Cardio-Metabolic Analysis with PNOĒ Leave a comment

PNOE AthletesBy Panos Papadiamantis and Apostolos AtsalakisHave you ever wondered why one of the most holistic assessments of human physiology is currently restricted to a handful of sports science labs, hospitals, and research centers? I’m referring to cardio-metabolic analysis, the only known non-invasive method capable of analyzing how a person’s cardiovascular, pulmonary, and metabolic systems operate both individually and in unison1. Due to its ability to accurately assess the energy consumption and substrate utilization of the human body (i.e., percentage contribution of fats and carbohydrates in the human body), cardio-metabolic analysis has long been considered the gold standard assessment for developing physical exercise and nutritional programs2. However, despite its well-established value in performance optimization, very few athletes and coaches are aware of its benefits and even fewer use it in their training.

Cardio-metabolic analysis is the best assessment to develop physical exercise & nutritional programs.CLICK TO TWEETBut why is it that such a holistic and foundational assessment remains so inaccessible3? The reason is due to cost-prohibitive devices with cumbersome operation processes, the time requirements to conduct a cardio-metabolic test, the discomfort caused by the headgear of traditional metabolic analyzers, and the immobile nature of existing solutions that are unable to collect data from real-life training conditions4. These are enough complications to make even the most data-driven coach contemplate whether or not to prescribe the test, and to make the average athlete dread the thought of going through it. Specifically:

  • A medical grade cardio-metabolic analyzer costs more than $30K and requires specialized training to operate.
  • Interpretation of the data generated from such a device and the development of physical exercise and nutritional regiments based on the information gathered requires a degree in exercise physiology, as well as experience from tens (if not hundreds) of tests.
  • Running a test (including the syringe calibration of the flow sensor) and crunching the data can take up to one hour.
  • The immobility of most devices—and the unreliability and fragility of the few portable options that exist—have made real-life cardio-metabolic testing unrealistic, therefore restricting it to the lab. As a result, the substantial differences in an athlete’s physiological response between the lab and real-life training conditions have also led many coaches to distrust many of the insights of indoor cardio-metabolic testing and resort to less sophisticated but outdoor-based forms of assessment.
  • The discomfort most mouthpieces inflict on test subjects has led athletes to develop an aversion towards the assessment and coaches to be skeptical about prescribing it.

Consequently, the lack of a convenient and cost-effective solution results in the average team resorting to unreliable assessment methods for prescribing training and nutrition.

What Is Cardio-Metabolic Analysis?

Cardio-metabolic testing, also known as VO2max testing, ergospirometry, cardiopulmonary exercise testing, or metabolic testing, is largely misunderstood and underutilized. The sheer number of names is silent proof of how fragmented and limited its utilization is, and speaks to the mystery around the metrics. The clear definition of cardio-metabolic testing is the measurement of the oxygen uptake (VO2), carbon dioxide production (VCO2), and ventilation (VE—total air volume exchanged with the environment) of a person through the continuous analysis of his inspiratory and expiratory gases5. By combining these three basic cardio-metabolic parameters, as well as those used to derive them, we can assess the cardiopulmonary response of an individual and his energy consumption (i.e., number of kcal expended in a period of time), and determine the contribution of the two major fuel sources (i.e., carbohydrates and fats) in his energy mix.

Overall, cardio-metabolic analysis has not only been restricted to very few sophisticated and well-funded athletic organizations, but the interpretation of the information it generates has also been superficial. Not only are coaches and teams avoiding cardio-metabolic analysis, but the very few who do apply it underutilize the data it can offer3. However, recent technological advancements in sensing technology have managed to overcome the obstacles posed by existing devices and are bringing cardio-metabolic analysis to the core of athletic training. The following case study describes how PNOĒ—the world’s first portable, low-cost, and medical-grade cardio-metabolic analyzer—has managed to make the most insightful and advanced assessment accessible to a football academy in Athens, Greece.

Energy Efficiency: The Mother of All Metrics

A famous football (soccer) team based in Athens, Greece, has utilized cardio-metabolic analysis to evaluate its players while playing on the pitch. The affordability and robustness of PNOĒ allowed the coach to concurrently assess a group of athletes playing the sport and measure their fuel efficiency and substrate utilization during real-life training scenarios. They measured fuel efficiency by combining data from PNOĒ, which provided information on the metabolic cost of the physical activity performed (i.e., the chemical energy consumed) and a power meter, which provided the amount of mechanical work generated.

By calculating the ratio of mechanical over metabolic power, the coach was able to derive the amount of chemical power converted to useful mechanical propulsion: or, in other words, the gross fuel efficiency of his athletes6. Substrate utilization was also measured directly through PNOĒ through the respiratory exchange ratio (RER)—the gold standard metric for measuring the contribution of fats and carbohydrates to each individual athlete’s energy mix7.

Fuel efficiency stands out as the most central metric, as it is directly associated with most key elements of an athlete’s performance, including fatigue, fitness level, technique, mobility during the game, etc. For instance, fatigue accumulation, and the concomitant loss of motor control, or low fitness levels constitute factors that lead to higher metabolic costs for the same mechanical power generation (i.e., same body movement), resulting in reduced efficiency.

Fatigue is generally defined by two conditions:

  1. an inability to maintain the target mechanical power; and
  2. a decrease in muscular performance and efficiency while maintaining the same amount of power output.

While a) can be easily monitored (i.e., measurement of pace, power output, etc.), b) can only be assessed with the direct measurement of fuel efficiency. Moreover, since it’s not easily assessed, b) can prove to be one of the most dangerous drivers of fatigue accumulation and, as a result, a major driver of sport injuries.

The general mechanisms correlating reduction in fuel efficiency—i.e., increase in metabolic cost for the generation of the same mechanical power output—and the occurrence of injuries are:

  1. progressive motor recruitment (i.e., impairment of Type I muscle fibers and the progressive recruitment of energetically less efficient Type II muscle fibers);
  2. progressive loss of motor control; and
  3. compensatory response of surrounding muscles; all of which are directly linked to injury occurrence while directly and nearly instantly impacting the fuel efficiency of an athlete8,9.

Therefore, by measuring fuel efficiency in real-life conditions in specific time intervals (e.g., every two weeks) or after important events (e.g., after a game or a week of intense training), a coach is able to collectively monitor the fatigue accumulation of his team.

Substrate utilization revealed the movements and exercise intensity levels at which each athlete’s metabolic condition shifted predominantly from fat to carbohydrate oxidation. To understand the importance of this phenomenon, we must look into the basic mechanisms according to which our body’s fuel sources are utilized. Our body relies primarily on a mixture of fat and carbohydrates to power its energy needs. Fat, a fuel source oxidized through an aerobic process (i.e., a chemical reaction that involves O2), is usually the predominant energy source during light and medium exercise intensities. Carbohydrates, on the other hand, are a fuel source that can be oxidized by both aerobic and anaerobic processes (i.e., a chemical reaction that doesn’t involve O2), and are usually the predominant energy source during higher-intensity exercises.

Aerobic metabolism does not generate any fatigue, but it evolves slowly and cannot immediately cover the entire energy demands of an exercise. On the contrary, anaerobic metabolism can be very rapidly initiated to cover energy demands, but generates fatigue. Therefore, aerobic metabolism is the predominant energy mechanism during light and medium-intensity workouts or steady state exercises, whereas anaerobic metabolism is the predominant energy mechanism during high-intensity workouts, or when exercise intensity changes (in other words, during the transient phase from a lower to a higher intensity exercise state during which aerobic metabolism has not yet been able to “catch up” with energy demands). Therefore, the ability to rapidly engage aerobic metabolism in response to an increase in energy demands and develop it such that it can cover high levels of energy demand is the ultimate goal of most athletes. This is what we refer to as a “strong” aerobic base.

Returning to our Greek football team, the direct measurement of carbohydrate and fat oxidation—and, consequently, the interplay between aerobic and anaerobic metabolism—provided for the first time the ability to measure real-time fatigue accumulation, as well as how aerobically “fit” each player is. And, all of this executed within the conditions and movements they are regularly exposed to.

Lastly, the combination of fuel efficiency and substrate utilization can be used to accurately assess the nutritional requirements of an athlete. Specifically, by monitoring energy expenditure (i.e., kcal/min) and substrate utilization (i.e., contribution of carbohydrates and fats to energy mix) through gas exchange, an athlete’s diet can be precisely formulated to achieve a specific weight goal or induce a desirable metabolic adaptation (i.e., make the athlete a more efficient fat burner). This is possible by establishing a correlation between the athlete’s mechanical power output (measured through motion sensors) and cardio-metabolic profile (measured through gas exchange analysis).


Following a number of assessments utilizing a cardio-metabolic analyzer and a power meter, the athlete’s energy expenditure profile (kcal/min) can be strongly correlated against biometrics such as mechanical power output and/or heart rate that can be gathered throughout their entire training session or even the entire day. As a result, by monitoring mechanical power output and/or heart rate, a coach or performance specialist can reliably and non-invasively “recreate” the athlete’s metabolic response and therefore derive their nutritional needs10,11.

Results and Interpretation

The assessment consisted of two 15-minute sessions during which a small group of European football players wore PNOĒ masks and played. In between the assessment sessions, the players underwent a two-hour training session. The PNOĒ online platform allowed the collective analysis of cardio-metabolic and biomechanical information for the calculation of fuel efficiency and substrate utilization.

PNOE Cones
Image 1. By monitoring mechanical power output and/or heart rate, a coach or performance specialist can reliably and non-invasively “recreate” the athlete’s metabolic response and therefore derive their nutritional needs (10,11).

For each athlete, fuel efficiency and substrate utilization was compared between the two assessments in time intervals where levels of mechanical power output were comparable—i.e., power was used as a benchmark for intensity. The analysis was conducted on the PNOĒ online platform, where biomechanical and cardio-metabolic data were collectively analyzed in order to quantify the level of fatigue accumulation based on fuel efficiency and substrate utilization. Analysis of the data revealed the following insights:

  • Players with higher contribution of carbohydrates in their metabolic activity during the first assessment incurred a higher reduction in fuel efficiency between the two assessments.
  • Players with lower fuel efficiency during the first assessment were able to maintain lower mechanical power outputs during the second assessment.
  • Players with high fuel efficiency had higher contribution of fats in their metabolic activity (i.e., a greater portion of their energy consumption was covered through fat oxidation) and were able to maintain higher levels of mechanical power output during the second assessment.

Repeating the same assessment protocol can reveal how different training routines induce changes in fatigue accumulation among players. Moreover, creating a baseline assessment protocol consisting of two 15-minute assessments and a two-hour training session in between allows for the quantification of fatigue accumulation during a tournament or intense training season. Specifically, the repetition of the baseline assessment protocol before and after the tournament or intense training season should reveal the level of fatigue each player has incurred in their cardio-metabolic system.

Why Measure in Real-Life Conditions?

The traditional method of assessing the cardio-metabolic condition of an individual is through a standardized protocol of increasing intensity on a form of cardio equipment (i.e., treadmill or cycle ergometer). Although the benefits of standardization allow for easier comparison between tests, the drawbacks mentioned below have led many professionals to question the validity of indoor testing:

  1. Many athletes are not used to running on the treadmill or cycling on a stationary bicycle. As a result, the inability to move freely and naturally gives a distorted picture of cardio-metabolic data, prevents subjects from reaching high-intensity exercise states, and, in some cases, can even cause injuries.
  2. Movement and, by implication, muscle engagement during an actual sport (i.e., in the case of football, repeated alteration between different running speeds and directions) can be substantially different compared to a treadmill or stationary bicycle, leading to substantially different levels of energy expenditure and substrate utilization.
  3. Environmental conditions such as temperature, wind, and humidity can affect a person’s cardio-metabolic state substantially, rendering the controlled lab conditions misleading.
PNOE Academy Soccer
Image 2. Before the PNOĒ mask, athletes often found the headgear of traditional metabolic analyzers uncomfortable, thereby developing an aversion towards the assessment itself. The PNOĒ is lightweight and mobile, shown here with Greek youth academy players.

About PNOĒ

PNOĒ has addressed the limitations posed by traditional cardio-metabolic analyzers by creating the first portable, low-cost, affordable, and medical-grade cardio-metabolic analyzer. Its key advantages are:

  • Requires no cumbersome calibration—for those who have experience with cardio-metabolic analyzers, PNOĒ doesn’t require the notorious 3-liter calibration syringe.
  • Begins measuring in less than three minutes and is fully operated through a smartphone that projects real-time cardio-metabolic data.
  • One-hundred percent cloud connected and transmits real-time cardio-metabolic data to the PNOĒ online platform, which can be accessed from anywhere around the world.
  • Accuracy has been validated against clinical gold standard metabolic analyzers.
  • Can be used in the field to assess athletes in the sport and environment they train in, to provide training recommendations that are sport- and environment-specific.

Several high-profile fitness centers, sports teams, and research groups around the world currently use PNOĒ, and its advantages are effectively addressing the problems that have kept cardio-metabolic analysis confined. Athletes and coaches who implement PNOĒ in their training regimens and take cardio-metabolic analysis into real training conditions are now gaining access to a wide spectrum of unique insights and metrics, and reporting substantial changes in performance. From our vantage point, PNOĒ has achieved two big wins: 1) it made cardio-metabolic analysis accessible to the average athlete; and 2) it made cardio-metabolic analysis sport- and environment-specific, consequently rendering its insights directly applicable and far more impactful.


Cardio-metabolic analysis constitutes the most foundational assessment of human physiology. Its metrics provide unique insights into an athlete’s fitness and allow for targeted decision-making regarding their nutrition and training program. Decades of research have amassed unequivocal evidence indicating the breadth of information a single 15-minute cardio-metabolic test can reveal and point to the necessity of this type of assessment—not just for athletes, but also for the general population.

2016 was a landmark year for cardio-metabolic testing, with the American Heart Association elevating VO2peak to a vital sign and calling for its wide adoption in everyone’s health checkup12. Acknowledging the value that cardio-metabolic testing brings to the world of sports and public health, PNOĒ is helping to remove the operational barriers that have kept this assessment restricted to the lab for so many years and is now making it accessible, not only to the everyday athlete, but soon to the general population as well.

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