Regarding the recent discussions on threshold training, let me save you a whole lot of pain and frustration...
The following chart from chapter 11 of
#TheEnduranceCode tells you everything you need to know 👇
"You can become good with a focus on threshold training. But without a deep aerobic base to go along with it, you will stay (just) 'good' for a very long time!"
If you want to discover your potential as an endurance athlete, Aerobic Base work is the (only) gift that keeps on giving.