Zone 2 - Notes

image of runner and heart

I've decided to commit to focusing on Zone 2 training to build my aerobic base in 2024. Here are some notes and resources:


Everything below is just pulled from resources such as these. These are all fantastic:

Peter Attia and Iñigo San-Millán

These 2 interviews are a gold mine of in depth information on this topic. Fascinating, but a big commitment to get through!

A shorter, but very technical overview from Iñigo:


Great overview article:

"How to Build Your Aerobic Base" -- Nice video with useful tips


Build your Aerobic Base

  1. Increase the capacity of your aerobic energy system which relies on oxygen to convert fats and carbohydrates into energy
  2. Your body becomes more efficient at using fat as its fuel source primarily by increasing mitochondrial density in the cells and improvements in the efficiency of enzymes involved in the fatty acid oxidization pathway
  3. Can perform at a given intensity for longer without fatigue by increasing the threshold at which the body switches from the aerobic system to the anaerobic
  4. Body becomes more efficient at clearing lactate and utilizing it as fuel, which aids in quicker recovery within a workout and between.
  5. Improved immunity - the breakdown of free radicals occurs in the mitochondria. So having more mitochondria and being in better shape means your body is more capable of controlling free radicals.

Why do we care if we're using energy in the aerobic vs anaerobic zones?

  1. If your body is not efficient at using its fat stores for energy, it must rely heavily on the glycogen stores. This is a less abundant energy source that leads to quicker fatigue during physical activity.
  2. Lactate will accumulate at a lower intensity threshold, reducing the ability to perform at higher intensities
  3. More likely to burnout and get injured when relying on high-intensity/anaerobic systems
  4. Daily activities can be more challenging if your aerobic system is not developed enough and you need to use the anaerobic system frequently.


How do I know I'm in Zone 2?

There are multiple guidelines pointing to how to target Zone 2:

  1. Nasal Breathing
    • Workout at a pace that you can breathe only through your nose. If you feel the need to breathe through your mouth, slow down or walk for awhile to return to nasal breathing.
  2. Conversation test
    • Workout at a pace that you can sustain a conversation with someone the entire time - but hard enough they know that you are working out.
  3. MAF Formula
    • The MAF FormulaThis is a formula that uses 180 - your age as a starting point and makes adjustments from there based on your fitness and overall wellness levels.
  4. If you have a heart rate monitor:
    • 60-70% of your max heart rate
  5. If you have a heart rate monitor and know your VT1 threshold (got mine with a VO2Max test last summer)
    • Stay below your VT1 threshold
    • For me this is only 1 bpm higher than 70% of my max.
    • I believe as one gets more aerobically fit the VT1 threshold will increase and over time becomes a better Z2 upper limit than 70% of max hr.
  6. Stay below 2 mmol of lactate levels in blood
    • Most accurate, 70% of max hr and vt1 thresholds are approximations of this
    • This is pretty hard to measure since continuous lactate monitors aren't really an accessible thing yet.
  7. I've seen others as well

For me, as of Feb 2024 -- I have to walk for 80-90% or more of a 45 minute run... (Update -- after just a few training sessions I'm running -- slowly -- much more than walking). I sync my heart rate into my running app and if I see it go over my threshold I switch to a walk, and when I get about 15-20 bpm below my threshold I start running again. Usually for only a very short time before switching back to a walk.

UPDATE APR 2 20424
In early March I bought a Polar H10 chest strap heart rate monitor as I had begun to not trust the wrist-based heart rate monitor on my Whoop band. Turns out the Whoop was overestimating my heart rate consistently by 20 bpm (sometimes by up to 60 bpm!). With an accurate heart rate monitor I now know I can maintain a zone 2 heart rate currently at an 11:00 to 12:00 pace for an entire run.

How often

Sounds like 3-4 times per week of at least 45 minutes per session is a good starting place for beginners to be at or work to.

Tracking Progress

I've started a Google Spreadsheet that I enter my total time, mileage, avg pace, and avg hr into and compute a Run Efficiency score from which tells me meters / heartbeat I was able to average over the run.. Hoping to see that go up which over time will mean a faster pace at the same heart rate.

I am also going to start trying out the Strava app - it looks like there are a lot of built-in graphs to track this as well.


  • How much does the cold affect my zone 2 performance? So far I've been running only on very cold days and can't believe how poorly I've done. Very likely that's mostly because I have a very poor aerobic base, but wondering if the cold is making it even worse. Update: It was likely just the poor reporting of the Whoop
  • Does coffee in the hours before the workouts negatively affect zone 2 performance?
  • How quickly will I notice improvements?