Metabolic Testing and the Respiratory Quotient (RQ)

Here at TNN we work closely with Exercise Physiologists (EP) across Australia who conduct our metabolic testing (more specifically Resting Metabolic Rate and VO2max Exercise Testing). The data we obtain helps identify an athlete’s current level of fat adaptation and develop a more efficient day-to-day nutrition and sports nutrition/fuelling plan. The retest is then evidence to support our nutritional and fuelling guidelines and the metabolic efficiency changes that take place, following the implementation of our nutritional guidelines.

Recently I visited the Gold Coast to present a seminar on “How to Become Bonk Proof” (which means the avoidance of ‘hitting the wall’ in Australia by the way) and collaborated closely with Jupiter Health for athlete testing. I also signed myself up for testing so I could learn where both my metabolism and fitness were at during my extended off-season. I haven’t completed a VO2max test since my undergraduate days (i.e a long time ago!) but I was quickly reminded how tough they can be. For those of you who don’t know, it’s an exercise test of increasing intensity, until your legs stop moving or you hit stop on/ fall off the treadmill. I chose to complete my test on the bike as I’ve only been running minimally in the last six months.

I wanted to personally share my exercise test results with you, to specifically highlight the benefits of such testing, and to either assist you in interpreting your own results, or encourage you to have your test conducted to remove the guess work from your individualised nutritional plan.

Before we dive in, here are some important facts for you to know.

The facts

  • The universally accepted conversions are:
    – Carbohydrate (CHO) = 4 calories/gram
    – Fat = 9 calories/gram
  • Respiratory Exchange Ratio (RER) refers to the ratio between the amount of oxygen (O2) consumed and carbon dioxide (CO2) produced in the breath, determined by comparing exhaled gasses to room air.
  • Respiratory quotient (RQ) is calculated from the RER and is an indicator of which fuel (carbohydrate or fat) is being metabolized to supply the body with energy.
    – RQ/RER 0.7 = optimal fat burning
    – RQ/RER 0.85 = a mix of fat and carbohydrates
    – RQ/RER 1.0 = complete sugar burning
  • The data I share with you (to follow) doesn’t specifically state my RQ as calculations have been taken further to determine calories and grams of both carbohydrate and fat utilisation. Alternate reports often include your raw data and your progressive RQ, so the above information should be beneficial to you.
  • Fat burns in a carbohydrate flame. Think of a candle, where the wick is your carbohydrate intake and the base is your fat storage. You need to light the wick to access the base and tap into this large reserve of energy. The science behind this is based on a substance known as pyruvate. Pyruvate is formed during glucose metabolism and if glucose is not present, fat has nowhere to attach to the mitochondria, which can slows the metabolism, and halt or significantly decrease fat oxidation. So those of you going out riding for 5 hours with no carbohydrates, please stop. More on that here.
  • Replacement guidelines are a maximum of 50%. For example, if you are burning 60g CHO/hr, 30g CHO/hr should be sufficient from a fuelling perspective. There are many reasons for this, which the most significant being to minimise digestive requirements during training and racing. Digestion is a huge energy requiring process and consuming too much will direct blood and oxygen flow inwards, rather than outward to working heart, lungs and muscles, where it is most required at this time.
  • The Cross Over Point (COP) is the point at which your fuel utilisation shifts from predominately fat to predominately carbohydrate. To accelerate fat burning in training, the intensity should be kept <COP. As your fat adaptation improves, your COP should shift to right, giving you a much greater heart rate (HR) zone to train and race at. If you race at intensities greater than your COP, then your fuelling requirements will be higher and should be adjusted accordingly.
  • Prior to obtaining this data, a MAF Heart Rate, developed by Dr Philip Maffetone of 180-age is used to estimate optimal fat utilisation. This can then be personalised based on test data and adapted as the athlete’s metabolic efficiency increases. Please listen to Episode 45 of The Real Food Reel here.
  • Fuelling requirements are in a constant state of evolution. As your fat adaptation continues, you should continue to need less both in training and racing.
  • Please keep in mind that test results are very specific to the conditions of your test, the day and all the variables surrounding (training, nutrition, sleep etc). We must use this as a guide but continue to be intuitive athletes and test and adapt each training build.

My Exercise Test Results

Figure 1: Fuel Burning Profile – Cross Over Point (COP)  

TNN Fuel Burning

Data supplied by Jupiter Health.

As you will see, my COP is 171 beats per minute (bpm). This is advantageous as I can comfortably train and race at <171bpm and optimise fat oxidation. In athletes just commencing their fat adaptation journey, I commonly see COPs of 120-135bpm, which makes HR training zones more challenging to prescribe. As they adapt their day-to-day and sports nutrition, we shift this to the right and improve fuel utilisation at all intensities.

Figure 2: %VOmax Zones and Relative Fuel Burning  

Screenshot 2015-10-26 14.54.22Data supplied by Jupiter Health.

I selected a few key levels (average HR) to highlight the changes in fuel utilisation with increasing intensity. Personally I fuel off 25-30g CHO/hr, which is now supported with data here at intensities <167bpm (remember we go off a maximum of 50%). At 174bpm it is possible that my requirements could increase to ~50g CHO/hr but this is highly unlikely due to the fact that I still have a contribution of ~300 calories per hour (cals/hr) (I burn 600-650 cals/hr). Many athletes have a 0% contribution of fat at 80-90% VO2 max and this changes their fuelling requirements completely. In my experience, this is when nutrition becomes more of an art than a science, and specific experimenting is most beneficial. For support determining your fuel requirements at varying intensities, please work with a qualified and experienced Sports Nutritionist.

I find this data most beneficial when working with athletes and developing or adapting their training program. It is important to note that most generic VO2 max reports do not contain this data, as Mark at Jupiter Health has developed their protocol and analysis of raw data over many years. If you are unable to visit Jupiter Health due to location restrictions, please speak with your EP and request this data before conducting your test.

Finally, my average fat oxidation in this environment is 0.52 grams per minute (g/min). For decades science has told us that highly trained athletes range between 0.45-0.75 g/min and the absolute maximum is 1.0g fat/min. We now know, thanks to the FASTER (Fat Adapted Substrate Oxidation in Trained Elite Runners) study, that up to 1.8g fat/min is possible. That’s 972 cals/hr! More on this to come when the study is published in the literature later this year.

More information

VO2 max tests ranges from $200-300 and private health insurance rebates may apply.

For testing in Australia, please utilise one of the following resources:

  1. Jupiter Health
  2. Bodyology Physical Performance Solutions
  3. Exercise and Sports Science Australia (ESSA) to find an Accredited EP (AEP) in your area.

Alternatively, contact the Human Movement Department of your local University and enquire about becoming a subject in one of their research studies. This will likely be at no cost to you.

Please note: There is more that we can analyse from a VO2max test – this is just a snapshot of some of the work we do here at TNN.

For more information to learn about the soon-to-be published research in the field of fat adaptation and endurance exercise please listen to Episode 35 of The Real Food Reel here.


Croci, Ilaria et al. ‘Fat Oxidation Over A Range Of Exercise Intensities: Fitness Versus Fatness’. Appl. Physiol. Nutr. Metab. 39.12 (2014): 1352-1359.

Romain, A. J. et al. ‘Physical Activity Targeted At Maximal Lipid Oxidation: A Meta-Analysis’. Journal of Nutrition and Metabolism (2012): 1-11.

Spriet, Lawrence L. ‘New Insights Into The Interaction Of Carbohydrate And Fat Metabolism During Exercise’. Sports Med 44.S1 (2014): 87-96.

Venables, M. C., J. Achten, and A E. Jeukendrup. ‘Determinants Of Fat Oxidation During Exercise In Healthy Men And Women: A Cross-Sectional Study’. Journal of Applied Physiology (2004): 160-167.

Questions? Please post below and we look forward to assisting you.

To book your complimentary 15-minute consult and find out how we can help you here at TNN, please click here.


  1. runnerD

    Thanks for the interesting read! I just had some metabolic testing done after trying HR training using the Maffetone (180-age) method for several months and not really seeing improvements. I was running extremely slowly to stay below my MAF rate, not much faster than a fast walk/shuffle (~7.5 min/km). My test results showed that my COP occurs at a very high heart rate ~185-190 bpm. Now I’m not sure how to proceed in terms of training – Maffetone recommends running at just below COP heart rate to optimize training, but it seems a little crazy to train at a HR of 190 bpm (I’d have to be -10 years old according to the maffetone formula..). I’m thinking these results may explain why I’ve always been a slow runner and unable to get faster – I can’t actually do any sustained training at my real MAF heart rate long enough to improve.. do you think this is a possibility? Your COP also occurs at a pretty high HR – do you find it difficult to sustain that HR over long training sessions?

  2. Steph

    To answer specifically I would need to see your full test results, but for you it sounds like a combination of intervals using your MET results, with long/base training at MAF. Make sure you’re conducting a MAF test regularly as you shouldn’t be at 7.5 min/km for long if you are doing it correctly.

  3. Gregory Cox

    Hi runnerD,

    Firstly let me make it clear that I’m not an expert, but I have been following the Maffetone method for 2 months & I have studied and absorbed the contents of the 180 formula blog. Your statement “Maffetone reccommends running at just below COP heart rate to optimise training” is incorrect. There is a huge difference between your MAF HR and COP. At COP by definition you are burning equal amounts of Fat & Carbohydrate. At the MAF HR you are primarily utilising fat as your fuel source. If you look at Steph’s Fat Burning Profile above you can see that the sweet spot for burning mostly fat is around mid 120’s to mid 140’s. My suggestion is to direct your query to Ivan at There is plenty of evidence that the Maffetone method works, but it is slow initially and you do have to be patient!


  4. Alex Fergus

    I have a question – based on the numbers above, wouldn’t your most optimal aerobic base building HR be at 146bpm? This is the HR that had the highest fat burning rate (36g vs the 35.6g at the higher 167 HR).

    Wouldn’t this figure (146) be closer to your MAF number? Even though your fat burning rate is very similar at 167, wouldn’t the extra stress due to the increased intensity potentially be detrimental to your training and recovery in the long term?

    Sorry if I am missing something here, I am new to the world of MAF and aerobic training.

    Also – I am in Sydney, do you know of any clinics here in Sydney where I could test my RQ? Oh, and final question, can you do these tests on a rowing machine? I’m a rower not a cyclist 🙂

  5. Steph

    Hi Alex, yes 146bpm is optimal but there are stil benefits to training

  6. Bruce Gray

    The FASTER study uses a low carb diet of 70% fat and 10% carb.
    I seriously question what that does for gut health and the microbiome, which science is now suggesting require a daily fiber load above 50grams.

    An athlete consuming 3000 Calories / day, and taking 300 Cals as fibrous carbs, would need 12 cups worth.
    At approx 80grams/cup, and fibrous carbs averaging 2% fiber by weight, that would provide around 20grams of fiber.

  7. Min Benstead

    Hello Bruce, FASTER is just one example of the application of a low carb diet and here at TNN we don’t personally recommend <10% of carbohydrates. We also recommend higher fibre intakes and many additional gut health practices to ensure the longevity of our unique LCHF approach. We do offer a complimentary skype consult if you would like to discuss an approach unique to yourself?

  8. Jack Heslin

    Hi Steph, great informative article. How do we locate where we can take an RQ test?

    Kind Regards,


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