Unable to get a good Execution Score for a VO2 Max Workout

never ever tried Garmin's VO2 Max workout, but here are some reasons why you cannot reach the target HR

1. invalid max HR: your real max HR is not 169. Garmin is notorious to show values that has nothing to do with the reality. if you don't reach you near max HR at longer max efforts usually, then there is a high chance that your real max HR is lower, it is just garmin once in a while hallucinated an unrealistically high HR.

2. lack of proper nutrition / overtrained state / lack of sleep / underlying illness: if you are not in an optimal state, you may not be able to reach you HR targets, no matter how you are trying

3. your central capacity is higher than your peripheral capacity: if you usually do different type of sports (swimming, cycling) then it is possible that your heart is actually more capable than your running muscles require. in this case, your cardiovascular system will be underloaded regardless your effort

3.b you are detrained: this is a variant of 3., your cardiovascular fitness detrains at a slower pace than your neuromuscular system, so if you skip 2 weeks of running, then your neural paths can weaken to that extent that it won't be able to drive your muscles

I think these are all possible, and knowing your usual capabilities, it could help you to pinpoint the actual issue(s)  

A heart rate strap is essential for these types of workouts if you want to get a good score as there is too much lag using the wrist HRM. 100% is possible - i've done it.  Also your lactate threshold and max heart rate need to be set correctly in the first place otherwise it becomes too difficult to achieve the suggested targets.  There are a lot of complaints about the current algorithims being use to calculate lactate threshold automatically so do not blindly rely on what the watch calculates.  From the information you have given it seems that this may be the case

I appreciate your suggestion to use the chest strap and will try it soon.

I think that the lactate threshold that was set by the watch is accurate based on two pieces of evidence.

• The auto-detected lactate threshold of 154 is 91% of the auto-detected maximum heart rate. This would put these numbers in line with the ratio of what I've seen is true for a very fit person. Specifically, that very fit people have LT that is about 90% of MHR and that less fit people have ratios down into the 80s.

• While I can run for some time at just below LT, I quickly run out of the ability to sustain much effort over my LT of 154. This would seem to indicate that the LT detected by the 965 is correct.

I see any adjustment to these numbers as gaming the watch in order to be able to say that I can run at rates above LT or at MHR.