My brother and a fare better runner than I ran a 5k race today. Time was 16.53.
I asked him to summarize his training.
He is using a typical polarized approach.
In 2016 he ran 179 times.
189 h of training.
Interval training 1 time a week, typical 1000m intervals or 5x6m, all with short rest.
All other runs were in zone 1/2.
Typical HR 118-125, never more than 130.