VO2max decreases after long runs.

Herman,
Thanks for the message. A good explanation is done here as well
https://www.polar.com/blog/cardiac-drift-effect-on-training/

If, as you mention, cardiovascular drift is well taken into account and as such this kind of fatiugue is then not taken up in VO2max computation, why is then the points you obtain for a long slow run so low, or/and VO2 max for a long run often lower than for a run where you often run slow but still do a few tempo increases?
Somehow, I still feel that long slow runs are not well enough rated in terms of performance / status points or VO2 max considerations.

In defence of Firstbeat:
I have sometimes seen my VO2Max go up after a long, slow run where my Performance Condition was negative during most of the run. I suppose this is caused by the Firstbeat algorithm comparing my actual decrease in Performance Condition to my expected decrease and rewarding me for having a lower actual decrease than expected.

But in general I agree. The Firstbeat algorithm does seem to punish my slow runs. Of course, this could mean that I have a heart rate / speed relationship which differs from the average runner, and then it may not really be Firstbeat's fault.

It's highly doubtful that Garmin's implementation of the FB algorithm factors in any kind of drift as evidenced by the Performance Condition on an easy run, long or not. It just takes a nose dive as the run progresses. Interestingly it doesn't when you do some M Pace blocks like I did yesterday, go figure...

Also PC should use HRV in theory, except you also get it with the WHR that doesn't provide HRV...

Honestly it's a mess and they're throwing numbers out there that really don't make much sense and don't get me started on the LT test! Just export your runs automatically to Runalyze and stop worrying about it ;-)

It's highly doubtful that Garmin's implementation of the FB algorithm factors in any kind of drift as evidenced by the Performance Condition on an easy run, long or not. It just takes a nose dive as the run progresses. Interestingly it doesn't when you do some M Pace blocks like I did yesterday, go figure...

Here you seem to assume that HR drift is intended to be factored into Performance Condition. Do you have anything to back up that assumption?

From the observations I described, it would more seem like HR drift is not factored into Performance Condition, but it is factored into the final VO2Max calculation.

Herman,

If, as you mention, cardiovascular drift is well taken into account and as such this kind of fatiugue is then not taken up in VO2max computation, why is then the points you obtain for a long slow run so low, or/and VO2 max for a long run often lower than for a run where you often run slow but still do a few tempo increases?

Hi Steve,

I'm sorry, I don't quite understand your question - but maybe this helps.

1. Your VO2max displayed on your Garmin device doesn't reflect a single run. Rather it is an estimate of your cardiorespiratory fitness (i.e, aerobic performance capacity) provided by a smart analysis of data recorded over your recent training history. Smart analysis, here, refers to an ability to identify and utilize meaningful segments of your performance in the estimate.

2. If by 'points you obtain for a long slow run' you mean the impact those runs have on the accumulation of Training Load and/or Training Effect, then while sometimes confusing, is actually how those metrics are supposed to work. Simply put, there are many, many good reasons to perform long, slow runs - but long, low-intensity performances place significantly less strain on your cardiorespiratory system than vigorous-intensity efforts. It is very probable that a 5k race, or even a HIIT run will have a bigger TE and impact on your TL than a much longer, slower training run.

Hi Herman,

Thanks for the feedback and clarification. I actually do know all of this. I like the firstbeat papers a lot and use insights to share with people I try to train. It is more about judgment of the data probably.

Even considering your two points, I still hold my view - and I am not the only one here on the forum seemingly - that long runs appear not to be valued enough.
It is of course true that long runs at a heart beat of 130 (low aerobic for me) are putting much less strain on you compared to interval and faster runs. My comments is more on the relative valuation eg. with respect to performance load. An example: if i run 18k at 5:30 and heart beat 140 on average I get something like 2.7 points. If I do much less in distance but still at the same speed but now including two very short tempo runs of a minute, then my score goes up markedly. The latter increase is probably inspired by the fact that being in a higher heart zone, one get rewarded heavily for this - rightly so but maybe too much (?) as the time spent in a higher zone was only limited in time given the acceleration of 1 minute.

Another point I want to raise in this respect is that one should not underestimate that with long slow runs people tend do run less efficiently (less tension on muscles etc) as compared to faster runs. In scientific books, there are several ways of computing running efficiency (cadence, vertical oscillation, stride etc...) and somehow this lack in running efficiency at lower speeds needs integrating in eg. figures like training load and vo2 max computations.

I can see why a long run could reduce VO2max, but I dont understand why it would cause training load to reduce.

Yes - I understand that. But its how the training load is calculated that messes this up when it comes to long runs. A shorter hard runs gives a higher training load than a long steady run - despite the impact on the body feeling the opposite. This then results in the watch thinking the load has dropped (short hard run last week, long steady run same day this week), when in fact fatigue has gone up.
It feels to me like there needs to be a consideration for this in the training load calculation.
For example, my 3hr 20.5 miles long run gave 3.4/0.0 on training effect, but a 45 min run at a quicker pace gave 3.7/0.0. But the fatigue I feel was much more from the long run.
How do these numbers then feed into training load ? How are those 'points' calculated ?

Training Load is the sum over the past 7 days of EPOC Peak.
EPOC Peak is accumulated from instantaneous EPOC which is computed from the % of your VO2Max (or % of Maximum Aerobic Speed MAS).

The issue for long run (over 1h30- 2h said) is that you cannot longer achieve you MAS because of EPOC accumulation: so your theoretical MAS / VO2Max should decrease and computed EPOC Peak continue to increase [if your speed is quite constant over long run or slightly decreasing]. This is not the case if you look to detailed EPOC profile of a long run for exemple in Firstbeat Athlete software.
That is why you feel more tired after a long run than a short run despite FB Training Effect are the same.

For longer run, above 6 hours, your heart muscle is tired then you cannot even achieve the HRMax.

Long run is not properly computed in Firstbeat Algorithm : probably the algorithm are based and correlated with measurement on treadmill where the duration is never much above 1h. So next step for Firstbeat would be to introduce some kind of Endurance Index in their algorithm.