A lot of people in the paleo world think that jogging is "chronic cardio." According to them, cardio exercise causes you to raise cortisol levels, increase oxidative damage, systemic inflammation, depress the immune system and decrease fat metabolism.
The trouble with believing this is that I spent the last 9 months doing the kind of exercise paleos advocate and I ended up feeling that I was getting all those negative things. Since paleo is all about looking to the paleolithic for how we might best eat healthy and exercise, how did anybody come to think it's natural for humans to do burpees and planks and avoid running?
What I really found enlightening about Maffetone's Big Book of Health and Fitness was that he explained "chronic cardio" not with blanket statements about some exercises being better than others but in concrete terms that overtraining is bad. Overtraining leads you to raise cortisol levels, increase oxidative damage, systemic
inflammation, depress the immune system and decrease fat metabolism. And you can overtrain doing burpees and planks, lifting heavy and sprinting like paleos say is best. You can also over train by running and biking if you push too hard.
I continue to run slowly most days, ride my bike slowly and generally not work quite so hard, yet I put in the time. I feel happy and healthy when I do it this way. The 9 months I spent doing twice weekly burpees and the like was just too much. Always hiking at high speed was too much. Always pushing hard when I rode my bike was too much. Easing up is so much better.