Heart rate decoupling - lower heart rate after ~1h


With the use of Intervals.ICU I’ve noticed that my heart rate at a given power target is generally lower during the later parts of a 2-hour workout. Intervals.ICU calls this decoupling. Below are a few of my workouts recently with my heart rate and power output compared. This negative decoupling seems illogical to me, as I’ve always been taught that the heart rate should increase relative to the power output. Does anyone have any ideas as to why this might be?

The pink number is the 1st half
The orangeish number is the 2nd half

I’ve experienced the same thing on rides like Boarstone and Koip, but also outdoors.

One theory that I’ve worked with is if it depends on fiber type recruitment. I’m anaerobically inclined and possibly a large portion of my fast twitch fibers engage early in the ride. As the ride progresses I become more fat dependent as my slow twitch take over. I know it sounds far-fetched so if anyone has another reasonable explanation I’d be happy listen.

Just a couple of comments about the circumstances when you can reliably use heart rate decoupling (as I understand it anyway)

First - it should be very consistent endurance paced rides. This eliminates a bunch of the data you’ve posted here as many of these rides include intervals of various sorts (Tallac, McDuffie, Pisgah, English)

Second - you need 2+ hours to get reliable numbers

Not to say you don’t have a bit of an edge case in your HR tracking - but do you have data from a 2.5 or 3 hour endurance ride on the trainer such as Conness or Koip?

For reference - this is my decoupling information from Fletcher (90 minutes endurance) this morning


Whereas this is my decoupling information from a three hour version of Koip that I did this past weekend


Finally - a 2 hour sweet spot workout I did yesterday shows the same thing you are seeing - but isn’t valid due to the nature of the workout



Yes, you make great points. The decoupling metric it was originally introduced to track “aerobic endurance” over a month or two of early base training. The long slow distance type of base training. So that means it was designed to help you understand increasing endurance/fitness on steady-state aerobic rides (60-70% FTP).

For those new to reviewing decoupling data, I’d recommend mostly ignoring it or only using it on long (2+ hour) aerobic endurance workouts.

@philan that leaves only Baxter:

however even then I’d caution that Baxter doesn’t fit the original intent of decoupling because:

  • it is only 90 minutes
  • the cadence changes will likely drive heart rate changes and therefore it is NOT a good steady-state endurance ride for using decoupling
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I’ve noticed a similar trend in negative decoupling on endurance rides. The amounts seem insignificant (-1% to -2%)and not worth paying much attention too. A couple things I’ve attributed the negative trend too… Consuming simple carbs during an early AM ride. Room temp. falling as a result of windows being open and fan drawing in colder outside air. Increasing/improving hydration levels during a ride.(This is noticeable)

Probably some other things going on as well but the hydration component seems to be very noticeable as does decreases in room temp.