Athletic training: a game of physiological Jenga.

The 80-20 rule in athletic training* goes like this: train 80% of the time at a low intensity and 20% of the time at a high intensity, and you’ll achieve the best results.

Understandably, a lot of people—particularly us urbanites who are extremely busy and almost completely devoid of free time—might say: “but I only have a few hours to spare every week! I can’t afford to run slowly 80% of the time. How can I possibly expect to make gains?”

(Or something like that.)

This is exactly the wrong question. What running (a.k.a. training) at a low relative intensity—which people often refer to as “running slowly” does for the body is that it develops the aerobic system. (For most, but not all of us, training at a low relative intensity does indeed mean running slowly.) The aerobic system is extremely important: it mitigates oxidative stress (also known as chemical aging), it helps us recover from anaerobic efforts by processing lactate, and it keeps us well-fueled over the long-term by burning fats.

The aerobic system is the very foundation upon which any “gains” are built. In this sense, aerobic training increases what I like to call our “physiological capital,” that we can invest in high-intensity (anaerobic) training and develop what we typically refer to as “strength” and “power.”

To explain this relationship, I like to use the metaphor of a Jenga Tower.

Suppose that you have a particular strength or power goal: you want to run 6 minute miles. This is equivalent to wanting your Jenga tower to be 10 levels tall. But the problem is that you only have 20 bricks (each full level of a Jenga tower is 3 bricks).

The result is that you can only build 6 complete levels to your Jenga tower. You’re faced with a stark choice: you need to add levels to get to 10. But you don’t have any more bricks. So you’re forced to take from the lower levels. (This is essentially what strength training does). Your tower gets higher and higher—which is fine, until you pull out or lay a brick juust too quickly or a light breeze comes along—and the tower, which had grown increasingly unstable, plummets to the ground.

(You’ve just become injured.)

But there’s a way to add bricks to the base of your tower: aerobic training. This is what I mean by “increasing our physiological capital.” While aerobic training adds bricks at a pretty good rate, left to its own devices it turns your tower into a pyramid: the lowest level grows wider, until at some point  your body decides to start growing the next level.

That’s not a bad thing: a lot of ultrarunners (the healthy ones) have metabolisms that look like a shield volcano: gargantuan aerobic systems, but very little power. (If the height of the tower is how much power you possess, then the width of the base is how much distance you’re good for.)


That said, it’s not necessary to build a pyramid, when it’s a tower you want. Although it’s important that your tower be stable, that’s about it: most of us are not trying to be an ultrarunner, nor do we have to be. All you really need is a few extra bricks around your base—enough to plug any holes you may have created, and to be able to add a couple of levels. Rinse and repeat.

A quick disclaimer: the body doesn’t convert the actual aerobic machinery into anaerobic machinery in the way that a naïve reading of the “Jenga metaphor” would suggest: the brick that you take from the base is not literally the same one you put on top of the tower. However, the reason I like the Jenga metaphor is because the stress and wear-and-tear incurred by anaerobic work (compounded by the fact that it is the job of the aerobic system to absorb those stresses), means that the process of adding strength and power basically always means carving into your aerobic base.

How often do you switch from adding bricks to adding levels? If you’re looking to run an endurance race, for example, then you need a very wide aerobic base.

Supposing that you want to develop some all-around fitness, a basic (but certainly not universally applicable) recipe is this:

  1. For 2 weeks, train primarily easy 95-100% of your training.
  2. The next 2 weeks, train at a moderate-to-high intensity 35-40% of the time.
  3. Rinse and repeat.

This process will give your body two weeks to recover well from strength training (read: replenish the bricks you took from the base, and add a few more). Two weeks of low-intensity training isn’t really long enough to start losing high-end fitness: the small amount of strength training 0-5% during the easy weeks is more than enough to maintain your gains. But when you’ve cycled through this process several times is when you’ll really start to see your gains stack up.

Building and maintaining an aerobic base, and making sure that our strength gains are well-buttressed by wide lower levels of our metabolic tower, is non-negotiable. Some of us are lucky: for good or ill we spent our formative years playing at the beach, kicking around a soccer ball, or going hiking with our oudoorsy parents. This person (unbeknownst to them) has been stacking more and more bricks around the base their fledgling tower, broadening their aerobic base until they’ve accrued what seems like a limitless amount of bricks.

Others never had that chance.

But not having had that chance doesn’t mean we have any more of a choice. Sometimes, the unconscionable choice—running “slowly” despite the horrible feeling that time is slipping away and we’re not getting any faster (forgetting the fact that our pool of bricks is growing ever larger)—is also the right one. That choice will put us in a position from which we can develop speed . . . and get to keep it.

*NOT the Pareto Principle.



12 thoughts on “Athletic training: a game of physiological Jenga.”

  1. I’m a MAFer. No, not an MFer, a MAFer. 🙂

    I love your insights from Phil’s blog and the Maffetone Method FB page.

    I’ve got a question that I’m hoping you can provide some insight to.

    For many years (off and on since I was 18. I’m now 46) every time I ran it was as hard as I could. Uneducated, I felt that was the path to improvement. I’ve always been much slower than any of my training partners and my HR has always been significantly higher if we were working at similar intensities.

    Now that I’ve taken up the MAF method (Sporadically since August ’15 – exclusively since Jan.1) my improvements are minuscule.

    I’m athletic and used to consider myself fit. MY last race was a Spartan Beast and I finished in the top 8% – I state that for perspective.

    MY wife is not in very good shape. She hates running. However, when she does run, or do any type workout like cycling or rowing, she can work much harder than I can with regard to HR.

    My question is this;
    Do you think all those years of super high intensity running (as hard as I could. and sometimes as many as 10 miles) has deranged my aerobic system?


    1. let me correct that statement about my wife. She goes to Zumba classes and does stay in, at least, average condition. She just doesn’t take her fitness as serious as I do.


      1. Redness44:

        It’s unlikely that your aerobic system is broken beyond repair, if that’s what you mean. But what running fast for all those years may have done for you is telling your body in no uncertain means that it better wire itself away from fat-burning and towards sugar-burning. Once it’s done that for long enough, that’s when you start seeing reductions in your endurance speed: it needs fat-burning to produce it, and you aren’t really burning fats in a big way anymore.

        The big question, then, is how do you impress upon your body that it needs a more hybrid use of fuel. But before I go on, let me make a quick note here. If you look at a lot of my posts, you’ll see that I often paint the body with a broad brush, using metaphors and similes to explain quite specific things about the body—like my comment now: “how do you impress upon your body…” rather than “how do you train Type I fibers” or whatever. This is because that’s essentially how the body thinks: it’ll grow much faster and more readily in whatever direction you want it to if you give it a REASON to do so, than if you give it a dose of a particular kind of training that in theory should have effect X, Y, or Z.

        This can help you build a rationale for why you want to try training A, periodization B, or workout C, for example.

        But let’s get back to the question: how do you give your body a REASON to use the aerobic system and burn fats? If you look at how the aerobic system works, this basically gives you 3 ways of addressing it: (1) lowering your lifestyle stress levels, (2) reducing the amount of carbohydrates in your diet, and (3) increasing the (a) amount and (b) duration of low-intensity training.

        For example, lowering your stress levels can be as simple as developing a ritual that you do every day that you get off work, or something like meditating 20 minutes a day. My favorite way of reducing the amount of carbohydrates in the diet is by slowly replacing them with veggie saturated fats but particularly MCTs (medium chain triglycerides) such as those in coconut oil, which increase the metabolic rate as well as fat-burning.

        But in my opinion, the most powerful thing you can do is increase the duration of your bouts of low-intensity training. To be specific, I’m not talking about developing your aerobic system, particularly when it’s already working relatively well: you can do that with shorter durations. But if you want to switch towards becoming more aerobic, increasing the duration will give your body that reason: it’s not just burning fats because it’s at a low intensity—it’s burning fats because its at a low intensity AND because if it doesn’t burn fats it’ll run out of sugar, and be completely exhausted. THAT is the incentive.

        Here’s a way to do it: figure out a comfortable distance that you can run long at the MAF HR without getting exhausted, but feeling it, and do that run once a week. Every 2 weeks, add 5 minutes to your run. Remember, this is NOT about getting exhausted: it’s just about impressing on your body “no dude, I don’t want high-intensity fuel (sugar) all the time. I’m asking your for long-duration fuel (fats) now.”

        So, if you feel that at some point you need to reduce the rate of increase or stop increasing for a while, in order to not get exhausted, that’s perfectly fine.

        A few pro tips:

        1) If you modestly (read: MODESTLY) increase the percentage of fat intake (particularly MCTs) and modestly reduce the percentage of carbohydrates (particularly high-glycemic carbohydrates) the 2 meals prior to a long run, you’ll burn more fats.

        2) Doing a 15 minute warm-up, starting 20-25 BPM below MAF and ramping up steadily up to MAF before your long run (or as the initial portion of it) will help you burn more fats. It’ll let the aerobic system kick into gear and reduce the need for your body to cold-start, which ups your stress hormones, increases sugar-burning and reduces fat-burning.

        3) Similarly, doing a 15-minute cool-down at the end helps your body transition into recovery, reducing post-exercise stress and further promoting fat-burning.

        Liked by 1 person

      2. Thank you so much for your reply Ivan. It’s helped a lot. I’ve been very disappointed that I’ve seen very little improvement in 6 weeks of MAF work. It’s made me start to wonder if I had just gone too far in the past.

        Liked by 1 person

  2. Another point about fat burning/aerobic. I did a lot of aerobic training last year for a mountain race, since then (October) my training has been much less. I got a virus around Christmas time and did hardly any training in January (I was also busy with work). This week I did a 4hr mountain climb (2nd half through deep snow). At the start it was very steep with little chance to warm up properly, I felt slow, sluggish and out of shape. However after about 1 hour I could almost feel my aerobic base ‘kick in’ and I started to feel better and better and felt great towards the end.


    1. James:

      For sure. It’s interesting how that happens. There’s this issue that I haven’t figured out how to tackle in a simple and accessible way (without boring people with heavy science) about what happens when, during aerobic training, the body transitions from using partly muscle glycogen to using glucose that the liver produces itself (a process called “gluconeogenesis).

      Having this internal engine churning out glucose, while your muscles are mostly powering your workout with fats, may be a big factor in staving off exhaustion.

      I relate this to a car switching from 4th gear into 5th gear.


  3. Hi Ivan
    I’ve got a race coming up in 8 weeks that I want to be in great shape for. However over the last months I’ve felt more fatigued than usual – not constantly (I think its constant changing work shift pattern) and I’ve had some training sessions when I have felt really good but also had some nagging injuries. I’ve done hardly any anaerobic training this year either because I’ve felt tired physically or mentally or because I’ve been time crunched and felt that if I could only fit in a certain amount of workouts in a particular week then it would make more sense to keep them strictly aerobic.

    What do you recommend for the next 8 weeks just keep the training aerobic and hope to go in fresh but maybe slightly overtrained?


      1. Hi Ivan
        It’s just over 10 miles (17km) off road on trails (decent surface trails though not really technical), hilly but not mountainous/


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