The role of fat oxidation in Well-trained (WT) versus Recreationally Trained (RT) endurance athletes

Hi. I’m referencing your Aug 2015 study ‘Rethinking the Role of Fat Oxidation: during HIIT in well-trained (WT) and recreationally trained (RT) runners’.
Please help my understanding on two questions:

  1. Why did the WT athletes continue to have a high FATox energy sourcing at a high % of VO2Max (approx 90% VO2max)? What was happening in their muscle cells that did not happen in the RT athletes?

  2. What training strategy should a RT level athlete undertake to work toward the WT FATox capability? I assume the answer is a lot of steady state endurance work at or below the VT1 threshold, e.g. what Stephen Seiler calls ‘ 80/20 Zone 2’ to develop the slow twitch mitochondrial capacity?

Thank you. I appreciate any feedback.


Thanks for the awesome question @Billcrow . Here’s a link to the open access paper for reference.

  1. Obviously we are making educated guesses as we don’t have any dedicated sensor in the muscle to confirm, however you would imagine that the WT athletes have more mitochondria in their muscle cells - the powerhouse organelles in cells that make the ATP. The WT group’s muscles were able to take more fat from the body to use as energy.

  1. I would agree with you. A training program like we prescribe in Athletica. And then if you want to add more fat burning ability, you can leverage nutrition (food timing and quality).

THANK YOU, Paul! Happy New Year! Bill

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Hey there @Billcrow , I would like to jump in here and echo @Prof 's post and share my personal experience with improving Fat oxidation. Zone 2 is effective but together with nutritional and lifestyle elements total dynamite :firecracker:.

I have a bit of a unique story in that I started long-distance triathlon training in 2018, aiming to qualify for Kona, but ended up binning myself. Did a lot of training, ignored recovery, and when I got injured, I increased HIIT training. I wasn’t disciplined enough to stay truly on zone 2 (and possibly wasn’t updating my zones frequently enough) but allowed myself to get sucked into the lure of zone 3.

Combined with high stress in the form of environmental, nutritional, and emotional stress added to the physical stress, with the mentality to Push Through No Matter What led me exhausted. Overtrained. Stress belly. Gained 5kg. Ate a typical endurance athlete diet, high carbs, was Hangry often, and fueled with fast carbs.

Had to take 6 months off. Thought it was game over for me.

Enter @Prof and Athletica!
we started to work on becoming fat-adapted:

  1. whole foods
  2. increased healthy fats (avocado, olive oil, nuts, fish, coconut oil)
  3. fasted workouts (started with 30mins runs, now I can go 6 hours on the bike without anything but a couple of handfuls of nuts while energy stable and feeling like a rocket ship. :rocket:
  4. paying attention to recovery, sleep, mood and opting for easy zone 1-2 ride instead of pushing through if feeling flat. Sleep is a big one. I used to get up at 4:30-5am to squeeze in a workout before the family was up. Now I “sleep in” to 6-6:30am and wake up slowly with meditation.
  5. yoga, meditation
  6. In other words, putting my health in the driver’s seat has made a monumental shift.

I’ve lost about half of the weight but more importantly, lost 10cm around my belly, my performance has improved but most of all I feel amazing and energetic in everyday life! I’m biking better and running free without shoving those nasty sports gels down my throat. The journey has been quite paradoxical if you follow the mainstream sports nutrition advice. Can’t wait to share more in the future…



Thank you, Marjaana! I appreciate your info. Hope you are doing well.

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@Prof as a major part in the traing sphere there is a chance to have some study reference or guidance regarding nutrition and integration?

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Dear @Trabucchi. I am happy to offer guidance and answer questions to the best of my knowledge here on the Athletica forum where I feel safe and valued. Just note that I have tried to put my 2c in elsewhere and it is interesting how aggressive (I feel) the counter comments go, even by scientists/doctors on that forum. So I will just say from the outright here as we venture into this domain that alternate viewpoints are welcomed (and encouraged) but please everyone keep the language respectful. For example, small minded name calling will not be tolerated.

Your note is timely also as @SimpleEnduranceCoach @Marjaana and I are currently preparing for a couple episodes on this.

So with that said => ask away…


I’m smiling reading this response and appreciated your commentary in the trainer road thread when I saw it several weeks ago. It’s disheartening to be on the receiving end, but take comfort in knowing you’re certainly not the first to be on the receiving end of a certain persons aggressive disagreement.


@Prof sad to read all this anger and poor discussion oriented minded in certain thread. Be sure my writing and thoughts will remain humble :grin:. Just now I only be interested in a general point of view regarding the use of creatine concerning the effective pruduction of ATP process in the repetitive athletics gesture it can effectively have a positive help? And BCAA an integration would be costrictive to recover faster between workouts sessions.


Thanks @Trabucchi,

As we often say in HIIT Science, context over content. Content is king but context is God.

Its probably no surprise that Creatine, the substance you’re trying to get more of in your muscles for energy production, is contained in high quantities in meat. And this, IMO, is the heart of the answer. On average, you can expect to find about 2 to 4 grams creatine per kilogram of raw meat or fish. Really its the same for branched chain amino acids. High levels in meat.

Therefore, in the context that you are a vegetarian or consume low amounts of meat or fish, you are likely to be a responder to creatine (and BCAA) supplements. In the context that you consume relatively high quantities of non-processed meat, fish and eggs, supplementation is likely to be superfluous.


Thanks @Prof for the point of view. As for me I try to keep a very good and Healthy nutrition base full of organic food , fat coming from avocado, extra virgo oil(which in Italy we are plenty off) , nuts( all sorts). I ll eat fish for omega 3 intake and meat and egs as well plus all sort of curcuma, jinjer ecc… Said so I nether than less introduce integration. As a personal experience I feel expetialy Bcaa and protein shake are working on my recovery making it faster. Are most of the times pratical for a snack. Let’ say to finish a 4-5 hour bike session and back at home at 11.00 is easy to take them plus a banana and after 1-2 hour have a complete meal.


Sounds like you have a very good diet and food timing @Trabucchi that works well for you. Keep trusting that ‘feel’. The little man or woman in your head knows more than we give it credit for sometimes…