Zone 2 Training for an 800m runner looking to do 5k now.

As you don't know your HRmax, training by HR is point and clueless. Forget the
formulas to calculate HRmax, they are all inaccurate.

However, we have your current 5k race time, which is very good. So without knowing your HRmax, you should train by pace. I recommend for you the range of 06:50-8:00 min/mile for easy runs. So what you do at the moment is quiet good.

>08:00 are junk miles for you and you can stay at home and rest instead, would be better.

Please just stop. You keep banging the drum about HRmax.

How many athletes do you coach, by the way? Or have you ever coached?

I am guessing most elite guys train a lot at the bottom of zone 3/top of zone 2. People here like to focus on the 2nd/3rd runs at 7:30+ and ignore the faster moderate run elsewhere in the day. People here quote Nick Willis complaining college kids running too fast but he is running a a lot of 6:30-7:00 miles (i.e. not fast but a long way from the 9+ mins). That 30s slower than the college kids trying to run everything at 6:00 does matter. Just don't go crazy the other way.

Hopefully we start getting elite publish HR data and training logs when they retire. It is one thing to see a week of training. It is another to see 6 months.

I expect if our OP slowed down by a min, nothing would really change. If they want to double training time, running slower will let them do more work.

I have always wished Al Sal explained why he was pushing Mo and Rupp to run 5'40s(call it 90s off 5k pace) instead of like 6:15. He tended to have decent reasons for everything he was doing....

Wouldn't forcing yourself to run extremely slow alter your running mechanics and inculcate bad habits? Why not incorporate some cross training instead?

A number of heart rate by minute means nothing if you don't know your maximum.

And this maximum does not depend on age like you sometimes read, it varies a lot from an individual to another. It is likely you have an high max heart rate, in which case you Z2 is higher than what you think.

That said, being myself a fast twich 800 runner, I runner slower easy pace than people of the same 5-10k level as me. When in 35min 10k fitness I usually jog at 9min per mile, sometimes even slower if tired legs.