top of page

InsideOut client: Phil Mooney... Metabolic Magic at the Cellular Level!

Caroline Kavanagh | Jan 12, 2022

Over his mouth and nose Phil wears a rigid blue plastic mask, which carries his exhaled breath through a long clear tube to the metabolic analyzer. Across his chest is a heart rate monitor. I'm positioned by his side cranking up the pace on the treadmill every four minutes. When we are done, he will know precisely what kind of shape he is in and what he can do to continue to make further fitness improvements.

Mooney, 29, is among an increasing number of athletes — from professionals to out-of-shape first timers, turning to metabolic testing for advice on how to get fit. I contend that the key to a successful nutrition and training program is based on science and catered to the individual, all the way down to the cellular level – mitochondria.

Since 2012, I have been making it my mission to bring physiological tests, once reserved for elite athletes, to everyone striving for a faster time on the course or a lower number on the scale.

There are many different kinds of nutritional and training approaches out there, but when it comes to the exercise piece, folks typically opt for the same high-intensity approach. This HIIT style training is all the rage, but going supersonic in every session can lead to a host of complications, some of which include – over-training and injury. Typically my articles are focused solely on nutrition but here I am going to outline the physical training piece of the metabolic puzzle. Then I will showcase Phil Mooney's recent Metabolic Efficiency Assessment in order to describe that “magic” exercise intensity that is crucial for endurance athletes performance and success. Relationship between Metabolic Efficiency Point (MEP) and First Rise in Lactate Concentration While training in all zones is needed, the sweet spot in metabolic efficiency is Zone 2 as this is where performance can be dramatically improved if done correctly. Training just below this FatMax inflection point stimulates the oxidative energy system to the fullest. The Metabolic Efficiency Point (MEP) or FatMax is when fat oxidation is at its peak. Also happening at this same inflection point is the first rise of lactate concentration. [J Achten1, A E Jeukendrup]

In order to pinpoint this inflection point to maximize performance, physiological testing is the only manner to accurately be able to obtain this information. I have seen wildly different results in athletes that I have tested and therefore the so-called predictive heart rate calculations based on age do not necessarily apply. There are variations that normally occur even with the same athlete during different training cycles. These individual variations and details make a significant difference depending on specific goals throughout the year.

Why is Zone 2 training so crucial for endurance athletes performance? Training in Zone 2 (below MEP) is the environment that evokes maximal physiological benefits.

The advantages are.... • Fat Utilization:

Type 1 (slow twitch) muscle fibers are stimulated, this prompts mitochondrial growth and function which improves the muscles ability to oxidize fat. This is key in athletic performance because by improving fat burning we preserve glycogen utilization throughout the entire competition. Athletes can then use that glycogen at the end of the race as high intensity exercise continues and lots of glucose is being utilized.

• Lactate Clearance: Type I muscle fibers are also responsible for lactate clearance. Lactate is the spinoff of glucose usage which is used in large amounts by fast twitch muscle fibers. Lactate is mainly produced in fast twitch muscle fibers which then, through a specific transporter called MCT-4, export lactate away from these fibers. However, lactate needs to be cleared or else it will accumulate. This is when Type I muscle fibers play the critical role of lactate clearance. Type I muscle fibers contain a transporter called MCT-1 which are responsible for picking up lactate and transporting it to the mitochondria where it is reused as energy. Therefore, Zone 2 training increases mitochondrial density as well as MCT-1 transporters. By training in this zone you not only improve fat utilization and preserve glycogen but also increase lactate clearance capacity which is key for athletic performance.


Phil Mooney's latest Metabolic Efficiency Assessment and what he has accomplished over these past months in regards to his metabolic "alchemy."

............................................... Phil's Assessment: ............................................... Client: Philip Mooney Date: Dec 28, 2021 Age: 29 years

RESULT: Assessment shows MEP occurred at a heart rate of 175 beats per minute (bpm) and a pace of 7:35 min/mile. Below this heart rate and intensity, he was more efficient at using fat as an energy source. He begins to burn a higher proportion of carbohydrate beyond this intensity.


The first page of Phil's report (chart above) shows his Metabolic Efficiency Point (MEP) or FatMax. Phil's heart rate range before his FatMax is up to 174 bpm. This is an enormous aerobic range and not something I see frequently! This inflection or crossover point (RER of .85) establishes the heart rate in which fat and carbohydrate are being oxidized equally. After this point fat burning decreases and carbohydrate oxidation increases. Remember scientific studies have also shown, there is a correlation at this same inflection point to the first rise of lactate concentration.

From the test data, optimal fat burning training zones (chart below) are established. In "metabolic efficiency speak" we call this MEP - Developmental Zones (otherwise known as Zone 2 and below).

Phil has been in Base Phase of his run training cycle and was targeting his Zone 2 and below heart rates based off his previous test result. Given this recent result he has reset his Zone 2 heart rate target – up to ~173 bpm. Really impressive data! Because Phil's Zone 2 heart rate peak is relatively high, his pace can be faster while still eliciting the highest stimulus for further mitochondrial function and lactate clearance capacity. Real data to mark his progression as he continues in his Base phase of training.

Phil's target race is not until August so he has plenty of time to keep making gains. He played football in high school and took up running as an activity that he can do for a lifetime. His consistency and continued improvements are broadening. He also retests every six months to be sure his training is hitting the mark.

What are his performance results? Phil flat-out wins run races!

Summary: The purpose of each training zone is to elicit specific physiological and metabolic adaptations in order to improve performance. It is important to know what physiological and metabolic adaptations occur while at different intensities and how they can be improved in training. An endurance athlete should never stop training in zone 2. The ideal training plan should include 3-4 days a week of zone 2 training in the first 2-3 months of pre-season training, followed by 2-3 days a week as the season gets closer and 2 days of maintenance once the season is in full tilt.

There is a lot of guessing with the one-size-fits-all concept. Personalization and individualization is key. To achieve this individualization, physiological testing is the only manner to accurately be able to obtain the necessary information to tailor and personalize. This is very well known by top athletes and coaches but unfortunately most amateur athletes never get to know this necessary information because they never get tested.

Athletes should not be “shy” or intimidated to go to an exercise physiology lab and get tested. It just makes good sense!

Let's get started!

............................................... Test don't guess! #metabolicefficiency

[J Achten1, A E Jeukendrup]


bottom of page