Bite-Sized CrossFit Concepts: “Cardio”

(or Why We Don’t Program “Murph” Every Day)

For today’s bite, let’s take on the elephant in the room: cardio.

The mainstream fitness prescription calls for spending hours and hours “burning calories” on the treadmill (or elliptical, or exercise bike, or whatever the cardio machine du jour happens to be.)

We do not like this. Here’s why.

Long duration “cardio” is exclusively aerobic training, utilizing the oxidative pathway (we’ll talk more about this in a future Bite-Sized CrossFit Concept.) Aerobic training improves cardiovascular function and decreases body fat. However, it also decreases muscle mass, strength, speed, and power. This is why you find marathon runners who can only jump a couple of inches off the ground!

We want to produce athletes who are equal parts track athlete, gymnast, and Olympic weightlifter: strong, fast, and powerful. We want to decrease your body fat and give you a huge strength to bodyweight ratio so that you can win American Ninja Warrior and look amazing doing it!

Anaerobic training — short duration, high intensity intervals — is the only way to achieve this. It improves cardiovascular function, decreases body fat more effectively than aerobic training, and dramatically improves power, speed, strength, and muscle mass. In addition, anaerobic training can be used to develop a very high level of aerobic fitness. In English, this means that short duration interval training will develop your ability to take a nice long run as well as PR your “Fran” time.

To summarize: stop worrying about how long you’re spending working out, and start worrying about finding that intensity in every session!

Food For Thought

Do you often find yourself lying on the floor gasping for breath after a workout? If not, why not?

Learn More

Forget The Fat-Burn Zone: High Intensity Aerobics Amazingly Effective by Clarence Bass
What Is Fitness? by Greg Glassman

Have Questions?

Ask them in the comments!

Bite-Sized CrossFit Concepts is our series of quick primers on some of the fundamental principles of CrossFit, as well as common misconceptions and frequently asked questions. We hope that they will help you understand why we do things the way we do, and train smarter!

Share This Story, Choose Your Platform!


  1. Ajay July 13, 2014 at 10:20 am - Reply

    Great read, hope to see more of these!

    • K July 23, 2014 at 11:36 pm - Reply


      Well said! I think we agree on all fronts. I was only objecting to the idea that the “mainstream fitness *prescription* calls for spending hours and hours ‘burning calories’ on the treadmill” (emphasis mine). As you note, the “overall trend” in the fitness world is in fact more toward prescribing HIIT, not lots of lengthy low-intensity cardio. Crossfit, in that sense, is a particularly fun and effective form of an existing trend.

      I agree that a survey of what people actually do at the gym would likely reveal way too much low-intensity cardio. I just disagreed with the original post’s suggestion about what the “mainstream fitness *prescription*” was . (I do, btw, consider Men’s Health and such to be offering fairly “mainstream prescriptions.” )


  2. K July 13, 2014 at 6:01 pm - Reply

    “The mainstream fitness prescription calls for spending hours and hours ‘burning calories’ on the treadmill….”

    Does it really? Or have you set up a straw man here? Can you provide a link? Do you have a link, for example, to a mainstream program actually recommending “hours and hours” on the treadmill without high-intensity training, as you suggest?

    My impression is that “mainstream” fitness folks have been recommending high intensity training for a long time. Even long-distance running experts recommend high-intensity interval training as a crucial component of a training program.

    Here’s a recent men’s health article recommending interval training for runners, for example:

    Here’s another :

    And another, from Runners World:

    It seems to me that crossfit is pretty much in line with the “mainstream” thinking here. I enjoy cross fit, but it’s just a variation on what is already mainstream. It’s not radically different in its theory. No serious “mainstream” program recommends “hours and hours” on the treadmill as the only or best way to get in shape.

  3. Kyle July 23, 2014 at 4:54 pm - Reply

    K, I think the point is that while that may be the case for “mainstream fitness folks,” most people (or at least most Americans) do not regularly read publications like Runners World or Men’s Health, and while more attentive individuals are likely plugged into the overall trend towards HIIT, the idea that getting fit means “hitting the treadmill” or the is a longstanding trope accepted by broad swaths of the country. A more instructive metric would be a survey of what people do when they exercise or go to the gym, which I would still assume is heavily biased towards cardio.

Leave A Comment