I'd like to peel the onion one more layer on the subject of lactate threshhold HR (LTHR). Doing a 30 minute time trial on a trainer seemed like the best approach for me. My plan was to warm up, then go pretty hard for 10 minutes, and then see if I could keep that pace for the last 20. Several sources suggested taking the average of your last 20 minutes as your LTHR.
I have a Cardgirus trainer so I set up three, ten-minute intervals with no rest between them so I could use the built in features to see (afterward) my average cadence, heart rate and power for each 10 minute segment. My watts and heart rate for the each 10-min segment:
Watts Heart rate
Cadence averaged 92, a little lower than my typical 95-105 I use in my interval workouts. Since my power dropped slightly, it looks like I was trying pretty hard (it seemed like it at the time). My heart rate hit a plateau and was still creeping up at the end so I'm wondering if I couldn't have gone harder (which I think might be possible).
How would you interpret this data in terms of LTHR? How could I do the test differently to get results more clearly indicative of LTHR? It sounds simple to do a "30 min time trial" but the devil's in the details.
I'm 45 years old.
Dave Palese replies:
It sounds like your testing protocol is pretty sound:
 the conditions are controlled
 the conditions are repeatable
 and you can use the data gathered to help fine tune your training
If you would rate the effort for the final 20 minutes as a 9 or so out of ten, I'd say you gave it your all, and would average the average HRs from the last 2 segments, for an ESTIMATED LTHR of 162.
It is important to realize that any field test, like the one you used, will only yield an estimated LTHR. You aren't dealing with exact numbers. But for the purposes of training, the numbers you get from such a field test will work just fine when defining the heart rate ranges for your intensity zones.
It is important that you repeat this test periodically. Most test results are useless if the test is only dome once. I suggest repeating this test every 8-12 weeks to chart your progress.