How to maintain 800 pace cause last 300-200 I'm slowing maybe I just need to fight it or maybe I need stronger mental what do u guys think thanks

I’ve heard tempo/threshold long runs are bad. Is this accurate? Because I tapped into threshold today during my 12k long run.

Why am I having such a huge spike in heart rate at 10-11 minutes into my 5k. It’s happened twice now but the effort between before it spikes and after feels the same. Is it that I’m hitting the lactate curve? Or is there another reason?

Is there any way to keep building/maintaining aerobic base while sick?

Hi guys I'm wondering what is the best weekly plan. Is it better to stick on 1week training plan then repeat or is there any best way than this like 3 week fast and 1 week recovery btw I'm 15 year old and 5k is 21mins what's the best for me I have track meet in October thanks.