https://www.menshealth.com/uk/fitness/cardio-exercise/a69053608/average-5k-time-for-men-training-tips/

Rossner cites some research where a group of researchers wanted to find out if you train less, can you still run a faster 5k? ‘So, they took a bunch of runners who were already running an average of 30k per week, and then they cut their training by more than half,’ he says. ‘So now they just ran 14k per week. That’s barely over 8 miles.

‘Their average 5k time dropped by 48 seconds in just seven weeks. All that with less than half of the training they were used to.’

To replicate this, the programme would be as follows, three times per week: 

• 10-minute warm-up.
• 5 rounds of 30 seconds easy, 20 seconds medium, and 10 seconds hard (5 minutes).
• 2-minute rest.
• Another round of 5 minutes. 
• Repeat those rounds 3-4 times.