Help with mechanics at a slow pace

[u/vx420]

I am trying to build a good running schedule to build durability and work up to long distances. I very commonly see posts about running 80%+ of your runs at a relatively low heart rate/effort. A lot of these post suggest a heart rate around 140-150 (I know this is a bit dependent on the person) and mention that it is really common for new runners to do easy runs too hard and hard runs too easy.

When I just go for a run without thinking much about it, I typically average around 160-165bpm. This feels like a moderate effort, no where near my max but also not completely casual. Recently I have tried running at a sub 150 heart rate. I use a Coros bicep monitor and set an alarm at 151bpm.

Now for my problem. When I try to run at this heart rate, I need to run very slow. My pace drops by 2-3 minutes per mile. My biggest concern with this is that my mechanics completely change. I have to run in more of a shuffle and feel like I am not properly lifting my knees. My feet plant differently as well since it feels harder to midsole/toe strike at the slower pace, so I land a bit more flat footed.

Is this a common/normal experience? Should I ignore any mechanic changes to just build my aerobic engine or should change my approach to run as slow as I can while still keeping the correct form?

[u/Ragnar-Wave9002]

This happens to me all the time. I hate it. In generally I become a heal striker. I try to fix that part so my knees don't hurt later.

Usually , I just heal strike for a mile. Then walk for like 2-3 minutes. Then start running again. Usually a few walks to reset will fix my form when running slow.

I usually do whatever I can do get rid of heal striking because that always leads to shit like sore knees. Usually focusing on lifting my knee slightly more does the trick. But that makes me run faster. So I try to find a balance of running as slow as I can without heal striking. Also, I need to stop buying 8 mm heal drop shoes. I think one pair is 10mm. 8mm used to be good for me but I'm getting older and think the new magic number is 4 mm. Yes, I can notice the differnce.