I had to occasionally throw in some faster runs too, which is fine as long as it does not take up too much of my weekly mileage. Repeating the runs week by week, the pace consistently improved bit by bit. The larger improvements came with the switch to MAF/Karvonen method as you can see with the yellow dots. Well strictly speaking this may not be an improvement at all since the heartrate zones are not exactly the same but from a pace perspective it is still an improvement.
The key thing to note is that by piling on more and more mileage each week, even at slightly higher heartrates, this promotes consistent cardio stress which the body then has to adapt physically provided there is sufficient rest time to recover. If we look at the May runs, we can clearly see that there are some green and light green dots amongst the yellow dots.
This means that my body has adapted to allow quicker pace runs while staying in the same heartrate zones. This was the affirmation that I was looking for. Fast forward again to today (14th June), my 21km run recorded the fastest pace ever at 6:51min/km, which is a cool 8 seconds per KM faster than last week and over a minute faster than when I first started doing 21km runs. The graph above would show a clear trend moving to the upper right direction, meaning that over time my pace is improving bit by bit, week by week.