Hey,
I have been analyzing my data from 2020. Efficiency Factor is something I would like to better understand. I know that it equates when Training Peaks computes HR to power over the course of workout or ride. That data point then provides a number that can determine your endurance. After looking at rides, my EF ranges from 1.0 to 1.8, sometimes higher and or lower. Is there a range that is followed to determine what’s good and what’s bad. Based on my research in TP, the higher the number the better your endurance but I’m not sure which way? What do I also need to review when looking at this data metric? Insight appreciated!
Hey Jeff!
Glad to see you analyzing your data, this is one of the biggest things athletes can do to understand their training, recognize their weaknesses and improve their ability to FtFP 
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You are correct in that an increase in your efficiency factor (EF) indicates improved endurance and can be used to compare your fitness over the course of the season (especially during the “on” off season). It is one of those metrics though that varies greatly based on the workout, weather, terrain, ride length, etc. Ideally to measure it accurately you should perform the same workout, on the same bike and on the same route and then compare them. Here is an example
Ride 1: 180w (normalized power) ÷ 135 bpm average = 1.33 EF
Ride 2: 190w (normalized power) ÷ 132 bpm (avg) = 1.48 EF
EF Improvement = 11%
Aerobic Decoupling is a similar metric that compares the EF from the first half of an activity to the second half. A lower change in EF (< 5%) from the first half to the second half can also be a sign that your aerobic endurance is improving. Again, this metric varies based on the terrain, ride length, workout type (e.g. a ride with SS or threshold will likely have more decoupling than an endurance ride), etc.
That being said, you can do a zone 2 ride and look at your decoupling after 2 hours into the ride and at 3 hours in. Then follow your training plan and look at that decoupling for an equivalent 2-3 hour zone 2 ride and see if you decouple less. Again, less than 5% is ideal!
Hope that helps 
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That is extremely helpful. Thank you so much for the detailed response. What I now understand is that you have to compare apples to apples and not comepare dissimilar rides/workouts.
Aerobic decoupling is the metric I should look at when doing post ride analysis. This was another area that I briefly reveiwed. So I thank you for going into detail in response to my question and adding further info to look at the big picture. Thank you Lacey!
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