Debunking “Chronic Cardio:” How Running Keeps you Lean, Fit, and Young

Did you know that some people think running isn’t a good form of exercise – and even that it’s downright dangerous? Are they nuts?!

Chronic Cardio

Recently I got an email from Bhavesh who asked me to comment on Mark Sisson’s post A Case Against Cardio (from a former mileage king). I heartily recommend you read the whole article even if you’re a committed distance runner.

The author runs Mark’s Daily Apple, a health site focusing on a “Primal” lifestyle. The Primal diet is very similar to Paleo and the lifestyle piece also includes aspects of overall wellness and exercise.

My email reply had several points that I’m now going to expand on. But before I start, a short disclaimer:

I love Mark’s Daily Apple. I read it regularly, my wife regularly goes 100% Primal, I own his book The Primal Blueprint, and I agree with about 95% of Mark’s content.

However, I disagree wholeheartedly with his premise that endurance training is counter-productive to good health. Today we’re going to explore some of the science and I’ll offer some specific rebuttals against what Mark has to say. No matter your preference – Primal vs. Endurance – let’s be civil.

Either way we’re all healthier than the average person.

Aerobic vs. Anaerobic and the Intensity Debate

Mark’s argument is almost entirely based on “high intensity aerobic exercise” which he defines as 80-85% of your maximum heart rate. This roughly correlates with just under your tempo pace – or lactate threshold.

Mark claims that runners are doing high intensity running sessions all the time and they:

  • Increase cortisol (a stress hormone)
  • Decreases efficient fat metabolism (so you burn less fat while exercising)
  • Increases systemic inflammation
  • Boring (can’t argue with this one – different strokes for different folks!)
  • Increases oxidative damage (free radical production)

First, let’s recognize that no runner in their right mind would try to do the majority of their running around their tempo pace. If they do, that’s incredibly poor planning or terrible coaching.

For me, that effort would be about 5:40 per mile. In reality, the majority of my running is over a minute per mile slower. And that’s true for most runners out there.

Sounds like “moving frequently at a slow pace” to me.

That pretty much discredits the entire “runners always run at a high intensity level and this is bad” argument since no runner actually does this for all of their training.

But let’s look at Mark’s specific concerns about running.

Running Increases Cortisol

Mark claims that high intensity aerobic training increases cortisol – a stress hormone that can weaken the immune system (and have other adverse health effects if present in large quantities).

This is true – hard running does increase cortisol. But since sane runners don’t even approach their tempo pace for the majority of their runs, this really is a non-issue.

Yes, a very long run or tough workout will increase cortisol levels. But that’s not a bad thing. Cortisol helps the adaptation process; you temporarily decrease your immune system, inflict a small amount of muscle damage, and stress your body. But then, by God, your body adapts and you get stronger!

That’s what training is all about folks. Without a period of over-stress you won’t super-compensate.

Stress Adaptation

Cortisol becomes a problem when it’s released and stays at relatively high levels for long periods of time. As Mark has talked about before, the “flight or fight” stress response from encountering a lion and having to run away is intense but short-lived. The more insidious stress response is the constant, low-level cortisol response from having to work a job you hate for long hours or fighting constantly with your spouse.

From a personal perspective, I was curious about my cortisol level in February of 2010 so I had it checked during a routine physical. My cortisol was perfectly normal and I was running over 60 miles per week at the time – with tough workouts.

As long as you’re managing the recovery aspect of you’re training, hard training shouldn’t increase your cortisol levels to any level you need to be worried about.

Running Decreases Efficient Fat Metabolism

Absolutely not! First, have you ever seen a fast runner? They’re bodies are made thin by thousands of miles of aerobic running that whittle their body fat percentage to the single digits.

Instead of looking at the evidence in plain sight, let’s consider the physiology behind the distance runner’s best friend: the long run.

A favorite among half-marathoners and marathoners, the long run increases endurance (the ability to run fast for long periods of time) by:

  • Increasing muscular endurance – allowing your legs to handle the impact of hours of running
  • Recruiting more fast twitch muscle fibers to share the workload the more fatigued you get (so you actually work on your speed by running long – essentially doing the same thing Mark recommends but through a different mechanism)
  • Training the body to burn a higher percentage of fat instead of glycogen!

One of the main reasons that Mark is against running – it decreases fat metabolism – isn’t supported at all. In fact, this study shows that aerobic training like running burns more visceral and liver fat than resistance training.

And this study shows that running is better than strength sessions for weight loss. This isn’t to show that you have to choose between the two – both have an important part in any healthy exercise program – but aerobic running is actually better for general weight loss.

Running Increases Systemic Inflammation

One of Mark’s major criticisms of running is that it increases “systemic inflammation.” He goes on to say that his…

carbohydrate-fueled high-intensity aerobic lifestyle was promoting a dangerous level of continuous systemic inflammation, was severely suppressing other parts of my immune system and the increased oxidative damage was generally tearing apart my precious muscle and joint tissue.

He has a flair for the dramatic, doesn’t he? My first two gut reactions are:

  1. Mark’s coach had no idea what she was doing.
  2. Mark was severely over-trained.

I just don’t buy that distance running – even high-level marathon training – causes the body to produce a high-level immune response that leads to systemic inflammation.

In fact, Mark posted an article earlier this year that summarized the findings of numerous studies that showed aerobic exercise reduced inflammation (even “high intensity” aerobic exercise). He goes on to say that some inflammation is good because it produces adaptations that are necessary to get “increased stamina…and…improved workload capacity.” Sounds like inflammation is good because it leads to endurance!

His point is that marathoners are “hyper-competitive” and are likely to overdo it. He admits that you can get systemic inflammation from almost any type of exercise if you overdo it.

So in my view, the bottom line is this: over-training is the culprit of systemic inflammation, not simply aerobic exercise or distance running.

In other words: too many hard miles, too many CrossFit AMRAP workouts, or too many sets in the gym are the real enemy here – not running.

Running Increases Oxidative Damage

Oxidative stress is the result of the production of free radicals, which happens during hard training. Strenuous exercise obviously results in more oxidative stress than you experience by going for a leisurely walk.

My issue is that this entire field of study is extremely new and unclear. I just can’t take Mark’s bold claims without an enormous grain of salt. Consider:

  • Oxidative stress is not clearly linked to aging or cell damage (see here)
  • Strenuous running increases free radical production which signals our bodies to produce more antioxidants! (see here and here).
  • Exercise actually protects you from the oxidative damage of pollution (see here).

There’s also a growing body of research that shows supplementing with high doses of antioxidants (like Vitamin C and E) actually inhibit the beneficial adaptations that exercise signals your body to make. So fighting off all oxidative damage isn’t necessarily a good thing

Like I mentioned before, muscle damage, inflammation, and even oxidative stress are all good things provided you recover. So let’s simplify:

Running too much, too hard = way too much oxidative stress = bad

Distance Running: The Fountain of Youth

I’m a firm believer that running is the best form of exercise you can do provided you do it correctly. The impact will help maintain your bone mass while the aerobic nature of running will keep your heart healthy. Coupled with 1-2 weekly, full body strength workouts and your exercise program is just about perfect.

But let’s look at what the science says of the numerous benefits of running:

Whew… Even though I already ran today, I want to go running again!

Running is One Part of Health: Balance and Variety

I’m not saying that running should be your only form of exercise. Of course you know that I love core exercises, strength work, and other forms of cross training like triathlon training.

In fact, all types of strength training are good for your running but heavy lifting is best for your finishing kick at the end of a race (see here).

I’ll also be clear that certain types of running – like racing a marathon – are incredibly stressful. One study compared the level of stress post-marathon to that of military personnel being interrogated or rape victims being treated acutely. But it also shows

“post-race testees did better on tests of ‘implicit memory,’ which is how you store information that you don’t need to access consciously, like how to ride a bike.” It seems that marathon stress “causes you to tap into the older, reptilian part of your brain, where instinct and intuition dominate.”

Sounds pretty Primal to me.

Ultimately, my advice to all runners is to embrace variety and a well-rounded training plan. Not every runner should be doing mega mileage and if you are, keep in mind you’re doing it to optimize performance, not general health.

But the next time a CrossFit, Primal, or Paleo enthusiast tries to tell you that running is bad for you, just smile. You know better.

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  1. Good rebuttals

    • hello I recently gained as a marathon runner and cant seem to shake I have started eating paleo is this a good plan for marathon runners
      and I was told I was under eating body held on ( higher cortisol levels?)

      • Mike Lucas says:

        Paleo is generally a very good plan for losing weight. The only issue is that there are many interpretations of paleo-style eating. I would recommend the book The Perfect Health Diet by Paul Jaminet to clear things up. It goes into details on safe carb sources, how many carbs to eat as an athlete / active person, supplement recommendations etc. And the chapter on weight loss is worth the price of the book alone.

  2. Wow, this was a thoroughly researched response Fitz, nicely done. I don’t have time to dig into all of the studies and I imagine that there are limitations (or outright flaws) in each of them (there always are), but I think that the big point that everyone is missing about the “too much running” study being cited willy-nilly the past week was made by Alex Hutchinson. The study controlled for weight and blood pressure. I.e., if you can maintain a given weight and blood pressure by running a little bit, good for you. But if you can lose more weight (to an extent) by running more, than even better for you.
    So, in essence, what this study does is eliminate two of they main benefits of running and then declare, with alarm, that running a lot isn’t as good for you as we originally thought. I like Alex’s comment where he makes the analogy to height and basketball ability – if everyone were 6′ 10″, then height would have no impact on your ability to play basketball well.

    • Thanks Greg. You’re right – every study has flaws. But the trend is unmistakable: running is good for you. My caveat is that you need to do it responsible ( just like any form of exercise ).

  3. Jason,

    Excellent post. Regarding your point about running most mileage at or above tempo pace, I think this is something that is prevalent among self-guided beginners. You see it all the time on places like reddit/r/running, “I ran 3 5ks this week, and PR’d each time!” Hopefully most people pick up a book or take some good advice before they go too far with this type of routine, and I don’t think it’s a good population upon which to base an argument against running, just thought I’d point it out.

    Your readers who appreciated this post may also be interested in the post on Steve Magness’ site where he talks about Crossfit Endurance.

    • Absolutely, that’s definitely a beginner’s problem. Mark makes the point it’s also a “hyper-competitive marathoner’s” problem as well (i.e., running a lot of your mileage fast). That doesn’t mean running is bad for you, it means too much hard running is bad for you.

      I love Magness’ CF post. It really summarizes why I think the “sport” is bogus: it’s a “non-system of random workouts.”

  4. Steve Wilson says:

    Awesome article. You did an excellent job of explaining it. I know, personally, that I got injured when I started getting back to running mostly because I remembered what I “used” to do. Once I got over myself it all started working out. Thanks again for the post.

  5. Excellent rebuttals. I find it bizarre how Mark states high intensity aerobic training is “popular” and commonplace, and that everyone should try the “new” approach of moderate aerobic training with occasional sprinting. This is already the current training methodology.

    An excellent study everyone should read:

    “Elite endurance athletes perform 80% or more of their training at intensities clearly below their lactate threshold and use high-intensity training surprisingly sparingly … The available evidence suggests that combining large volumes of low-intensity training with careful use of high-intensity interval training throughout the annual training cycle is the best-practice model for development of endurance performance.”

  6. Great article, and I just read Mark’s as well to compare. It was perfect for me to read to learn more about building endurance because I just started using the heart rate monitor that came with my Garmin. I ran my first marathon a few weeks ago, and I’ve been using it to do mostly easy miles based on the easy/recovery heart rate zone. One thing I’ve discovered is that my “easy” pace is a lot slower than I had been doing my easy runs during marathon training. I think one of the main problems I did during training was running my long runs way too fast because my marathon pace ended up being a lot (!) slower than my long runs. It was a good lesson to learn for my next one though!

  7. Interesting timing…I was just in an urgent care Saturday with an injured hand (minor wipe-out in the rain during a run) when a women next to me picked up a local 5k race flyer and said to her friend “Oh this is so neat. I wish I could run. Running is so good for you.” Then her friend replied, “Yeah, well actually it’s not good for you.” and went on to explain why she thought running was bad. I really wanted to cut in to the conversation, but got called in to the exam room and probably wouldn’t have made a great case if they were to ask how my injury occurred! Thanks for arming me with great information for the next time I come across someone criticizing this great sport.

  8. Great article Fitz, well researched and clear counter-points to some of the arguments that Sisson makes. Kudos!

  9. Melissa says:

    Great response Jason! I’m always weary of anyone saying “this is the best that’s the worst” regarding anything. I think we tend to follow fads rather than common sense and listening to our own intuition and how our body works for us.
    I’m wondering also how much of the symptoms Mark talked about had more to do with diet than exercise regime. Perhaps it’s the quality (or lack thereof) of the carbs that people may overconsume when doing more endurance training. From your site you seem to focus more on lean proteins and veg than insulin-spiking white carbs which i think historically used to be the “go to” for distance runners. It seems to me that that would be causing a lot of the excess weight, decrease in immune system etc.

  10. Terrific article! Though there are many research studies which will support any arguement, the most important is to develop a well rounded program for optimum fitness as you mention. Those who have world class rankings and their names in the record books are very few. They have been genetically blessed to withstand the rigors of high intensity over their careers. However, what you have presented is ideal for the remaining 99.99% of us who train and live a healthy lifestyle. Glad to see you have taken the time to present a more positive approach to running outside of the popular training programs we see so much of on the internet. Keep it coming!

  11. I think Mark’s attitude towards cardio comes from his own negative experiences with overtraining, more than anything decidedly evidence based. That is, the en vogue training during his prime was to go as hard as you can, as long as you can, as often as you can. No one, these days, would essentially set up a training plan of nothing but long tempos, whether for an elite or a beginner.

    I think it’s also worth noting that, whether you totally buy the endurance hunting hypothesis or not, humans are indisputably nature’s most prolific bipeds. I can’t imagine we’re so uniquely evolved to cover vast distances on foot if it were bad for us.

    • I agree that Mark’s attitude comes from his own personal experiences, and while I love almost all of his stuff, I have to say that what he’s saying now just isn’t right. Just because he had bad experiences from (maybe) poor training 20-30 years ago – how old is he anyway? – doesn’t mean that he should be posting all these “cardio is the devil” type posts these days.

      But yes, we are truly evolved to run. I love that about us 🙂

  12. Michael says:

    Nice job providing a civil counterpoint, Jason. I did want to point out a nuance in Mark’s point about “Chronic Cardio” that I missed initially. As I read it, his message was not as simple as: “Running is bad; never do it.”

    In “The Primal Blueprint,” he doesn’t even use a runner to illustrate what he means by Chronic Cardio. Rather, he discusses a hypothetical woman who wakes up super-early to go to intense Spinning classes multiple times a week and then rewards herself with a big juice or smoothie afterwards. By doing so, she compromises her sleep (which messes up her metabolism), redlines her HR for extended periods of time (enough to create cortisol issues), and consumes liquid sugar that likely outweighs her “calorie burn” from the workout. Then, she wonders why she is not getting lean. Having suffered through a couple of Spinning classes while recovering from an injury, I found this scenario pretty plausible.

    As for running, I’m sure you’ve heard the saying that most runners run their slow runs too fast and their fast runs too slow. In other words, many runners (including me) often don’t follow your good advice to run most of our miles at an easy, purely aerobic pace; rather, many of us succumb to the pitfall of running every run at a consistent, “somewhat hard” pace, because we have a psychological aversion to running “slow.”

    After all, Mark is not 100% against running. In fact, he recommends that *everyone* do some sprinting (a.k.a. intervals) every week or so. I feel like his “move frequently at a slow pace” recommendation helped me to change my mindset about the rest of my running, so that I was able to stop worrying about the watch and just run at an aerobic pace.

    In other words, I think you and Mark probably would agree more than you disagree, though he may be more cynical than you about the ability of runners to reign themselves in and avoid the Chronic Cardio trap of running too hard, too often. I can’t speak for Mark, but I think he would applaud your efforts to spread the message about smart training.

    • Hey Michael, great points and thanks for that important distinction! Yes, I’m totally on board with that. Like Linda commented, he often blurs the line between general running and intense spinning or over-training. The generalization that I often read on his site that “running is bad” – and so many Paleo / Primal folks die-heartedly believe – is what irks me. It’s ALL about smart training.

  13. Thank you for clearing up the running vs overtraining issue! I’m a fan of Mark Sisson and remember reading that article and thought that is was kinda… blunt. Not as sharp as his usual articles, and I couldn’t get it why running wouldn’t fit his “move frequently at a slow pace” motto as long as you do the majority of your running at an easy pace.

    However, he’s written a (somewhat involuntarily?) post on how to train for a marathon. Which basically suggests you do 2-3 slow runs + 1 interval session + 1 pace run. He states that this type of training doesn’t prepare you for running marathons per se but for burning fat (although he emphasizes the importance of keeping your heartrate down). He’s also written a subsequent post on how to fuel a marathon, where he (again, somewhat involuntarily?) admits the need of carbs. Somewhere around here I started to get why a strict paleo lifestyle is insufficient for runners.

    I think there’s too many contradictions in his posts, or at least he’s not separating “normal” running from overtraining. At least it made me confused for a long time, during which I compromised my health by trying limit carbs. I couldn’t fit running into my paleo lifestyle and since I like running I was unwilling to quit this “chronic cardio”. Which wasn’t a problem once I counting carbs and started fuelling up.

    I’ve read somewhere that there’s no such thing as overtraining, just undereating, and although it’s not 100% fool proof I think there’s something to it.

    • You have to (intelligently) fuel the fire! And you hit the nail on the head about the contradictions he’s made in the past. I’ve read frequently that you can run, as long as you do it correctly, but then read that running is a poor exercise choice. It’s not as simple as that – it’s about doing it correctly. As with any type of exercise, you can overdo it. Great observation Linda, thanks!

  14. Thanks for the great post, Jason!

    As a “chronic” runner myself, I’ve always been amazed at people who make claims about running being bad for you. I’ve found the vast majority of people who make these claims haven’t actually committed much time to the experience of running…and a good deal of them are overweight themselves.

    I’m even more amazed at people who make claims that they know how our “primal ancestors” ate and exercised and that these methods are superior to other forms of training. As far as I’m concerned, it’s like comparing apples to oranges. I don’t live outdoors, nor do I hunt for my food. Give me a blueprint for how to thrive in the 21st century, people…and don’t tell me you’re basing it on something you’ve deduced from scientific examination of 5 corpses that are 1,000 years old. That’s just as irrelevant to me as the diet pill ads on all of the fitness blogs! Show me how YOU got fit…and stay fit. Right here, right now.

    I obviously don’t agree with Mark’s statement that “you must understand how you evolved, then base your exercise program around that blueprint.” However, I feel very empathetic toward his hypothetical woman. I know many of those myself.

    I feel like “chronic cardio” is a misleading term for what is actually happening in this scenario. The situation Mark describes it is actually IGNORANCE. He even makes the statement that it is the “mindset” that has hampered the “nirvana-seeking exercisers” for the last 40 years. Be smart, people. Don’t blame the running.

  15. Jay Novack says:

    Crossfit? Read the white papers to see what is really going on there.–_Timeline.html

  16. Great and detailed article. I think that you bring up some great rebuttals. One thing that both of you mention, in a way, is to pay attention to your own body. Different people at different ages and fitness levels can handle different levels of fitness safely. It seems like it is also important to have a good training program that works for you.

  17. Mike Lucas says:

    Jason, thanks so much for this rebuttal, it really rang true for me! I try to follow the Primal lifestyle and it was actually Mark Sisson’s articles that introduced me to Vibrams, which are what got me started running this year. I ran my first half-marathon in 1:25, and I am totally hooked on running now! Yet the whole time I was training I felt like I was betraying my true beliefs, that because I was doing chronic cardio I wasn’t living as healthy as possible.

    Your article has really put things in perspective. I feel I understand now how running (or any endurance sport) can be part of a healthy primal / paleo lifestyle if done properly. It’s so freeing to understand that overtraining is what can make it ‘chronic’, not the activity itself.

    • My pleasure Mike. Like I mentioned, I read MDA regularly and own his book, I love most of Mark’s stuff. But the “chronic” cardio always bothered me… Good luck with your running and impressive first half!

  18. Good article Fitz.

    It’s also interesting that most studies have shown that endurance training increases antioxidant levels and DNA repair mechanisms — to the point where there’s a decline in DNA damage after Ironman triathlons in well-trained athletes.

    This doesn’t necessarily prove extreme exercise is healthy, but it certainly indicates it’s not less healthy. I went into more detail in this article:

  19. Thanks so much for this post. I’ve enjoyed Sisson’s website, but found the “chronic cardio” phrase a bit troubling. Always appreciate your in-depth thoughtful analysis.

  20. Mike Lucas says:

    A really good book that puts things in perspective in terms of endurance training and health is Phil Maffetone’s “The Big Book of Endurance Training and Racing”. I really like the approach he takes in that health is not always equal to fitness, but by prioritizing health in your training, you will be more successful in the long run. He puts aerobic base building first, aided by very specific heart-rate training to ensure you’re not overtraining. I’ve followed this approach for a few months and found it to be very effective in building mileage and increasing endurance without sacrificing my health.

  21. Great Article Jason! Thank you for writing it!I hear so much from the lifting/strength training fitness community on how running is bad and I am always perplexed as to why they believe that.

  22. Makes sense- but this seems to address die-hard athletes. What about the non-athlete? What about someone who is just trying to maintain good health or go from an unhealthy state to a healthy one, who isn’t training for a marathon- but who hops on a treadmill and spends an hour feeling like they are dying, and suffering as they think they are accomplishing weight loss?


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