What Is Efficiency Factor and Decoupling?

If you really want to geek out your training, these are two new additions to the Training Peaks software, however these figures can be calculated manually if you do not use TP.

Joe Friel explains the Efficiency Factor (EF) here:

"We have known for decades that if heart rate during an all-aerobic (below lactate/anaerobic threshold) workout rises while the intensity (power or pace) stays the same, then the athlete is not operating efficiently and his or her aerobic endurance is questionable. The same is true if heart rate stays the same and power decreases or the pace slows." - Joe Friel

To calculate EF, find your normalized power (or normalized pace) and divide that by your average hear rate for the workout.  With this ratio, you can compare it to similar workouts to see changes in your aerobic efficiency.  The key is to use workouts that are very similar.

"To be reliable, the workouts need to be quite similar by making sure all of the elements are alike. This includes level of pre-workout fatigue, equipment, course, weather conditions, altitude, pre-workout nutrition (especially stimulants such as caffeine), warm-up and perhaps even time of day. The more similar all of these are from one session to the next, the more valuable the information is. If you are making good aerobic progress, then your EF will rise over the course of a few weeks." - Joe Friel

I ride a similar training route during the summer, so I will use EF to compare to similar workouts to see if there is improvement in my efficiency.  I will also use it to compare race performance to previous years.  Again, being conscious of changes in elements, etc.

Decoupling is a percentage change based on your EF from the first half of your workout to the second half of your workout.

"This is a way of measuring output-input relationship changes that take place during a workout or race as a way of determining aerobic fitness. For this metric to provide useful information the workout or segment must have been fully aerobic (below the lactate/anaerobic threshold) and steady (low Variability Index).

I like to see athletes achieve a decoupling of 5% or less (negative numbers are, of course, less than a positive 5% and may reflect outside variables such as warm-up and weather but are assumed to be good results). As with EF, there are many variables that affect decoupling. These must be controlled."  - Joe Friel

Below is Friel's explanation on how to interpret the data:

"Generally speaking, if an athlete’s decoupling is consistently 5% or less for steady-state aerobic workouts, then his or her aerobic endurance is sound. For example, if you quit training for a while your decoupling will reflect your loss of fitness. This will be obvious as an increase in fatigue late in the workout causing either heart rate to rise or power or pace to worsen—or both. In either case, decoupling will rise above previous values for the same workout and may result in decoupling of greater 5%, indicating a need for more aerobic training."  - Joe Friel

I can definitely see how decoupling can help my training and I'm glad TP calculates this data for me.