zone 2 training

Zone 2 Training

Deborah KayBy Deborah KayApril 3, 20199 Minutes

What is Zone 2

There are different definitions of Zone 2:

  • Zone 2 Metabolic Training Zone is 70 to 90% of your anaerobic threshold or 20 bpm below your anaerobic threshold heart rate.
  • Zone 2 heart rate can be approximated when your heart rate is within 70-83% of your maximum heart rate. Aim for 75% of max heart rate.
  • Zone 2 is when you use slow twitch muscles, metabolizing the highest level of fat and stimulating the mitochondria.


Zone 2 Training and Energy Sources

When we exercise, we transform chemical energy into mechanical energy. Our muscles needs to synthesize ATP in order to contract. ATP is generated via anaerobic and aerobic metabolism.

Fats and carbohydrates are the two main substrates used for energy generation(with some contribution from protein).

  • Fat it is stored primarily in the adipose tissue but it is also stored in skeletal muscle in small amounts.
  • Carbs are stored in the form of glycogen in skeletal muscle (about 80%) and in the liver (about 15%).
  • Without supplementation, we can typically store about 1.5 to two hours of glycogen in our muscles.

The exercise intensity or metabolic and physiological stress as well as muscle fibre recruitment pattern will dictate whether we use fat or carbs for energy. Lower training zones allow your body use fats as fuel. As exercise becomes more intensive, you increase the demand for CHO.

  • Aerobic Exercise: means ATP demand is slow enough that it can be met through mitochondrial oxidation of fuel sources (fatty acids)
  • Anaerobic Exercise: Anaerobic energy demands exceed the capacity of mitochondria oxidation. Fuel source comes from stored ATP in the muscle itself – not requiring any energy systems. Anaerobic threshold (AT) is the heart rate at which your body transitions from burning primarily fat to using primarily carbs for energy. At this point, lactic acid begins to accumulate in the bloodstream faster than you can use it.


By training Zone 2, we will not only improve fat utilization and preserve glycogen but we will also increase lactate clearance capacity which is key for athletic performance.

(Sources: The science behind Zone 2 training, Why Triathletes Should Train in Zone 2)


Benefits of Zone 2 exercise

Fat burning and lactate clearance: “Zone 2 is the exercise intensity where I see the biggest improvement in fat burning and the biggest improvement in lactic clearance capacity.” –Iñigo San Millán, Ph.D (podcast interview with Peter Attia)

Glucose: There is no better way to stimulate glucose deposition into the muscle than via zone 2 training

Mitochondria Efficiency: Zone 2 stimulates different pathways for mitochondrial biogenesis as well as improves the efficiency of the mitochondria


What is the right dose of Zone 2 exercise?

Two days a week of Zone 2 exercise in elite athletes for many hours maintain fitness. For diabetics, Iñigo thinks 3x a week for an hour at a time is enough to be beneficial.

End with 5-10 minutes of high intensity exercise at the end of your Zone 2 to get the benefits of both energy systems. But it’s important to do it at the end because if you do it in reverse order, it will trigger the wrong hormonal responses and high blood lactate (which inhibits lipolysis).

An exercise session where you’re going in and out of different zones is NOT Zone 2 exercise.

A rough ratio should be 80% zone 2 and 20% zone 5 (i.e., max capacity. He believes this middle area of intensity (zones 3-4) is the least important zone to be training within

How to know if you’re in Zone 2

  • Measure blood lactate (2 mmol) – Zone 2 the highest level of aerobic output you can generate (i.e. what’s the greatest speed you could run on treadmill, or wattage on a bicycle, while keeping lactate below a certain level)
  • Measure fat oxidisation (Zone 2 is when max fat oxidisation occurs)
  • DFA (alpha 1) > 0.75 (between 0.75-1) – can be measured with the HRV Logger app and a Polar H10 chest strap
  • When you can hold a conversation the entire duration of the session but it feels a bit uncomfortable

Duration and Frequency

Maximum Zone 2 benefit comes from training 3-4 times a week with 1-1.5 hours each time.


Maximum Aerobic Efficiency (MAF)

MAF stands for Maximum Aerobic Function and combines exercise, nutrition and stress to build your aerobic system, the fat-burning engine responsible for fuelling all of the body’s needs. A well-functioning aerobic system leads to:

  • Burning fat for fuel
  • Increased energy and endurance
  • Run faster for longer
  • Injury and disease prevention
  • Improved brain function
  • Better health and fitness

The MAF 180 formula calculates your MAF Heart Rate to guide optimal aerobic development.

  • Your MAF Heart Rate is calculated at 180 minus your age
  • Subtract 10 for major illness, surgery, medication or hospitalisation
  • Subtract 10 if you are frequently injured, get 2 colds per year, have allergies or asthma, exercise inconsistently, or your athletic performance has plateaued
  • Add 5 if you are a competitive athlete training for more than a year without issues.

Source: MAF Method


Heart Rate Reserve

Take your maximum heart rate (220 – age).

Subtract your resting heart rate for your heart rate reserve. (This heart-rate reserve represents the cushion heartbeats available for exercise.)


Fat Burning Zone: This fat-burning range will lie between 50 and 75 percent of your heart-rate reserve.
Aerobic Training Heart Rate Range (for Fitness): The range required to improve aerobic endurance is higher than that needed for fat burning. It ranges between 75 and 85 percent of your heart-rate reserve.
Aerobic-Anaerobic Threshold Heart-Rate Range: 85 and 90 percent of your heart-rate reserve. This range represents the upper limits of aerobic exercise—the point just before you push yourself into exhaustive anaerobic work. Exercising at this intensity is usually done to improve athletic performance. It is not recommended for weight loss. Operating at this intensity level will not burn body fat. It becomes a carbohydrate (muscle-glycogen) burning exercise.
Anaerobic Training Heart-Rate Range: 90 to 100 percent of the cushion of your heart-rate reserve. The goal here is to go as fast as you can for as long as you can. Pure anaerobic, carbohydrate-burning, exhaustive, lactic acid-producing exercise.

Source: How to Calculate Your Training Heart Rate Zones



Comparison of Heart Rate Zones

Heart Rate Zones















#201 – Deep dive back into Zone 2 | Iñigo San-Millán, Ph.D. (Pt. 2)

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