Trying to understand an unusually low Load Score

At glance you sure seem to be on to something likely with how Trail Run vs Run is calculated.   You'd definitely think that an 81min Run @146bpm avg would be much higher impact to load than a 55min@143bpm.  I would say that the only thing I can think of is that your HR in the regular shorter run was erratic and hit some higher zones (by sensor error by actual).?  Maybe got some time in higher zones although having a generally low HR?

   Another possible long shot is that it somehow takes into account previous days training?  If recent load is super high it possibly gives subsequent training more 'Load' due to performing on tired legs?  lol    For example... if I do an hour run aerobic each day (load of 80), but one day, I decide to do a hard bike workout (load 150) for an hour right before my hour run.  I do the same aerobic run... should it really by still a load of 80?  (lets ignore that likely my HR would be a bit higher due to heat/fatigue)    Now instead of coming into run with a recovery time of ~zero.... you are coming into your activity with a recovery time of ~40hrs maybe.   

Curious did you maybe have some good workouts the days leading up to your 4/19 regular 55min run?  And/or did your 'Performance Condition' read a bit negative for the 4/19 run ?

Sharing links or screenshots of the activity data can be very helpful.

Good points on how prior days' loads might have an effect, I hadn't thought of that.  I know both days were immediately preceded by a 30-40min bike but the bike before the 4/19 run was slightly higher in Intensity - so that could be a factor.  Let me see if I can spot anything in Performance Condition that might provide a clue.

4/19 Performance Condition:

4/23 performance Condition:

So clearly the 4/23 run had a much "poorer" Performance Condition score, but why would that contribute to a lower load?  Seems like Load should be higher in that situation.

I guess I can't think of why that would be the case, does seem a bit backwards of what 'could be effecting it' .   Most likely that HRV and Performance Condition doesn't play into the Load/TrainingEff calc. 

Agreed.  I will say that the 4/19 Run has a very typical "load" for this run.  It's a group run I do every Tuesday, usually the same distance/route and the Load is usually pretty close.  It's the 4/23 Run that has the unusually low Load Score, especially compared to others.  

I had a similarly unusually-low score back on 4/9 on this same course, but that one had a much lower HR avg (131) and slower pace - hence why I was surprised this 4/23 also came in pretty low.

i just had a ride that scored unusually low

That's curious and a good question because I did pause this run a few times (I run with my dogs and I stop at creeks for them to quickly cool off and drink) but never more than 30sec.

For cycling it's very clear that Garmin uses Power to accurately calculate Load, but for Running it's some cryptic combination of HR and (I think) Pace.  Maybe HRV is factored in there too.  That recipe feeds EPOC or what they call Load.

But what you're describing are the Aerobic/Anaerobic "Training Effect" which is a different measurement from Load.

right sorry. it's 216 vs 0 on the two rides. surely riding at 200+ watts for nearly two hours should count for something. i looked around and it is showing the load on the training status card. the various charts and bars they have in there does show a 400+ load on today's ride. maybe you can see how your two runs compare on there on the exercise load tab (im not sure if that's what it's called since i use it in a different language)

Certainly a Load of 216 for one (easier) ride and 0 for the harder ride means something is amiss.  I get a load of 5-6 from just a 1m easy walk!