Why is my LT dropping?

ana61670 said:

I am searching for answers as to why my LT has been dropping.... .

What do you mean by 'LT dropping'? Are you having trouble reaching a certain target HR? Is your sustainable power dropping? Is your speed on a certain climb you do a lot getting slower? I take it you're not out pulling and analyzing blood samples as you ride so exactly what do you mean by 'LT dropping'?

If it's just difficulty achieving a certain target HR then it might just be fatigue from the classes or you might be adjusting to the training and you're not working as hard to maintain the same speed or a number of other possibilities. I'd probably start by looking at overall training load, rest and nutrition to see if the classes are leaving you too tired to train as hard as you'd like.

-Dave

Yes, I am having trouble reaching a certain heart rate. This is the second session of these classes and my LT went up three beats; about five weeks into the the second session of these classes I was unable to reach my LT, despite my efforts to do so. This was the first time it happened. In the last two weeks, its been basically the same.
Its quite possible, as you said, that I am not working as hard due to rest and/or nutrition, perhaps holiday stress :eek:
Race day is this week, I will make sure I am well rested.
Thank you for your reply.

Just curious, but what HR are you trying to reach? Are you using some generalized definition of LT HR as 85% of your true max HR? EG, if your max HR is 183, your LT would be "around" 155 bpm. When you say your LT "went up three beats", what do you mean?

Without tracking your level of power output along with the HR, it's difficult to know what's going on. If you're producing the same power at a lower HR this week, that would indicate that your fitness is improving.....which is exactly what should be happening with your training.

My LT was 175 during the first 8 week session of class; at the beginning of the second session of the 8 week class my LT had improved by 3 beats; to 178. This is the number I am having difficulty reaching and surpassing for certain efforts during our training.
Unfortunately we have no way (our bikes stink🙁) of measuring/tracking power output.
I was under the impression that by driving out LT numbers up we would be improving our fitness levels.
Thanks for your reply.

ana61670 said:

...I was under the impression that by driving out LT numbers up we would be improving our fitness levels....

Well if you can drive up the power that you can generate at your 'LT' then yes you've improved your fitness. But heart rate isn't really the same thing as LT and in general HR won't move upward much over time and ideally for a fixed power output your HR should drop over time.

Trouble is the bikes you're working on don't let you control the power output so it's very likely you're working much harder now then when you started and your fitness has indeed improved. But tracking HR alone can't tell you for sure whether that has occurred, you've got to monitor intensity (power) in some way to determine whether you're working at the same or higher intensity level for the same HR.

The other problem with HR is that it varies day to day and session to session for a lot of reasons including: hydration, cooling, nutrition, emotional state, fatigue, etc. A few beats here or there really don't mean much from session to session so I wouldn't beat yourself up too much over the lower HR you're seeing recently. It could be as simple as less cooling in the building or you're not as well hydrated when you arrive and isn't enough to tell you whether your fitness is suffering.

Bottom line, it sounds like you're still finishing the sessions and getting in some good training. Do what you can do, don't get too hung up on a few beats difference in HR from session to session and see if there are ways to loosely keep track of intensity (like how many turns you tighten up the resistance belts on your spin machine or what 'level' you dial into your gym bike or how many Calories the electronic bikes tell you you've burned in your session or per hour) if your intensity goes up (you're able to pedal the same or faster into more resistance) and you're completing the sessions then your fitness is improving even if your heart beats a bit slower or faster.

And although your spin instructor might use 'Target Heart Rate' and 'LT' interchangeably, LT can really only be determined by blood draws and then there's finer distinctions like LT1 for the initial rise (typically 1mmol above baseline blood lactate levels) or LT2 (dubious inflection points in the blood lactate vs. power curve or definitions like Mean Lactate Steady State or Onset of Blood Lactate Accumulation). Even the published studies have to clearly define what they mean when they use these terms rigorously so just for the record whatever you're tracking during your spin bike sessions it's not LT.

-Dave

ana61670 said:

My LT was 175 during the first 8 week session of class; at the beginning of the second session of the 8 week class my LT had improved by 3 beats; to 178. This is the number I am having difficulty reaching and surpassing for certain efforts during our training.
Unfortunately we have no way (our bikes stink🙁) of measuring/tracking power output.
I was under the impression that by driving out LT numbers up we would be improving our fitness levels.
Thanks for your reply.

Where to start... First, we don't yet know why you are calling 175 your LT, but 175 is very high for an LT heartrate (to the extent that there is such a thing). I assume you didn't get a blood test to determine your LT, right?

Whatever test protocol you used, your training environment has likely changed since then. In that case, there are all sorts of reasons you might not be able to reach a heart rate of 178 -- temperature, time of day, etc. It's unlikely in such a short time span, but even training can lower your max heart rate since when your heart grows in size it can't beat as fast.

Finally, "driving up your LT" seems like a pretty dubious training goal. How about driving up your power at LT? Also, it sounds like what you are actually doing is driving up your max heart rate not your LT, and this strikes me as really not a great training goal (it's probably not even healthy).

Ana, heartrate doesn't mean performance. It is just one of the many ways you can gauge the effort the body is producing (and a relatively inaccurate one at that). I haven't trained by heartrate in almost 10 years, but when I did, mine varied significantly. My averages during threshold efforts would be anywhere from 175 to 187. (It trended lower when my fitness was higher).