Does a change in treshold affect Loads and Fitness?

This may be a stupid question, but I can’t quite wrap my head around it. I’m a runner and two years ago I had my lactate levels measured. I’ve set my training zones, as well as the HR and the pace thresholds based on those results.

Now I got the levels measured again, and while the HR threshold only had a change of a couple of bpr, the pace threshold changed quite drastically even.

Does this and/or how does this affect my Training loads and the Fitness graph? I use Pace/HR/Power as my training load priority, so I presume it does affect some how. Is there some best practices I could or should do? Is this simply something I should keep in mind when comparing the the future Load to the prior Loads? Will it now make the Fitness graph look weird for the next 40 days?

I’m just finishing my so called “pre-season” and starting the actual training plan, so the timing is alright in any case. I’m also nowhere near a pro or anything, so I’m sure I’ll live, but I’d appreciate if I knew what to keep in mind moving forward!

If you use Pace (or Power) for Load calculation, this will absolutely make a difference. Load is calculated from the delivered Pace (or Power) referred to the Threshold Pace (or Threshold Power).
If you haven’t changed your Pace threshold during all that time, and your Threshold Pace has increased drastically, all your runs have over-estimated load because you evolved to higher paces at same ‘effort’ and thus the intensity (which is referred to your threshold), became mathematically higher and higher while you were not feeling greater effort.
An example:

  • If you used to run at 80% of threshold right after your first test, that session would return 0.8 squared times 100 = 64 TSS load
  • If you run now at what was before Threshold and you did not change your threshold pace, the intensity is 1 and the load is 100TSS.

If you use HR to calculate Load, the difference will be less. But HR load is failing for short bursts. The choice of using Pace for Load calculation is great, but you need to test and update Threshold Pace every couple of months to stay accurate with load calculation.

If you have an idea of how your threshold pace evolved, you can go back in time and modify the threshold pace, then re-analyse the activities, to et a better load indicator.

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Thank you for your reply and for the suggestion! I had not really expected the threshold pace to change anywhere near as drastically and as the tests are quite expensive, I had just skipped it.

Anyway, I did exactly as you suggested, and edited my earlier workouts, which was easy enough cause you can do it in bulk. I’ve shed about a minute off from my test two years ago, so I just did some sort of a guestimate on the gradual progression. That around this time of the year last year I was half a minute slower, and that after the winter season (when I run significantly less) I had a slower start in April and so on.

Obviously this won’t be very exact, but it should serve as some kind of a comparison point, and at least the fitness graph won’t look completely bonkers now. I guess the main thing anyway is to track the progress, so already editing April/May of this year close to the threshold pace measured this week should give a pretty decent tool for tracking progress this summer.

Thanks again!

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