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Metabolic Efficiency 101

Written for beginnings, by a beginner.

After I posted my new and improved training plan, a lot of you wanted to know more about this Metabolic Efficiency Training (MET) business. Which I’m happy to share with you. Just keep in mind that my background is in politics and I currently work at a brewery. If you want to analyze the upcoming elections and discuss what fall beer would pair best with Meet the Press, I can go on all day. Science type stuff is not my forte. BUT, I do enjoy learning and I’ve been studying up to educate myself on all things MET, Maffetone, and heart rate, so I’ll share some of that knowledge with all of you. (*also note that I’m combining principles from Maffetone and MET under the same umbrella of “metabolic efficiency.”)

Here’s the skinny on fat adaptation:

What is metabolic efficiency? 

Using exercise adaptation and nutrient manipulation to become better at burning fat.

Why the heck does this matter?

Because we’re wired to operate on fat. With the ability to store only 2,000 calories of glycogen and 80,000 (or more!) of fat, we could theoretically run for days without needing much for fuel. Additionally, for us endurance athletes, 99% of the races we’re running (or triathloning) are in the aerobic, fat-burning zone. But, most of us have trained our bodies to rely on carbohydrates for fuel which restricts our ability to tap into those fat stores.

If you can help your body adapt to using fat for fuel, you can become a more efficient runner and be less dependent on carbohydrates for energy. This helps us: perform better, avoid GI distress, reduce our chances of bonking, and halt increased cortisol production (which can slow tissue healing and hurt our immune systems, reducing our ability to recover and upping our risk of injury).

How do you train your body to adapt to fat burning?

Two things matter: exercise and nutrition.

1) Exercise adaptation.

Let’s start with the basics: when you run (or partake in any form of exercise), you are either operating at an aerobic level or an anaerobic level. An aerobic effort is a much easier effort than its big brother. When you’re aerobic, you use fat as the main fuel source. But when you’re anaerobic, you need those carbohydrates to sustain the higher effort.

If you focus on improving your aerobic fitness, you can increase your production of fat-burning mitochondria and train your body to burn fat faster and longer.

2) Nutrient manipulation

The other half (or more, according to reliable sources) is nutrient manipulation. Let’s start with the basics here too: there are three macronutrients (fat, carbs, and protein) and when you eat them and how much you eat of them matters a lot. (#science) Refined carbohydrates and grains or too many carbohydrates period can train your body to rely on carbohydrates for fuel because carbs can cause your insulin levels to spike, which reduces your ability to burn fat and increases your need for carbs. It’s a vicious (and, at times, an absolutely delicious) cycle. The goal behind the nutrition side of MET is to stabilize your blood sugar and optimize your ability to tap into those fat stores. 

How you do you know when you’re aerobic or anaerobic?

The only surefire way to tell if you’re in an aerobic or anaerobic zone is by measuring your heart rate. Everyone has a maximum aerobic heart that tells you what your ideal fat-burning zone is. 

The best way to measure your heart rate during activity is with a heart rate monitor. I am currently using the Suunto Ambit 2 , but there are also many other garmins and GPS devices that come equipped with heart rate monitors. Or you can get a more affordable Heart Rate Monitor that just measures heart rate without shoving pace/distance/ALL of the data in your face. (I’ve also seen a lot of good deals on LeftLane <—referral link also gets you some bonus cash off your first order.)

How do you find your maximum aerobic heart rate?

There are two main ways to identify your maximum aerobic heart rate:

1) The 180 Formula

This was the brainchild of Maffetone after seeing the 220 formula fail to work on a number of athletes he was working with. Over a period of 30+ years, he used thousands of lab-based results to develop the 180 formula. This formula has athletes subtract their age from 180 and then modify that number based on a number of other factors (like injury history and training consistency).

Obviously heart rate is a very individual thing but the 180 formula has proven to be a reliable way to determine maximum heart rate for athletes unable to access full tests. There are also tests which Maffetone encourages athletes to use when heart rate training (MAF tests) and you can use those results, the amount (or lack) of progress, and perceived effort to help fine tune your target heart rate.

2) Metabolic Testing

If you have access to a clinic that performs these tests and the resources to justify taking them, you’re going to get the most accurate results from doing this. These tests will be able to identify the exact point at which you switch from fat burning to anaerobic sugar burning and you’ll walk away knowing your anaerobic threshold and maximum aerobic heart rate.

I know my maximum aerobic heart rate, now what?

Train under it!

According to Maffetone, the ideal way to develop your aerobic system, is to train within 10 beats of your max HR (so if your max HR is a 150, you want to train between 140-150), but he also makes a case for training at all levels beneath your max HR so you can develop the full range of aerobic muscle fibers. He encourages using warmups/cool downs to do this more effectively.

If you do this correctly, you will achieve a higher level of fat burning and improved aerobic performance. (For example: if you start out running a baseline of 9:45 minute/miles with a max HR of 150, that pace will get faster and faster over time while you stay at a 150 HR).

For more information from people who actually know what they’re talking about, here are some resources that I’ve been using:

Books, Articles & Interviews:

The Big Book of Endurance Training and Racing-By Phil Maffetone. A bible for all things Maffetone & endurance sports 

Metabolic Efficiency Training-By Bob Seebohar

The Maffetone Method-Also written by Phil Maffetone

Metabolic Efficiency: Becoming a Better-Butter-Burner-By Sunny Blende for Ultrarunning Magaine

Metabolic Concepts in Returning to Running-Joe Uhan on iRunFar

An Interview with Endurance Expert Phil Maffetone-Interview on Will Run Longer

Metabolic Efficiency FAQs-Bob Seebohar’s Blog

What is the Maffetone Method-Phil Maffetone’s website


Speed Up by Slowing Down with Phil Maffetone on Trail Runner Nation

Carb Burning Vs Fat Burning with Sunny Blende on Trail Runner Nation

The Power of Aerobic Training with Phil Maffetone on Endurance Planet (a little triathlony for me, but still full of good info on the nuts & bolts of Maffetone training)

Burning Fat, Training Slower and the 1:59 Marathon with Phil Maffetone on Runner Academy

Anectodal Success:

Larisa Danis Interview on Ultra Runner Podcast

Larisa came in 2nd at the 2014 Western States, is chasing an OTQ, and is reppin’ the US at the 100k World Champs.

Running and Racing with a Heart Rate Monitor with Gary Gellin on Trail Runner Nation

Gary Gellin usually has a single digit number for his finish place at ultras and continues to race well as a master.

Mark Allen Interview: A Look Back at Working With Phil Maffetone and What It Means for Today’s Triathlete

Mark Allen went from six DNFs/not wins at IM Kona to six consecutive wins with the final one as a 37 year old. He’s Maffetone’s first proof that training slow to race fast might actually work.

***As a final note, I should stress that everything in life and in endurance sports is very individual, including what works for your physical activity and nutrition. One of the things I like about Maffetone, is that he never prescribes a one-size-fits-all plan, and instead gives you tools to find out what works for you. Using MET is a big trial for me and one that may or may not work. My goal is not to endorse this method for the entire internet, but to fill you in on what I’m experimenting with and why. Expect to see updates (that hopefully show progress!) and more information as this experiment continues over here in Eugene.***

23 Responses to Metabolic Efficiency 101

  1. I switched over to MAF training about 4 months ago and I never want to go back. It is so much easier on my body and I am seeing MASSIVE improvements. It has been great!

    • That’s awesome to hear! Did you radically change up nutrition too or have you mostly focused on the heart rate side of things?

  2. Super interesting information!! Great post!

  3. So what beer would pair best with Meet the Press?

    This is awesome, thanks for sharing. I’m really intrigued to do more research!

  4. I’ve heard more and more about this from some of my fav runners (like you) that I’m inclined to try it. It’s definitely given me something to think about. Thanks for all the links!! Super helpful!

  5. Oo im intrigued too – keep us posted! I think I just have a fear of being hungry ;)

  6. Based on the 180 formula I should be targeting 145. Even on a relatively easy run I typically average 160+, which means I’d have to slow down a LOT to stay under. Have you found the same to be true? Is this normal?

    • Yes and yes. I don’t usually look at pace during my runs but I think I was averaging somewhere around a 10 minute mile to stay under my heart rate yesterday and I’m walking a lot more hills than normal. I think most people experience a lot of shock/frustration/disbelief with just how slow they have to run at first.

  7. I hardly recognize you! Who is this blogger who writes articles like this?!

    I’ve been training with heart rate for almost a year now. I started doing it with a coach and now I do it on my own less formally. I definitely think it works! It’s definitely frustrating at first because you have to run seriously SLOW but it pays off! And I also find it way easier to motivate myself to run more miles at the slower pace because it is less tiring mentally and physically.

    • It definitely is easier to get out the door when you know you only have to run REALLY easy! It’s good to hear it’s worked so well for you! I’m excited to see what happens with it.

  8. I love this post Emily (have really enjoyed all of your most recent posts, keep them coming!)

    I’m interested to know what you’ve really had to tweak in your own diet/training to embrace MET, and how hard it has been? Is there still room for beer??

    • “Is there still room for beer” might be the most important question of all.

      • I’m going to post more about the nutrition piece (probably on Friday), but yes, there IS still room for beer in my long-term nutrition plan. I don’t care enough about shaving a few seconds off my time to eliminate beer from my life. But, I have been doing a shorter term experiment in which there was no beer. I’m currently on my 11th (!) day without a delicious pint of beer. Luckily, I’m almost done with it and will most definitely have something in the IPA family to celebrate.

  9. GREAT post. I think you are absolutely approaching this in the right way and really doing your research. While I started by using the 180 formula, when/if you have a test done to find your max HR you can use a more person-specific formula based on your max HR to set your “zones.”

    Walking was totally defeating to me at first but I KNOW it has improved my overall fitness and just for reference my Z2 pace improved SIGNIFICANTLY over 2-3 years…with tweaks also made on the nutrition side in the last 2 years, I have been seeing BIG time improvements and increased endurance levels.

  10. My first experience with HR training after offseason was two months of horribly frustrating slow runs and then a massive PR that I had no business getting. So, I’m a believer. After doing it for a while, you almost don’t need to wear it all the time because you just KNOW what’s going on.

    I have to admit you were one of my holdouts on continuing to eat lots of carbs (Emily is an awesome runner and eats glorious carbs so therefore I need to eat lots of carbs to be awesome – that’s how it works, right?) Then, it seemed like every one went higher fat and thrived and I held out forever and then finally this summer I cut out (mostly) wheat and rice and went to potatoes and corn for carbs and wow, if I didn’t notice a change in my GI tract within a few weeks – losing a few lbs didn’t hurt either.

    Keep us in the loop with your experiment!

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