zone 2 training

Zone 2 Training

Deborah KayBy Deborah KayApril 3, 20196 Minutes

Zone 2 heart rate is when your heart rate is within 60-70% of your maximum heart rate.

Zone 2 Metabolic Training Zone is 70 to 90% of your anaerobic threshold or 20 bpm below your anaerobic threshold heart rate.


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 fiber 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


Other Resources

Peter Attia’s AMA 05 (Paywall)

  • 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)
  • So if your lactate threshold is ~2 millimolar… your aerobic peak is the speed you can go without going over 2 mm of lactate
  • At that zone 2 level, your blood glucose just generally starts to very slowly decline because you’re not really relying on it that much since you’re using fatty acid as well (you’re going to take the maximum efficient path to generate ATP)