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The Three Training Zones That Really Matter

The performance Project

Using Physiology to Better Understand Training Zones

Training zones. Most athletes know it can be useful to use training zones, but it can get confusing.  In the TrainingPeaks app alone, there are five different training zone options for running.  Some have five training zones, some seven, and even one with ten training zones.  So, how you do make sense of it all?


There are only three training zones when it comes to your physiology:

Moderate Exercise Domain

  • Includes zone one and zone two in a five-zone training model
  • Blood lactate and VO2 is at a steady state
  • Below the first ventilatory threshold (VT1)


Heavy Domain

  • Includes zone three in a five-zone training model
  • Blood lactate and VO2 increase but in a linear fashion
  • Between the first and second ventilatory threshold (VT2)


Severe Domain

  • Includes zones four and five in a five-zone training model
  • Blood lactate and VO2 begin to increase exponentially
  • Between VT2 and VO2 max





Lactate & VO2



1 – 2

Steady State

below VT1



Linear Increase

VT1 – VT2


4 – 5

Exponential Increase

VT2 – VO2 max



Understanding these physiological markers help athletes and coaches understand what the goal of each workout session is:


  • Workouts in the moderate domain are often described as ‘easy’ or ‘aerobic’ sessions. They help increase stroke volume and reduce exercising heart rate at the same intensity. 


  • Workouts in the heavy domain help improve lactate buffering capacity and improves speed or power at lactate threshold.


  • Workouts in the severe domain are high intensity sessions often with short but intense repeats. They help improve power and maximal speed. 





Goal of Session


Increase stroke volume


decrease exercising heart rate


Improve lactate buffering capacity


Improve speed or power at lactate threshold


Increase power


Increase maximal speed

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