Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
9 Jul

The Evidence Continues to Mount Against Chronic Cardio

marathonrunnersIt’s been awhile since I did a post on chronic cardio. I had a good string of them going several years ago, and I thought I’d done a good job explaining why I was so opposed to excessive endurance training. Despite my attempts to clarify, though, I still receive a lot of questions and comments about cardio. People just have a tough time divorcing themselves from the notion that cardio – as much as you can cram into your schedule – is the key to health and fitness. I don’t blame them, really. It’s conventional wisdom, after all, and it’s what I thought for years and years. Clearly, another post is needed.

Evidence against chronic cardio continues to mount, so there’s a lot to cover. But before we get to all the research, I have a few thoughts about the heart.

Here’s the thing about the heart: being an involuntary muscle, it has no say in the matter. It pretty much feels nothing, too. It’s along for the ride. Just like the liver, kidneys, pancreas, thyroid, adrenals, etc., the heart responds to biochemical signals. It’s a demand organ. Minor changes in blood chemistry (epinephrine, cortisol, insulin, lactic acid, hemoglobin-depleted RBC’s, to name a few) cause it to respond by beating faster or slower, forcefully or not, to keep pace with the muscles’ (and other organs’) demand for oxygen and fuel. During exercise, it’s the brain that starts this whole process with a (usually) conscious decision: “I think I’ll run to that tree.” That thought prompts the muscles of the legs to start moving faster and the arms to pump. The new, increased demand for oxygen and added fuel (over and above normal resting metabolism) signals the heart to start to fulfill the demand, to pump harder and faster. It’s obliged to do so. Period. No choice. That’s also why it’s always a bit behind schedule: it takes more than a few seconds to ramp itself up once the action begins and a few seconds or minutes (or hours, in the case of an over-trainer) to ramp down, once it’s over.

The problem with chronic cardio is that we can force our brains to override some of the tiredness (no pain, no gain, pal) and discomfort in the legs – and to a certain extent even the lungs – and keep doing these hard endurance workouts incessantly day in and day out. The ostensible limiting factor is the ability to burn fat or, at the very least, the amount of glycogen still left in our muscles. That’s what eventually brings us to a halt, frequently because we have willed ourselves to keep going through the wall at all costs. But the heart is often over-worked in this scenario, just trying to keep up with that “inhuman” (and inhumane) desire to run, cycle, or swim further and faster in pursuit of…what? A medal? A ribbon? Bragging rights? It can’t say no. It attempts to do as we bid it. And because the heart feels little-to-no pain – unless, perhaps, it feels the REAL pain of a heart attack – it very often suffers silently as a result without us ever knowing. The walls of the heart start to hypertrophy over time the same way a biceps muscle does when you do curls. But do a few too many curls and your biceps will get sore quickly. Force yourself to do a few more and you could even tear something and be out of contention for a few weeks. We know when to stop before that bicep tears.

Cardiac muscle doesn’t tear that way when over-worked, but it does enlarge and thicken with chronic overuse. In some – most – people the thickening is probably not life-threatening, but in some cases, as with dozens of world class athletes I have personally known, this thickening can cause all manner of issues later in life. Atrial fibrillation has become a mild epidemic in my generation of life-long aerobicizers; several of my friends have had pacemakers or defibrillators implanted before the age of 40 to head-off those sporadic life-threatening cardiac enervation problems. A few more friends have lost significant cardiac function and a few have died.

But don’t take my word for it. The silent epidemic of heart issues among endurance athletes is getting serious attention in the research community. Let’s take a look at some of the latest research.

Cardiac Arrhythmias

Cardiac arrhythmias are abnormal electric activities of the heart. An arrhythmia can describe a heart that beats too fast, too slowly, too irregularly, or too “fluttery.” An arrhythmia doesn’t always indicate or foretell heart trouble, but it’s a common risk factor. One of the more common varieties is atrial fibrillation (AF), which describes a fast, irregular heartbeat. AF is strongly linked to stroke and cognitive decline.

Endurance athletes are at a greater risk for atrial fibrillations than the general, non-running public. One recent study of cross country skiers even found that the best athletes, the top performers, were more likely to have cardiac arrhythmias than the rest. Moderate exercisers, meanwhile, are at a lower risk for AF than the general, non-running public. A recent comprehensive study offers several potential explanations for the increased risk:

  • Increased fibrosis (scar tissue formation) in the heart.
  • Myocardial injury to the heart, as evidenced by post-training elevated cardiac biomarkers typically used to diagnose injury. Probably not a big deal so long as you recover fully from your training, but most cardio junkies can’t wait that long to log more miles.
  • Excessive amounts of inflammatory markers brought on by training. These markers have been linked to AF.

Endurance-related AF usually starts off infrequent. The older you get and the more miles you log, the more entrenched and regular your atrial fibrillation may get. Some studies found that around 40% of athletes with AF eventually progress to persistent AF, where it’s happening on a regular basis. That’s the troubling kind of AF that may presage serious cardiovascular problems, like stroke.

Atherosclerosis

It’s totally counterintuitive to think that endurance athletes are at risk for arterial plaque. “You mean to tell me that the wispy greybeard whizzing past my house in short shorts every evening could have clogged arteries? No way.” Maybe, just maybe.

A 2011 study found evidence of carotid and peripheral atherosclerosis in a group of marathoners. Although there was no control group of non-runners in that study, another study compared the arteries of marathon runners to a control group of sedentary non-marathoners. Marathoners had more calcified plaque in their coronary arteries, which has been linked to stroke and dementia. The tricky thing about these cases is that endurance athletes with atherosclerosis don’t evince the regular signs. Whereas your typical sedentary guy with extensive atherosclerosis will probably have all the hallmarks (metabolic syndrome, abdominal obesity, hypertension, etc.), marathon runners with atherosclerosis don’t fit the traditional cardiovascular risk profile.

It might be time to add “trains for endurance athletics” to the list of risk factors.

Oxidative Stress/Overtraining

It’s no secret that endurance training induces oxidative stress on the athlete. That’s how we get better – by encountering a stressor, being broken down a bit, and then recovering stronger than before so that the next time we encounter the stressor, we’ll be better than the last time. Whether we’re talking strength training, marathon running, cycling, gymnastics, martial arts, or even studying for a trigonometry class, we have to challenge our physiology to get better, and challenges to the physiology mean oxidative stress. Problems arise when we don’t let up, when we keep the intensity elevated and the days off few and far between. We’re constantly in that post-workout state, and it starts to look like chronic oxidative stress for all intents and purposes. Even if our times are improving, we’re not truly recovering. It’s a two steps forward, one step back kind of thing.

So. Those are just a few of the reasons I am no fan of chronic cardio (and don’t get me started on the bad backs, osteoarthritis, hip and knee replacements and chronic tendonitis among my former elite endurance peers). A strong will can be a great thing for survival, for business and for relationships, but it can also get you in trouble if you don’t pay attention to your training load.

Having said all that, I am still a big fan of weights, of brief, intermittent interval training and I am all for doing a fair amount of mixed low-level cardio, the kind that doesn’t overstress the heart or involve so much repetitive joint motion that it causes chronic injury. That makes sense in an ancestral context. You’re expending energy at a high rate, but you’re not going long enough that it becomes a liability. Or, if you’re going long, you’re taking it easy enough that you have the energy to make it back home, possibly carrying food.

I’m not even against a long training run or ride once in a while, provided you are trained, rested and allow enough recovery afterwards. I’m even OK with running marathons occasionally or jumping into a short triathlon now and then. As a species, we obviously have the capacity to go long and relatively hard every now and again. It’s the chronic, day-in, day-out long, hard stuff that is counter-productive. If you did that twenty thousand years ago, when your next meal – and that of your entire family/tribe – was on the line, when calories were somewhat precious, when you didn’t have an air-conditioned caravan of trainers, massage therapists, and coolers filled with electrolyte drinks following along after you, you’d be foolish. You simply wouldn’t do it.

That we can run marathons (and do other stupid things) and know that we’ll get out alive is a luxury of modern living. There are so many other less damaging ways to achieve what I would call high-level adaptive fitness by using a variety of training methods, all of which can be cardio-protective and joint strengthening when done the right way in at the appropriate times. Heck, when it comes to hypertension, blood lipids, and type 2 diabetes, walking is just as effective as running – without the potential downsides. Everyone can walk. Everyone thinks they can run, but running is a skill that must be learned. To run with poor form is to welcome injury, doubly so if you’re running an excessive amount. And all this will be addressed in detail in my forthcoming book, Primal Endurance. For now, use your brain and listen to your body.

My point, of course, is that the human organism is made for short, intense bursts of activity laid atop a foundation of frequent slow moving. We aren’t “supposed” to run as hard as we can for two or three hours. We’re not supposed to run with the express purpose of “burning calories.” We can certainly choose to do those activities, and we’ll become adapted (or perhaps inured) to them, and they may even make us “fit,” but they’re not the healthiest, most efficient path to fitness. Chronic cardio is the meandering, roundabout trail that will get you there with a ton of bruises, scratches, a tick or two, and a sprained ankle. Oh, and you might get eaten by a bear along the way.

Your choice.

Thanks for reading, folks. I’d love to hear your thoughts on cardio, both chronic and otherwise. Let me know in the comment section!

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. Hi.
    I’m 50.
    I do competitive road cycling. I’ve been doing it on and off since I was 17. For most of the 90s I did 10k running races along with 1/2 marathons.
    I was a Vegetarian for 17 years until I changed to being Vegan 2 /12 years ago.

    I have no joint problems.

    I ride & cycle race with men and women whose ages range from 17 to mid 80s. They’re still doing what they’ve been doing for years, decades even.

    Compare this to what we read, hear and see in the news with regards nations populace of diseased, overweight and immobile people.

    For the very few who suffer joints or heart problems the many who major on cardio exercise benefit greatly from it.

    Paul ;-)

    Paul wrote on July 11th, 2013
  2. I’m going to play devil’s advocate (I live primally, and it works great).
    What about the Tarahumara Indians? They eat a high carb diet, and do lots of cardio. And they live to ripe old age without heart, weight or joint problems. Why?

    David Franklin wrote on July 11th, 2013
  3. Never liked long cardio sessions, just hated how my lungs and wind pipe would feel after 5 minutes of constant running, it just didnt feel right, on the other hand HIIT was always much more fun, particularly the resting bit! haha

    Goran wrote on July 11th, 2013
  4. I love Mark’s posts about chronic cardio because the discussions in the comments section are amazing, passionate, and thought-provoking. Chronic cardio means so many different things to different people, so here’s ***My Two Cents***

    When I was in college and tried vegan and chronic cardio, I gained weight. When I say chronic cardio, I mean hopping on the treadmill every day come hell or high water and trying to keep going for an hour. It sucked. I got injured. I also gained five pounds super-fast.

    I added meat back into my diet (I think vegan lasted all of two months, max), started doing typical body-building split weight training, and every other day would pedal on a stationary bike at whatever pace I felt like for an hour while I read whatever guilty-pleasure magazine I felt like. It was “me time.” I lost all the weight I gained during my vegan/chronic phase.

    Note: I was still doing an hour of stationary biking a day, but I was not aiming for a heart rate and I was not aiming for a pace; I was aiming to be active while I read a favorite magazine. Total pleasure.

    A couple years later, I discovered Paleo, followed soon by Primal. I kept up my alternating weights/slow cardio, changed my diet, and honestly lost too much weight.

    Then I read that chronic cardio is bad for you, heavy lifting is good for you, lift big, eat big, do sprints. I gained weight. I also gained sluggishness. Sprinting only helps my time trials to a point, and then I actually have to DO the time trials. I don’t have to do a million long, slow runs to jump into an endurance event, but if I make my long, slow runs truly SLOW, I feel good, I maintain my weight better, and whatever event I want to partake in goes well. It’s still not chronic because I’m not pushing myself through any pain barrier, and I’m definitely falling into that 10-11 minute mile pace for the slow stuff.

    So, for me, I need a combination of weight training, sprinting, and some long, slow cardio (that is more difficult than walking — walking isn’t enough) to maintain my weight and my preferred level of fitness.

    A note on endurance events: they do not have to be “chronic.” I ran a half-marathon with a friend last fall, and my job was to get him to cross the finish line. He was eventually going so slow that I would run ahead a few yards, stop, cheer him on to keep going, and then when he caught up, I would run ahead, wait, cheer, run, wait, cheer… Nothing chronic about that.

    That’s my take on that. Fitness is definitely as individual as diet. One size doesn’t fit all.

    Deanna wrote on July 11th, 2013
  5. I am a little confused. I understand the sprinting part. But I don’t understand the rest. Is riding a bicycle for a long ride bad? Does it count as chronic cardio? If I walk on the treadmill for an hour, is this “chronic cardio?” How do you draw the line to what is “chronic cardio” that is not good for your body, and what is just doing long sessions of exercise that are good for you and not considered “chronic cardio?”

    Brian Smith wrote on July 11th, 2013
  6. I wonder if symptoms related to this were what got Bruce Lee. He trained endlessly…

    Ian Connel wrote on July 11th, 2013
    • Pretty sure it has some sort of brain thing not the heart.

      Mark wrote on July 11th, 2013
  7. First of all, in the book “born to run”, McDougall says we are evolved to run. Running is uber-paleo because endurance running is why we are bipedal and have sweat glands all over our body and not hairy like monkeys. It was to do a form of hunting called persistence hunting. We had a tremendous evolutionary advantage over other animals because other animals cannot do endurance cardio and quickly overheat when they try.

    After that, if you recommend weight training, then why don’t we look at the health problems of professional bodybuilders or powerlifters? If we are going to look at professional endurance athletes’ health problems, then it’s only fair to compare them to bodybuilders.

    Yes, weight training can make you leaner (in terms of body fat percentage) but is carrying around 25lbs of muscle better than not carrying around that 25lbs of muscle? If we have extra muscles, our heart has to work harder to supply them with blood and so, over the long term might cause problems. Our body naturally destroys the muscles we don’t use and grow the ones we do and so, why would we want to grow muscles for the sole sake of growing them. By doing weight training, we are essentially hacking the body’s system of allocating resources to growing muscle to adapt to the environment.

    Couldn’t it be that the heart diseases are more linked with diet than with use. Maybe endurance athletes guzzle gatorade and their diet is pizza and beer that causes the heart problems. After all, endurance athletes are marketed a different way than regular people.

    Anyway, this isn’t something that can just be thought of on paper and figured out. Yes, endurance training can cause various forms of stress on the heart muscles but how significant is that that stress to the long term health? Maybe its just a few athletes who are training incorrectly that are having problems.

    Mark wrote on July 11th, 2013
    • That’s so true! People die weightlifing, but maybe that is because of all the artificial milks and foods they eat, supplements, sleep habits, etc. There is a middle ground for all types of fitness training, and applying great nutrition serves to enhance its health benefits.

      lisa wrote on July 12th, 2013
  8. I think I once had a heart attack or something similar… it felt like my heart stopped beating for maybe 5 seconds or a bit more; then for about a week after I had an ache in my chest. This was caused by a reckless dose of recreational drugs. I still drank an energy drink or two every day after – oh, I can take it! (well, guess I could, since I recovered fine, but I bet I could have cut that time to half if I didn’t keep drinking Rockstars and Monsters (hey, I wanted to work fast cleaning garbage up so I could get a headstart on my homework or just chill out in the cafeteria and chug 25 cent small styrofoam cup coffees with as much sugar as the machine would pump out from pressing the button like an uzi and a muffine too! and teas in the factory cafeteria so I could read the newspapers from the floor or laze around or hide smoking weed in the change room or janitor closet or smoking area outside).

    Animarchy wrote on July 11th, 2013
  9. What is chonic cardio? I have always hated running but was challenged to do a 5K. I started a couch to 5 k program. I discovered real quick that I hate the road running. I decided to go off road.I did do the 5k and ran the whole thing.

    Found that I really like trail running on hiking paths I have come across deer, moose, rabbit and all kinds of brush dwelling birds scaring the daylights out of me when they take flight. It has become a zen-like experience. I go at an easy pace. Is 1 to 3 miles a day, 2 or 3 times a week considered chonic? Should I scale back to once a week and walk the rest?

    patty pittman wrote on July 11th, 2013
    • Less than 6mile per day isn’t considered chronic from a previous article. Plus, if you’re going at easy pace, it probably doesn’t even register.

      Mark wrote on July 13th, 2013
  10. Dear Mark,

    I’m a amateur bike racer who trains 8-12 hrs a week. And a little different than many chronic cardionistas –I only race 2-3 times per month, mostly short races, and I only race about 3 months a year.

    My only other exercise is walking, and I walk around 2 miles a day on errands and such. Oh, and I do a little plyometric activity to keep my hips limber and strong –compensating for the nearly one-dimensional movement in cycling.

    Since my longest races are about 3hrs, my training is set accordingly, broadly speaking, I do about two 3 hour rides per week at low-to-moderate intensity. I rest well for a day or two following these longer rides, sometimes with an hour of light spinning on a rest day, sometimes no riding. I throw in one more intense, but shorter ride per week. Some sprint work gets added here and there, but it’s minimal.

    I feel good and my blood tests look great. My diet still contains spikes of sugary stuff and some unplanned grains (pastry and beer), but most of my intake is high-quality primal.

    I feel good physically and mentally, sleep well at ~8hrs a night, spend lots of time in a relaxed, contemplative state of mind.

    Altogether I feel like I felt when I was a kid –the duration and intensity of play is very similar to my childhood days. Of course there was more impact with wrestling my brothers, climbing and jumping from trees, etc. decades ago. And I’d like to bring more of the latter, resistance/strength play, into my life now –so I’ll probably add some weightlifting in the near future.

    But with my current training load, which stays more or less constant throughout the year (with week long breaks 3-4 times/year for extra rest), my stress/rest balance feels right. And it wasn’t until I began this kind of training that my heart arrhythmia disappeared.

    I don’t think the bike is the best sport/exercise for the human body, but –for me– it brings an amount of sheer fun and joy that nothing else can match.

    Thanks for all your informative and enjoyable writing.

    Norm wrote on July 12th, 2013
  11. When I was a child my dad told me that “You can’t believe 99% of what you see on television and 97% of what you hear.” Boy-o-boy, was he ever right! We are constantly bombarded with all kinds of commercials on television and adds in magazines that promote all kinds of diet and nutrition advice, exercise advice, medical advise, etc. And I have come to learn that the vast majority of all this advice is the exact opposite of what the truth is! The vast majority of it, if followed is destroying peoples lives and even killing people prematurely. I have come to learn that what ever is promoted… AVOID IT or DO THE OPPOSITE! According to the “oh-so-wise” talking heads, we are supposed to eat lots of grains (and then we wonder why people are obese and have all kinds of intestinal problems), avoid eating whole eggs, meats and dairy products (because they are bad for your heart) but eat their man-made replacement crap which will plug up your arteries and heart tighter than a pipe packed full of cement, drink their man-made/processed sugars (which cause FAT gain and brain problems, etc), pop this pill and that pill (which causes other problems requiring treatment with another pill) that we see advertised every 15 minutes on tv, run our a**es off since we mostly hear about or see people doing this, etc. Finally, the truth is starting to come out about all these lies because of sites like this one. I’ve already read several articles over the past few months prior to this one, that through research studies show that looong-boring cardio will make you fat due to muscle-loss and destroy your heart. My advice to people if they want to live a long healthy life, is to eat whole, unprocessed foods like our grand-parents and great-grand-parents did and avoid the processed garbage. Additionally, if you want to look weak and emaciated then run you a** off like a marathon runner. Personally, I want to look like a muscular, yet lean and well-defined or “ripped” sprinter. Short, yet intense exercise such as Metabolic Resistance Training (MRT), Metabolic Conditioning Training (MCT), and High Intensity Training (HIT, not HIIT, that’s High Intensity Interval Training) done NO MORE than 3x weekly, will perform wonders. One can use one of or even better a combination of these programs. The problem is people tend to OVER train. As you become stronger the rest periods and workout frequencies need to be extended to avoid adverse affects. People would do themselves a tremendous favor if they’d learn to ignore the vast majority of what bombards their minds daily. They’d also have more money in their wallets… after-all, that’s what these companies promoting this “garbage” are after anyways! Make the food and exercise industry rich by eating their garage and buying into every gimmick that comes down the pipe, then make the drug industry rich by taking their pills to treat the ailments caused by the crappy food and wrong exercise advice.

    Glen wrote on July 13th, 2013
  12. Mark,

    I’m curious, how do you define intermittent interval training, i.e., how long, how often, etc.

    Thanks!

    Jon

    Jon wrote on July 16th, 2013
  13. Mark,

    What do you consider, brief, intermittent interval training…how long, how often, etc?

    Thanks!

    Jon

    Jon wrote on July 16th, 2013
  14. I do a 50 min outdoor MovNat class 2X a week and then walk/hike/play with my kids on a regular basis. MovNat has been incredible! I am faster, stronger & more skilled than I was a few months ago. My trainer throws in sprints once a week and we jog between our outdoor stations, probably a total of a mile each day.Recently my husband and I went white water rafting (the real kind where you actually paddle and steer the raft yourself) and I was surprised that we did better than my chronic cardio training sister (runner) and brother in law (cyclist). There is something to functional movement = true fitness. Not only is running/cycling damaging- it is is linear. You never learn to move efficiently outside your center. Fitness that makes life easier is so much more beneficial in the long term. If you have a MovNat trainer near you and are the kind of person (like me!) that needs to have it scheduled and be held accountable I highly recommend it.

    Shannon wrote on July 16th, 2013
  15. I’m guessing/hoping that the following is NOT chronic cardio, what do you think?

    http://i.imgur.com/QmSj2DO.jpg

    At age 59, my max HR is 160 BPM, and once or twice a week I go on a five-hour bike ride, with an average HR of 120 BPM (75% of max).

    It sure is fun, it gets me off the couch, and I wouldn’t want to give it up.

    Al wrote on July 22nd, 2013
  16. @Glenn Good advice, what kind of workout are you doing these days?

    Nick T wrote on July 22nd, 2013
  17. First I have to admit that my own confirmation bias is rather strong on this subject (I love running a lot, so I run a lot), but still, I don’t think the general message of the article is fair, or accurate, so I wanted to share the following thoughts in response:
    1. The general idea articulated here regarding over working the heart through chronic cardio ignores the rather obvious point that cardio causes a significant reduction in resting heart rate. For normal people, even if you run an hour a day, and it only reduces your resting heart rate by 6-7 bpm, you are still going to see an aggregate reduction in daily heart beats. Thus, paradoxically, your heart is working less as a result of all that cardio. There is likely a point of diminishing returns, but I think it’s extremely rare for normal people to reach it.
    2. The study on AF is an interesting one, and the most difficult study cited here to explain away, as a chronic cardio guy. However, the study notes that, contrary to other references in the article, the effects of increased risk of AF from exercise are not persistent. The study concludes by stating that the increased risk of AF from exercise decreases over time, “probably due to the beneficial effects of exercise on other AF risk factors.” Other reviews of this study have concluded that the AF issues docmented here are “benign,” but please see my final point on this matter.
    3. You cite the 40% data point on athletes who develop persistent AF. However, the cited study combined both occupational and recreational activity in it’s “athlete” group and did not distinguish between types of exercise. Additionally, this study excluded individuals from its control group with other heart issues. Thus, the control group was probably healthier than the general population.
    4. The study cited on atherosclerosis has two problems: (1) The sample size is very small, and (2) the author of the study does not come to the same conclusion as you. He states the study “does not mean exercise is bad for your heart” but rather concludes that marathon running does not exclude you from potential heart trouble. He does not make the classic mistake of thinking correlation is causation.
    5. The study cited indicating walking is equally beneficial to running showed that running significantly reduced the risk of all of those diseases, and it appears that in showing the difference between running and walking they controlled for differences in BMI, which hardly seems fair. It’s kind of like saying- if we control for the benefits of running, then there doesn’t appear to be any benefits from running.
    6. Bone, joint and tendon issues are complicated matters. It seems that everyone has an anecdote that creates this causal relationship in their minds between running and long-term injuries. The research tends to show that bone issues arise when the muscles are weak, and admittedly, too many runners don’t do the necessary strengthing exercises. However, the research also consistently shows that running improves bone denisty over time. There are competing studies on what exercise is best for bone health, but running is generally good for bones.
    7. I found it rather conspicuous that you neglected to include any kind of data on mortality rates. Surely if running is so dangerous, it would decrease life expectancy, right? Comprehensive data collections overwhelmingly show that chronic cardio makes you live longer. As to the quanity of cardio on mortality rates, some have argued that there is a “U curve,” stating that there is a point of diminishing returns and once you reach around 60+ miles per week, your mortality is almost the same (but not worse) than sedentary groups. But again, that is only because of the controls placed on the benefits of running, such as BMI. Once those controls are removed, there is a nice correlation between large amounts of cardio and living longer.
    8. As a final point, I find it so interesting that so many of your readers believe that running makes you fat and unhealthy, and that their runner acquaintances are all fat and unhealthy. There seems to be strong confirmation bias in play because my anecdotal experience is diametrically opposed to theirs. But the next time I see a fat guy win the Boston Marathon, or the next time I don’t reduce waiste line and lose weight while training for a marathon (which is yet to happen), I will reconsider my opinion.

    Scott wrote on July 25th, 2013
  18. I read scientific study somewhere that said that running more than 20 miles a week actually gives more stress to the body than can be beneficial, but not exercising will also put you back.
    I strive for a mile a day either running or swimming. and one day off. So that puts me at a perfect 6 miles a week: not too damaging, but not too slothful either

    Lisa Being wrote on August 2nd, 2013
  19. I am new to PB. I started the Paleo lifestyle eating program August 1st. I am a 44 year old female who works nights and have for 22 years. When I began the program I was 305lbs. I am now 270lbs ( I was 264lbs on Xmas eve), I missed 3 days of exercise and had Ritz crackers with cream cheese for a Christmas treat. I am stunned that I gained 4 lbs back in a one “treat” day. It’s not sugar or milk chocolate or even ice cream! It’s very hard to comprehend the adverse effects those two items have had on my body. I have been exercising 7 days a week for one month-from the day after Thanksgiving to Xmas eve. I average about 2 lbs of weight loss per week and I’m not sure if I’m exercising properly. I have more weight to lose than the average person yet I tend to lose it at an extremely slow rate. I have been following the 7 day a week program and now wonder if I should double my efforts-maybe before and after work?? Should I do that, do the workouts need to mirror each other or should I stick with the PIC before work and just walk for an extra hour after work? I can’t sprint yet but my “sprint day” workout I walk at 3.7 mph for 30 mins and then I do a full body circuit weight lifting-I do this Monday, Wednesday, Friday and Sunday and then on Tuesday, Thursday and Saturday I walk for 1 hrs at 3mph. I usually eat 3 times a day and drink an emulsified veggie drink twice a day ( spinach, celery, cucumber, avocado, green apple, blueberries). I eat a protein and veggies for breakfast and lunch and a protein, veggie and a grapefruit for dinner. Any help and critique of my routine would be appreciated. Should I be concerned about the small amount of weight loss per week?

    April wrote on January 2nd, 2014
  20. What about Jiu Jitsu and Martial Arts…these considered Chronic Cardio

    Phillip Fletcher wrote on March 19th, 2014
  21. So running kills? maybe i should quit track, put on 20 pounds and do nothing again like when I was 12, because THATS the key to longevity!

    John wrote on May 20th, 2014
  22. Thank you for this article. I’m a perfect example. I am the gal that would run 5+ days a week either on the treadmill, trails, or at the local high school track running 4-5 miles at a time. To make a long story short, I recently had some blood work done and I showed a low WBC and an elevated fasting blood glucose level. I am certain it is the constant cardio to blame. I eat healthy–only carbs are rice and fruit in moderation, am thin, normal bp, normal cholesterol, etc. Through your other article, I am positive its the cortisol resulting from the excessive exercise that caused the elevated fbg and low wbc.

    Tessa wrote on June 11th, 2014
  23. Howzit Mark. Paper showing how resistance training raises VO2max!: http://link.springer.com/article/10.1007%2Fs11556-013-0120-1#page-1

    Charles Nankin wrote on September 16th, 2014

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