[Swizec]

> Is it healthy to run long distances at a constant heartrate vs interval training?

It depends what you consider long distance. Marathons definitely are not healthy. 10ks probably are.

Intervals are great for actually increasing your VO2max without blowing out your cardiovascular system.

Funnily, when you run a raceday marathon, your heartrate (or at least mine) spends most of its time in the 160+ bmp cardio/anaerobic range. You won't be able to do that if your training doesn't involve at limit intervals that increase your cardio capacity.