I used to be a hard runner for about 25 years, always running to music playlists that evolved over time. I would challenge myself based on my vibe for each run, telling myself to go full out for the next chorus, or guitar solo, etc. Further into my playlist, when I knew I'd be well warmed up, and at my peak, I would put 3 or 4 higher intensity songs in a row, followed by a rest song that still kept up a decent pace. It worked great for me.

Years later, after I'd gotten away from running and gained quite a bit of weight, I'd get skeptical looks at cardiac workups when I said I used to run. Then they'd run the tests and say "You should start running again, you're heart is fine." One cardiologist even said that all that hard running when I was young is still paying dividends DECADES later.

The guy who was my running mentor when I was young said "Running is the King of exercise."