Originally Posted by
chasm54
They are independent measurements, but as I understand it they are closely related. Essentially, FTP is the highest power output you can sustain for an hour or so. LTHR is the highest HR you can sustain for a similar period. So in theory, at a steady FTP we should see something close to a steady LTHR, or slightly higher.
Joe Friel's blog
Of course, they decouple. As you keep going at FTP, cardiac drift occurs and your HR may climb above LTHR towards the end of the session. Conversely, training as I do on HR, keeping my HR at the threshold level means that towards the end of the hour I am probably lessening the power. That's my understanding, anyway.
That is that idea I got as well when someone brought up having your power measured versus your heart rate. I would imagine that as you keep one steady one would have to fluctuate over time, unless we are dealing with a superb athlete or someone who has trained at a high level.
I did use this weekend to figure out a LT based on heart rate and found I am right around 157-159. At the heart rate I could sustain a consistent tempo/cadence and not slow down for about 20 minutes. I did this in an area with some very slight hills which was about 4.5 miles long. Once I got into the 160's HR-wise I was huffing and puffing and could only keep that up for a short time. I have found that my best HR range is 135-150 for any sustained effort over a period of time. I did a 36 mile ride and felt great. Also did it in less time than it took me to do it before.
I also felt great afterwards too.