Review: Primal Endurance

      48 Comments on Review: Primal Endurance

You’ve pretty much got to like a book when one of the main pieces of advice it offers is to slow down. Of course, that assumes you need to slow down – perhaps not a problem for most of us. If you’re already inert, you’d have to take up cycling or jogging and go too fast before “slow down!” would apply.

But slowing down is exactly what some people need to do. I’ve recounted this story again, but it bears repeating: on one of the low-carb cruises, a woman complained to Fred Hahn that she was overweight despite getting up at the crack of dawn several days per week to go running for an hour. Fred explained that she was exercising too much and sleeping too little. As a result, she was almost certainly cranking out stress hormones, and stress hormones can make us fat.

“But what should I do to lose weight if I don’t go running?” she asked.

“Take a nap!” Fred replied.

I could see the resistance in her expression.  This can’t be right.  Dangit, if you’re willing to wake up at dawn and horsewhip yourself into running for an hour before heading off to a full-time job, there ought to be a reward. It’s only fair.

But our bodies don’t operate on fairness. They operate on biochemistry, and the lack of sleep and chronic over-training were creating a biochemical mess for the devoted runner. Fortunately, she eventually learned the lesson. Several months after the cruise, she wrote a thank-you note on Facebook, telling Fred she adopted his advice and cut back on running to get more sleep … and lost 20 pounds.

Now, I don’t know how many frustrated dieters are out there running too hard and too often. My guess is not very many – partly because so many of us have already been there, done that, and found it didn’t work. While going through some old VHS tapes awhile back, I found one that showed me returning from one of my regular jogging sessions – and I was quite noticeably fat.

My diet was crap in those days (although of course I thought all that whole-grain pasta with low-fat sauce was good for me), so that was certainly a big part of the problem. But I’m also pretty sure I was running myself straight into what Mark Sisson calls the Black Hole in his latest book.

The book is titled Primal Endurance: Escape chronic cardio and carbohydrate dependency and become a fat burning beast! Sisson co-wrote the book with Brad Kearns, who was a champion triathlete back in the day. Sisson, as you probably know, was also a champion runner and triathlete in his youth. Back then, he carb-loaded before races and over-trained. The health problems he experienced as a result prompted him to do the research that led to Mark’s Daily Apple and The Primal Blueprint (still one of the best all-around books on diet and health).

Primal Endurance opens with a nice summary titled 115 Things You Need to Know. It’s essentially most of the advice in the book, boiled down into short paragraphs. The introduction also explains why this book is necessary: too many people trying to get fit are going about it the wrong way, using training methods that are ineffective at best and harmful at worst. In other words, they’re pushing themselves into the Black Hole.

The what? What’s a Black Hole?

Glad you asked. Chapter One is titled Slow Down!, and it explains what the Black Hole is and why you need to avoid it. In a nutshell, the Black Hole is the zone between a proper aerobic workout that burns mostly fat and a high-intensity workout that burns mostly glucose. A brief high-intensity workout is fine – in fact, it’s beneficial. A long aerobic workout is also beneficial. But if you push that aerobic workout too hard and for too long, it’s no longer truly aerobic, and your body has to start cranking out glucose — and to do that, it has to raise your stress hormones. That’s where the trouble begins. To quote from the book:

A chronic approach will lead to poor competitive performance, lingering fatigue, suppressed immune function, persistent stiffness and soreness, increased injury risk, failed weight-loss efforts, and finally – when your fight-or-flight resources become exhausted from chronic stimulation – burnout.

And later:

Metabolically, chronic cardio workouts are slightly too strenuous to emphasize fat as a fuel source, and instead emphasize glucose burning. While this makes the workout more difficult and generates more fatigue and sugar cravings right afterward, the truly damaging effects of chronic workout patterns occur around the clock.

… If your goal is to perform well in endurance events, get leaner, be healthier, and delay the aging process, it’s quite possible that your training sessions are promoting the exact opposite results of your goals.

A lot of us have already heard about the detrimental effects of chronic cardio, so we don’t do cardio workouts at all. No jogging, no aerobics, no Zumba classes, etc. We do slow-burn workouts with weights and let it go at that.

Heh-heh-heh … turns out that’s another one of those beliefs that needs some re-visiting. According to Sisson and Kearns, aerobic exercise is great for health and fitness – in fact, it should form the base of your exercise program – but you have to do it correctly. You have to stay out of the Black Hole. That’s where the “Slow Down!” advice comes in.

Avoiding the Black Hole is actually simple, at least if you have a reliable way of checking your heart rate during exercise. You simply subtract your age from 180 to find your target heart rate. (There are suggestions in the book for adjusting the rate depending on other factors). Then you exercise at a pace that gets you near but not above the target rate.

Sisson and Kearns emphasize several times that you absolutely must monitor your heart rate if you want to avoid the Black Hole. You can’t just rely on how you feel.

You may still feel quite comfortable as you extend your effort well beyond aerobic maximum heart rate. Psychologically, you might even gain a greater sense of satisfaction that you are actually “getting a workout” because of your slightly labored breathing pattern, elevated perspiration, and elevated perceived exertion in the brain…. The black hole has been confirmed by numerous studies as the default landing area for people relying solely upon perceived exertion to govern intensity level.

I can attest to that. Before I even finished the book, I wanted to see what a proper aerobic workout feels like. After some research into various heart monitors, I ended up getting a Fitbit. I like it because if I double-tap the face, it displays my heart rate. (That requires choosing a particular setting in the software interface, by the way.)

So with the Fitbit on my wrist, I got on Chareva’s new bike and began peddling with a fair amount of resistance. A minute or so in, my heart rate was still below 100. Geez, I thought, my legs are working kinda hard here. I don’t know if I can keep this up for 30 minutes.

Then my heart rate began to climb. And climb. And climb. Next thing I knew, it was above 140. I had to slow down, then choose an easier gear with less resistance, then slow down again. I finally found a pace that kept my heart rate right around 120 – and yes, I had to pedal slower than I would have guessed.  Once I settled into the correct zone, it was an easy workout.

So why bother with aerobic workouts at all? The book names several benefits, but perhaps the biggest is triggering the process of building new mitochondria.

Exercise not only increases the size and number of mitochondria, but also makes them more efficient by increasing the number of oxidative enzymes found in mitochondria. These enzymes improve metabolic function of your skeletal muscles, boosting fat and carbohydrate breakdown for fuel, and speeding energy formation from ATP.

To reap all the benefits from proper aerobic exercise, however, we also have to burn the right fuels. Chapter Three is titled The Primal Blueprint Eating Strategy, and if you’ve read any of Sisson’s previous work, you can pretty much guess what kind of diet he recommends.

There are also chapters on adding strength training and sprints to the exercise program, although Sisson and Kearns urge the reader to spend a few weeks building an aerobic base first.

If one of your New Year’s resolutions is to start (or retool) an exercise program, this is an excellent guide to doing it right. Sisson’s books are popular largely because of the solid information he provides, but also because he’s a gifted writer who explains things simply and clearly. Primal Endurance, like his other books, passes what I call my Aunt Martha Test: if you gave a copy to your Aunt Martha, she could read it and understand it all without becoming confused or running for a medical dictionary.

As I explained in my previous post, this book happened to come along right when I decided I need to do more than just lift weights during the winter months. I’ve barely started the program, so I can’t yet say if it’s making a difference. I’ll give it few months and write a follow-up.

I hope the results are very good indeed … because if slowing down is what makes aerobic exercise actually beneficial, that would be welcome news to the millions of people who hop on treadmills in January and give up by April when it’s clear the rewards don’t match the effort.


48 thoughts on “Review: Primal Endurance

  1. Julie D

    Thanks for the review, Tom. My husband and I are just getting back into exercising, and it’s good to know we shouldn’t be killing ourselves to get back into shape. The book sounds like a great resource.

    1. Tom Naughton Post author

      The urge to kill ourselves so it feels like a real workout is exactly what Sisson says to avoid.

      1. JillOz

        Thanks for posting this Tom!

        I never knew what the Big Warning was when I read about over-training. Now thanks to you and Sisson I know it’s about stress, which for me, despite my more prominent medical issues is actually my big issue and always has been.

        That hammock is back on the shopping list. 😉


        1. Tom Naughton Post author

          If you can do low-intensity aerobics in the hammock, it will be perfect. Or just lie there and relax.

  2. mrfreddy

    hmmm, I gave up doing aerobics years ago and never looked back. My only workout these days is a 20 minute HIT (aka slow-burn) weight lifting session out once or twice a week – that seems to give me all the fitness I need. At 59, I can still go out and surf for 4 hours at a go or downhill ski all day. I’ve even put my Pilates loving sisters to shame on the cross-country ski circuit, a highly aerobically demanding effort that I rarely engage in.

    I used to spend hours and hours in the gym and on expensive home equipment. I even had my own starimaster for a few years there. I really like all the free time I found when I dumped the cardio routines, along with all the new space in the apartment when I got rid of the silly equipment.

    But I like Mark Sisson, he’s always a good read, so maybe I’ll take a look and reconsider. Maybe…

    1. Tom Naughton Post author

      My slow-burn workouts with weights put me in the best shape of my adult life. But I figure it can’t hurt to try adding the “slown down” aerobic workouts and see what happens.

    1. Tom Naughton Post author

      Anywhere from 20 minutes to an hour, but it’s important to keep that heart rate in the correct range the whole time.

  3. Ukan

    Just as an FYI, Fitbit are facing a class action law suit due to the alleged inaccuracy of their heart monitor during excercise.

    1. Tom Naughton Post author

      I saw that. I’ve got the latest model, and whenever I check it against the old-school method (feeling my own pulse), it’s spot-on.

    2. Spence

      These personal heart rate monitors use the same technology as the medical ones, granted they are not regularly calibrated or checked and fluctuations can occur. But if people are using them for real medical purposes or depending upon them, then they are foolish. I dont thin any of the manufacturers support people using them this way, its a guide for training and thats all.

      Got to love a law suit over peoples ignorance…..blame the company!

  4. Tuck

    This is basically Phil Maffetone’s approach, which several athletes have used to become world champions. Priscilla Welch used this approach after she stopped smoking, and five years later won the London Marathon, two years after that she became the oldest person to win the NY Marathon, a record which still stands more than two decades later.

    They’ve had Phil on the Primal Endurance podcast a number of times now.

    At the Ancestral Health Symposium in 2012 I met Mark, and asked him about Phil. He mentioned that back in the day he thought Phil was a kook, basically, and thought his approach was ridiculous. “Phil was right”, he then explained.

    Which is what makes me value Sisson’s advice: he’s open-minded and willing to correct himself publicly when wrong.

    I’ve been pursuing this approach for years, and it works incredibly well.

  5. mrfreddy

    I gotta add I read Maffetone and used his methods back in my cardio days. If you just consider changes in weight, it made absolutely no difference when I quit. I went from four or five hour long “slow” workouts a week to zero. My weight stayed the same. I was already low carbing at the time and had basically lost all the weight I was gonna lose, about 40 pounds. Ten years later I’m still at about the same weight, actually a bit lower.

    Anyway, I’m intrigued on what Mark’s justifications are for doing cardio, but I’m skeptical.

  6. Firebird

    I gave up aerobics 8 years ago. I’ve been weightlifting since I was 14. I am now 51. I noticed that throughout my training history, I was my leanest AND strongest when there was no aerobic activity. As a teen I would lift 6X week AND run 3X week. When I have up the running, I put on a lot of muscle and got really strong.

    When the cardio craze came around in the late 80s/early90s, I began using treadmills, stationary bikes, ellipticals, etc. for 40 + minutes per day, 6X week. My weight stayed the same, but my BF% went up. My strength went down, too.

    When I gave up the cardio in ’08, my strength went up again. Even more importantly, my BF% hasn’t wavered one way or the other. I have a small roll of fat on my waist that I’d like to get rid of, but I have to ask myself — having set a personal deadlift record this morning of 440 lbs. (at age 51), do I want to sacrifice my strength and muscle growth by incorporating aerobics back into my training.

    1. Tom Naughton Post author

      I think that’s the experience many people had with cardio. But again, the book explains that the negative effects of cardio are from training in the Black Hole, not from cardio itself. So I figure it’s worth a try.

  7. Mike Jenkins

    One of the things I like about high intensity resistance training is that the gains in strength are documented via the recording of time under load. How will you know if the “cardio” exercise is giving improvements over what was already attained via resistance training? In other words, how do you whether you’ve wasted your time.

    1. Tom Naughton Post author

      Not quite as easy measure as gains in strength, but you’ll know you’re gaining endurance when it takes more effort (faster pace, etc.) to get to your target heart rate.

  8. Angel

    My low intensity aerobic activity is walking. I’ve never liked aerobic exercise classes, but I love walking, especially outside in the morning. I get the triple benefit of fresh air, sunshine (to set that circadian rhythm and keep the eyes sharp) and the aerobic activity. I don’t use a heart monitor though, so I have no idea how far off I am from my target heart rate.

    1. Tom Naughton Post author

      I doubt you’ll exceed the target heart rate by walking. My long night-time walks listening to audiobooks is about the only thing I miss about living in a neighborhood with sidewalks. Walking at night around here could be hazardous.

    2. Firebird

      You are the first person that I have read who said they spend time outside to “keep the eyes sharp”. I have been reading up on Dr. William Bates, an early 20th century eye doctor who was curing people of their vision problems and releasing their need for glasses. He strongly recommended relaxation techniques for the eye muscles, not strengthening them. At the top of his list was a combination of sunlight and palming…placing the palms over the eyes for a bried period of time, then back to sunlight.

      I began wearing glasses in 1999 after years of perfect vision, which I think began in 1996 when I got my first computer. I know correlation does not equal causation, but between that and working in broadcasting for 7 years (at that point), my eyesight went down hill, specifically the left eye and now have a condition called Kerataconus. Bates practitioners say it can be reversed and have observed that people with healthy eyes are people who spend a lot of time in the sun and without sunglasses!

      Keep doing what you’re doing!

      1. Tom Naughton Post author

        I didn’t need glasses until I worked as an editor at the college newspaper and spent hours per day staring at printed copy in addition to my usual reading and studying. I don’t think that’s a coincidence. People who do a lot of close-in work are far more likely to end up wearing glasses.

        1. Firebird

          As we have learned through changes in our diet, the body will heal itself and reverse many illnesses if we 1) give it the proper tools and 2) allow it to happen.

  9. Bret

    “A lot of us have already heard about the detrimental effects of chronic cardio, so we don’t do cardio workouts at all. No jogging, no aerobics, no Zumba classes, etc. We do slow-burn workouts with weights and let it go at that.”

    That’s where I was for quite a while, and I completely lost my ability to run. The Primal Blueprint mentions moving frequently at a slow pace and moving one’s own body weight. I have a feeling this new book will dovetail nicely with that advice.

    Thanks for posting this review. I am going to download and start it today.

    1. Tom Naughton Post author

      I don’t think I’ve lost my ability to run, thanks to the warm-weather farm work. But feeling winded after pulling one load of wood up our back hill was an indication to me that I need something in addition to weight-lifting during cold months. While working on our big spring project last year, I was pulling load after load up that hill.

    2. Firebird

      Dr. Greg Ellis recommended taking one 10 minute walk per hour. For most people that is not practical but he said that taking 6 10- minute walks throughout the day was equal to one long 60 minute walk. I couldn’t do it because it just seemed to burdensome, especially at work.

  10. Joe

    What I would like to know is if there is a good resource out there for Paleo minded folks who also want to compete athletically. If you want to win, you have to train at higher than recommended levels. How do athletes work out at a level that will allow them to compete at the highest levels while mitigating the damage that is done to the body?

  11. Andy

    As I dislike(d) having to spend time exercising I have searched over the past 10 yrs to find programs that requires minimum time and provide good results. I became familiar with HIT protocols, first from Ken Hutchins (original Super Slow), then Fred Hahn and finally Dr. Doug McGuff. I do one of these about every seven days. As for aerobic exercise the information that makes the most sense to me was provided by Dr. Michael Mosley in the BBC documentary ‘The Truth About Exercise’. I use the HIT bike protocol several times a week and that’s enough for me!
    Here’s a YouTube link to the documentary if you wish to watch it. It’s nearly an hour long so maybe you can watch it while you walk/jog on the treadmill if you do that sort of thing! 😉

  12. Nick S

    This is interesting – I picked up a copy and skimmed it a bit. It’s quite good so far, but one big problem persists – I can’t get my heart rate up to the target range, or even close to it, except by one specific exercise, which is sprinting on the ground (not a treadmill.)

    I’m 30, so I should be approaching 150bpm, but I can’t crack 120 except with land sprints. I tried the treadmill and capped out at about 115, tried the rower and capped out at about 120, and the bike is just ridiculous – I have to be FLAT OUT for over 5 minutes to break 110.

    It’s not that these things are not strenuous – I’m no great athlete at the moment! – but my muscles are screaming, I’m setting a rather fast pace (I PR’ed on a 500m row with a 1:38… ~125bpm) and my heart rate is just not rising.

    I’m wondering if I should be concerned…

    1. Tom Naughton Post author

      If it takes that much work to get your heart rate up, you might be better shape than you think. Using the bike, I found that it takes a strenuous pace for the first couple of minutes to get my rate up to 120, but then I have to slow down to stay there.

    2. ion freeman

      I’m not sure what form a medical condition would take that it let you do strenuous activity without raising your heartbeat. Two posibilities are, (a) You’re an android and (b) your heart rate monitor is failing you. My fitbit Blaze works great at rest and gets very very wrong with moderate exercise.

    3. Spence

      You may have a natural low heart rate and blood pressure. I would get a once over by a Dr, see what comes up as well as using a different HR monitor, to rule that out.

  13. Bret

    Tom, at the risk of reptitiveness, I have to thank you yet again for doing this review. I downloaded the ebook and have not been able to put it down. Even though I’m only 40% through it so far, I think it may be the best exercise book I’ve ever read.

    The aerobic endurance advice is making so much sense and just smacking with solid logic, and of course it jives perfectly with eating primally. I’ve trained to run off and on over the years and have always been frustrated by my lack of progress…figured I was just “not born for running.”

    But I started implementing the aerobic max training two days ago (don’t have a fit bit yet, but am combining manual pulse monitoring with exclusive nose breathing) and am already feeling better. Was amazed and overjoyed to finish four miles without being winded or exhausted…even if I had to stop and walk a few times. 🙂 I really do believe I’ll finally make some solid breakthroughs in training here.

    I know I need to share all this at MDA, and I will. But I wanted to let you know, because you are the one who tipped me off to it. Can’t say thanks enough. Cheers!

    1. Tom Naughton Post author

      Thanks, Bret. I believe Sisson is one of the most trustworthy sources out there. He’s a diligent researcher and he’s willing to change his mind when new information comes along.

  14. Willow Wagner

    Wow! Ordering the book. The dogs and I have been power walking uphill and down for about 3-5 miles a day. They’ll be cranky if we have to slow down to a stroll. Well, the sprinter will. The distance kid will just shift gears and keep on truckin’ along. I knew that too much running was stressful, but I never thought about *walking* more slowly.

    Thanks for the review. Yours is one of the most valuable blogs on the internet.

    1. Tom Naughton Post author

      I got swamped with work and haven’t been on the bike enough to give the program a fair trial.

  15. Brad Kearns

    Thanks Tom for taking the time to write such a detailed and thoughtful review. Mark and I really appreciate it. I love reading through the comments and your insightful replies. Thanks everyone on this string for your interest in the book.

    You might be interested in listening to the Primal Endurance Podcast – find on iTunes, stitcher or Libsyn:

    Feel free to ask a question that I can discuss on the Primal Endurance Podcast by visiting

    Good luck everyone with your training and don’t forget to slow down and have fun!

    Brad Kearns
    Primal Endurance co-author

    1. Tom Naughton Post author

      Thanks for the podcast link, and kudos to you and Mark for the well-researched, well-written book.


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