There are a few boxes that need to be checked off before we can say your base phase of periodization was a success and you are ready for the build phase.  One of these boxes that I like to ensure is checked off for my athletes before progressing them is aerobic coupling.  Aerobic coupling is looking at how much fluctuation in heart rate there is when maintaining a steady power output.

Example of being aerobically coupled

Being aerobically coupled means there is less than a 5% increase in heart rate for a given power output.  Here is an example of what aerobic coupling looks like:


The red line is heart rate, and the purple line is power.  This athlete performed 2×20 minutes at Tempo Zone.  As you can see, the power and heart rate stayed consistent for the entire 20 minutes.  The first 20 minute effort was performed @260w with a heart rate of 160 BPM (power to heart rate ratio = 1.625).  The second 20 minute effort was also performed @260w with a heart rate of 164 BPM (power to heart rate ratio = 1.585).  So, the heart rate did climb slightly, but the decoupling rate was only 2%.  This athlete is ready for their build phase.

Example of being aerobically decoupled

Now, check out this athlete’s workout:


This athlete also performed 2×20 minutes at Tempo Zone.  So, a few things jump out to me right away and are pretty clear to see.  1. The heart rate (red line) is nowhere as consistent as the coupled athlete’s was.  2. During the rest period, the heart rate really never went down.  3.  The second 20 minute interval you can see a gradual increase of heart rate while the power stays steady.  So, by the numbers, the first 20 minutes was performed @195w with a heart rate of 147 BPM (power to heart rate ratio = 1.323).  The second 20 minute effort was also performed @195w with a heart rate of 157 BPM (power to heart rate ratio = 1.242).  This athletes decoupling rate is >6%.  Back to Sweet Spot work, buddy!

How can I determine my aerobic coupling?

I like to have my athletes perform a 2×20 minute effort at Tempo Zone with an 8 minute rest, ideally on their trainers so they can focus on a consistent output and not have to deal with changes in grade.  Then, once you have the data…

  1. Divide the power by the heart rate for the first interval.
  2. Divide the power by the heart rate for the second interval.
  3. Subtract the first interval’s power to heart rate ratio from the second interval’s power to heart rate ratio.
  4. Divide this number by the first interval’s power to heart rate ratio.

So, for the second athlete’s aerobic coupling test I did…

  1. 195/147 = 1.323
  2. 195/157 = 1.242
  3. 1.323-1.242 = 0.081
  4. 0.081/1.323 = 0.061 = 6.1%

So, are you ready to progress to the build phase of training?  This depends on a few factors, but I like to make sure my athletes are aerobically coupled before progressing them to the higher intensities and greater training stresses that the build phase holds.  If you are aerobically coupled, congratulations!  You may Pass GO and collect your $200 dollars.  However, if you are aerobically decoupled, I recommend spending more time working in your Endurance, Tempo, and especially Sweet Spot Zone so you can reach new heights during your competitive and peak phases.

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Shayne Gaffney

About the Author Shayne Gaffney

Shayne holds a bachelors degree in Health Science in Professional Development and Advanced Patient Care, is a licensed physical therapy assistant in Massachusetts, a USA Cycling Level 1 (expert level) certified Coach, a USA Cycling Power Based Training certified Coach, Precision Nutrition Level 1 certified Coach, a US Military Endurance Sports (USMES) affiliated Coach, and USA Olympic Committee Safe Sport certified. He is the Founder of GC Coaching, Workout Content Editor at Zwift, the creator of P2 Coached Computraining, and the creator of Zwift’s “Build Me Up”, "Pebble Pounder", and "201: Your First 5K" Flexible Training Plans. He has been published in Bicycling Magazine, the TrainingPeaks blog, and Zwift Insider. He can be contacted directly via


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