Just to comment on this. I doubt that is true.

I was a distance runner from 15 to 30 years of age. I averaged 70 miles per week, running every day, typically 7 min/mile. As I got older, I ran marathons. My typical LSD (Long Slow Distance) were 18 mile runs. And I raced often -- mostly 10K and up.

I know of no distance runners whose health deteriorated while running.

I know you can over train -- for me, 90 miles per week just was too much stress. I also did HIIT training -- 20 1/4mile sprints with 1-2minutes jog/walk/crawl recoveries between each one. That type of workout was too intense/too stressful to do more than one a week (at least for me).


I would suggest that most people do not do any where near that level of training and therefore are not reaching the level of over doing their cardo workouts.