Since its inception, breath analysis has been given many names, including metabolic testing, VO2max testing, Cardiopulmonary exercise testing, and cardio-metabolic analysis. These names are derived from their ability to analyze the three elemental mechanisms that participate in oxygen absorption, transfer, and utilization, namely, our lungs, heart, and cells.
In this article, we dive into the biomarkers breath analysis analyses and how they are translated into actionable evaluators of our health and performance.
The elemental metrics
The gold standard for analyzing human breath includes the measurement of oxygen concentration (O2), carbon dioxide concentration (CO2), and flow volume in real-time during inhalation and exhalation. The graph below shows how these three metrics evolve during inhalation and exhalation.
To better understand the sinus-like waveform of these signals, one needs to consider our body’s primary function, which is the absorption of air with high O2 content followed by exhalation of air with lower O2 content and higher CO2 generated by metabolic processes. The longer air stays within the lungs, the more O2 it transfers and the more CO2 it receives from the bloodstream. As a result, the deeper the inhaled air goes into the lungs, the more O2-CO2 exchange it experiences, leading to lower O2 and higher CO2 concentrations. This process is reflected in the signals picked up by the CO2 and O2 sensors. When the subject exhales, O2 concentration drops and CO2 concentration increases as air from the deeper parts of the lungs make it back to the mouth and nose during exhalation. When exhalation is followed by inhalation, the CO2 and O2 concentrations immediately revert back to concentrations the atmosphere around us contains, which are generally 20.9% for O2 and 0.05% for CO2.
Flow volume represents the rate at which air passes through your mouth and nose. During inhalation, air moves from the atmosphere and into your lungs. During exhalation, air moves in the exact opposite direction. This is reflected in the “flipping” of the curve above and below the x-axis.
Combining the O2 and CO2 concentration signals with flow volume breath analysis of twenty-three cardio-metabolic biomarkers that evaluate one’s health and performance.
- VO2peak: Maximum volume of oxygen consumed
- VCO2: Volume of carbon dioxide produced
- Respiratory Exchange Ratio (RER): Ratio of carbon dioxide volume produced over oxygen volume consumed.
- Tidal Volume (VT): Volume of air exhaled in one breath.
- Breathing Frequency (BF): Number of breaths completed in one minute.
- Minute Ventilation (VE): The volume of air exhaled in one minute.
- VE/VCO2: Ratio of minute ventilation over carbon dioxide volume produced.
- O2pulse: Ratio of oxygen volume consumed over heart rate.
- VO2/BF: Ration of oxygen volume consumed over breathing frequency.
- End-tidal CO2 (FetCO2): The highest concentration of carbon dioxide achieved during exhalation.
- End-tidal O2 (FetO2): The highest oxygen concentration achieved during inhalation.
- Fraction of expired CO2 (FeCO2): Average carbon dioxide concentration in one exhalation.
- Fraction of expired O2 (FeO2): Average oxygen concentration in one exhalation.
- Heart rate: Number of heartbeats per minute.
- Heart Rate Variability (HRV): The time variability between heartbeats
- Forced Expired Volume (FVC): The maximum volume of air exhaled at rest during the most prolonged exhalation possible.
- Caloric burn: Number of calories burned per minute.
- Fat oxidation: Grams and calories of fat burned per minute.
- Carbohydrate oxidation: Grams and calories of carbohydrate burned per minute.
- Mechanical Efficiency: Ratio of mechanical power over calorie burn per second.
- Crossover point: The heart rate at which carbohydrate and fat oxidation reach the same level.
- Aerobic Threshold or First Ventilatory Threshold (VT1): The heart rate at which fatigue accumulation begins at a sustainable rate for the body.
- Anaerobic Threshold of Second Ventilatory Threshold (VT2): The heart rate at which fatigue accumulation begins at an unsustainable rate for the body.
The following table provides an overview of how the cardio-metabolic variables measured by PNOĒ are divided based on the area of physiology they represent and affect.
Although the biomarkers described above provide some of the best indicators of a person’s cellular, metabolic, cardiovascular, and respiratory fitness, they are not easy-to-understand insights to the average person. This is why PNOĒ created ten metrics that describe the different elements evaluated by breath analysis. These include
- Metabolic rate
- Cardiovascular fitness
- Aerobic health
- Respiratory capacity
- Respiratory capability
- Respiratory coordination
- Expiratory power
- Recovery capacity
- Fat burn efficiency
- High-intensity performance
- Movement economy
- Breathing and cognition
- Breathing and posture
Definition of recovery capacity: This metric represents your ability to recover from physical exercise.
How it’s measured: Recovery Capacity is measured by assessing the rate with which your heart rate and volume of carbon dioxide exhaled (VCO2) drop during the recovery phase of your exercise test. The faster your heart rate and VCO2 drop the first few minutes of recovery, the higher your Recovery Capacity. A rapid drop in heart rate indicates that your cardiovascular and respiratory systems can recover quickly. A rapid drop in VCO2 indicates a speedy recovery of your cellular and metabolic system.
Why it’s important for your goal (P): Having a high Recovery Capacity is essential for every sport and especially for dynamic ones (e.g., basketball) where there is a continuous change between exercise bursts following recovery phases. The higher your Recovery Capacity, the greater your body’s ability to recover and the lower the fatigue it accumulates.
Why it’s important for your goal (W): Having a high Recovery Capacity is essential for any type of workout and especially for interval training (e.g., spinning) where there is a continuous change between exercise bursts following recovery phases. The higher your Recovery Capacity, the greater your body’s ability to recover, the longer you can exercise for, and the more calories you burn.
What it means: It’s a gauge of how fast or slow your metabolism is. In other words, whether your body is burning more or fewer calories than what’s predicted based on your weight, gender, age, and height.
How it’s measured: Metabolic Rate is calculated by assessing your Resting Metabolic Rate, the rate with which you burn calories at rest, and your Mechanical Efficiency during low exercise intensities, the rate with which you burn calories in the first stage of your exercise test. It’s important to note that your Mechanical Efficiency during medium and high exercise intensities is not indicative of how fast or slow your metabolism is and is therefore not considered when calculating this metric. As your Metabolic Rate slows, Mechanical Efficiency is typically the first of the two to change by increasing, indicating that your body burns fewer calories during daily activities (e.g., moving around the house) than predicted. A decrease in Resting Metabolic Rate typically follows as the metabolic slowdown becomes more severe, indicating that you are burning fewer calories to sustain vital functions (e.g., brain, heart, liver function) than predicted.
Why it’s important for your goal (P): A high Metabolic Rate (i.e., having both a high Resting Metabolic Rate and low mechanical efficiency ) indicates low levels of training fatigue accumulations. Reduction in Resting Metabolic Rate and/or increase in Mechanical Efficiency in low exercise intensities are highly correlated with unsustainable accumulation of exercise strain.
Why it’s important for your goal (W): A high Metabolic Rate will protect you from weight gain as your body will burn more calories allowing you to eat more without gaining weight. It also facilitates weight loss as burning more calories means that even a modest restriction in food intake will result in a meaningful calorie deficit and weight loss. A high Metabolic Rate is attained through a high Resting Metabolic Rate and a low Mechanical Efficiency in low exercise intensities.
What it means: It’s a gauge of how well your lungs and heart perform in high exercise intensities.
How it’s measured: High-intensity Performance is calculated by assessing how well your lungs oxygen and well your heart pumps it into your body during high exercise intensities (i.e., Zone 4 and Zone 5). This is reflected by two metrics namely, O2pulse, the oxygen pumped by heartbeat, and VO2/BF, the oxygen absorbed per breath cycle. The higher the volume of oxygen your heart pumps per heartbeat (i.e., O2pulse) and your lungs absorb per breathing cycle (i.e., VO2/BF), the greater your ability to perform well in high exercise intensities. A flattening or declining value in any of the two will immediately reduce your athletic performance.
Why it’s important for your goal (P): Having a high and continuously increasing O2pulse and VO2/BF throughout high exercise intensities will ensure that sufficient oxygen is delivered to your working muscles. This will in turn, ensure your body remains predominantly in an aerobic state when exercising in high intensities and therefore avoid fatigue buildup.
Why it’s important for your goal (W): Having a high and continuously increasing O2pulse and VO2/BF throughout high exercise intensities will ensure that sufficient oxygen is delivered to your working muscles. This will in turn, ensure your body remains predominantly in an aerobic state when exercising in high intensities allowing you to workout for longer in intensities where you burn the most calories.
What it means: It’s a gauge of how many calories you burn during exercise, in other words, whether your body burns more or fewer calories than what’s predicted based on your age, gender, and age.
How it’s measured: Movement Economy is measured by assessing the rate with which you burn calories in different exercise intensity levels also known as Mechanical Efficiency. A higher Movement Economy means your body burns fewer calories for a given level of exercise intensity (e.g., walking at 3 mph), whereas a lower Movement Economy means it burns more calories for the same exercise intensity compared to what’s predicted based on your age, gender, height, and weight.
Why it’s important for your goal (P): Having a high Movement Economy is valuable for all sports and especially for endurance sports. It ensures your body requires less energy to operate, results in reduced food intake during athletic events, and minimizes fatigue buildup.
Why it’s important for your goal (W): Staying lean or losing weight requires a low Movement Economy in low exercise intensity (e.g., walking lightly), or in other words having a low Mechanical Efficiency. In simple words, you want your body to be uneconomical and burn a high number of calories during your daily activities. Check your Metabolic Rate score for more information on how Mechanical Efficiency can impact your metabolism and your ability to lose weight.
Fat Burning Efficiency
What it means: It’s the gauge of your cells’ ability to use fat as a fuel source during exercise. Your cells primarily “burn” fats and carbohydrates to release the energy they contain and power your body’s movement. The higher your Fat-burning Efficiency, the more your cells will rely on fats as a fuel source. Fat-burning Efficiency is also one of the most vital indicators of cellular health.
How it’s measured: Fat-burning Efficiency is calculated based on your Crossover Point, the exercise intensity where your body transitions from burning primarily fats to burning mainly carbs. The higher the exercise intensity this transition occurs, the higher your Fat-burning Efficiency.
Crossover Point: It’s the exercise intensity where your body transitions from burning primarily fats to burning mainly carbs. It’s expressed in heart rate (e.g., 132 bpm) or power (e.g., 130 watts), depending on the metric used to benchmark exercise intensity.
Why it’s important for your goal (P): Fat is a fuel source that’s abundant and sustainable for your body. It’s abundant since the average person typically carries ~30,000 kcal worth of fat (vs. ~2,000 kcal worth of carbs) and sustainable because it doesn’t produce fatigue to the working muscles when used. Therefore, the higher your Fat-burning Efficiency, the higher your ability to exercise longer and harder.
Why it’s important for your goal (W): Fat is a fuel source that requires oxygen to be “burnt.” The more oxygen your cells can absorb and use, the healthier they are and the more they can rely on fat as a fuel source. That’s why Fat-burning Efficiency is one of the most powerful indicators of cellular health, a metric that’s strongly correlated with longevity and health.
Breathing and Stability
What it means: It’s a gauge of how your breathing affects your posture, likelihood of myoskeletal injury, and lower back pain.
How it’s measured: Breathing and Stability is calculated by assessing your Breathing Rate and Tidal Volume, the volume of air you exhale concerning your FEV1, and the maximum volume you can exhale. When you breathe too fast and shallow, your abdomen loses its stability, increasing the likelihood of bad posture, injuries during sport, or the development of long-term lower back pain. This happens when your Tidal Volume is a small fraction of your FEV1 while your Breathing Frequency is also high through the exercise test.
Why it’s important for your goal (P): Abnormal breathing patterns are critical contributors to myoskeletal injuries across all sports. Moreover, they directly reduce endurance sports performance by lowering movement economy and increasing the rate at which your body accumulates fatigue. Alleviating breathing abnormalities that destabilize your core is one of the easiest and most impactful wins in your training.
Why it’s important for your goal (W): Abnormal breathing patterns are the most significant risk factor for myoskeletal problems like lower back pain which currently represent the most significant burden to health systems and one of the most important factors reducing the quality of life. Correct breathing will vastly improve posture, feelings of myoskeletal pain, and quality of life.
Breathing and Cognition
What it means: It’s a gauge of how your breathing affects your brain function and ability to think.
How it’s measured: Breathing and Cognition is calculated by assessing your Breathing Frequency at rest as well as low levels of physical activity in combination with the amount of carbon dioxide you exhale per breathing cycle (i.e., VCO2). If you are breathing too fast (i.e., breathing frequency is high) while exhaling high volumes of carbon dioxide (e.g., VCO2 values are high), you enter a state known as hyperventilation. Hyperventilation reduces the carbon dioxide levels in your blood which in turn causes two phenomena to occur. First, arteries in your neck become narrower, reducing oxygen flow to your brain. Second, oxygen becomes more tightly bound to hemoglobin and becomes harder to transfer from the bloodstream into brain cells. Less oxygen delivered to your brain cells means lower cognitive capacity and reaction time.
Why it’s important for your goal (P): Hyperventilation during training reduces oxygen delivery to the brain almost immediately, causing you to react slower and respond less effectively to situations requiring rapid reflexes. Hyperventilation doesn’t only occur during high exercise intensities. More than 30% of athletes suffer from subtle breathing abnormalities in low to medium exercise intensities impacting their cognitive capacity during most of their athletic performance.
Why it’s important for your goal (W): Hyperventilation is considered one of the most common but underdiagnosed conditions that severely impact the quality of life in our society. It’s estimated that 15% of the population chronically hyperventilates, with only a handful knowing about it. Chronic hyperventilation reduces cognitive capacity at work, increases feelings of fatigue, and is associated with higher rates of anxiety and panic attacks.
Definition of respiratory capacity: It’s a gauge of how big your lungs are.
How it’s measured: Respiratory Capacity is calculated by assessing your FVC, the maximum volume of air you can breathe in, and FEV1, the maximum volume you can breathe out in one second. The higher these two values are the bigger your lung volume is.
Why it’s important for your goal (P): Oxygen is the most critical element of performance as it constitutes the necessary ingredient your body needs to burn nutrients and produce the energy it needs to move and function. The bigger your lungs, the more oxygen you can absorb, the more you can exercise for longer and more intensely.
Why it’s important for your goal (W): Oxygen is the most critical element for a long and healthy life as it constitutes the fundamental ingredient cells use to operate and thrive. The bigger your lungs, the more oxygen you can absorb and deliver to your cells.
What it means: It’s a gauge of how much of your lung volume you can use.
How it’s measured: Respiratory Capability is calculated by assessing your Tidal Volume, the volume of air you exhale in every breath cycle, and Breathing Frequency, the number of breaths you take every minute. Maintaining high Tidal Volume as Breathing Frequency increases indicates that you can use large parts of your lungs’ volume even as they expand and contract more and more rapidly. This will ensure a high Respiratory Capability score.
Why it’s important for your goal (P): Oxygen is the most critical element for athletic performance, and your lungs are one of the most vital organs in the oxygen delivery chain. When your lungs aren’t expanding and contracting enough, they operate less effectively as they absorb less oxygen-rich air and expel less carbon dioxide. This limits your overall oxygen absorption ability, limiting the amount of physical work your muscles can produce and expediting fatigue buildup.
Why it’s important for your goal (W): Oxygen is the most critical element for every cell in your body, and your lungs are one of the most vital organs in the oxygen delivery chain. When your lungs aren’t expanding and contracting enough, they operate less effectively as they absorb less oxygen-rich air and expel less carbon dioxide. This limits oxygen absorption and the oxygen available to your cells, leading to chronic fatigue, lower cognitive function, and reduced ability to workout.
What it means: It’s a gauge of whether your lungs have strength to fully contract during exhalation.
Why it’s important for your goal (W): Having lung muscles that are strong enough to effectively empty your lungs during exhalation is important for ensuring proper breathing function. Pushing enough air out during exhalation is necessary for clearing carbon dioxide effectively. When exhalation isn’t strong enough carbon dioxide may start to build up leading to feelings of fatigue, dizziness and even chronic disease such as COPD and cystic fibrosis.
Why it’s important for your goal (P)Strong exhalation is critical for athletic performance as clearing carbon dioxide is a key mechanism for removing fatigue metabolites from your body during exercise. When carbon dioxide isn’t effectively cleared fatigue buildup in the muscles starts almost immediately.
What it means: It’s a gauge of whether your breathing follows a normal pattern during training that’s not negatively impacting your posture, brain function, and muscle oxygenation.
Why it’s important for your goal (W): Irregular breathing patterns during training,also known as hyperventilation, will limit brain oxygenation and destabilize your core. Lower brain oxygenation causes feelings of dizziness and fatigue. A destabilized core elevates the risk of injuries such as lower back pain.
Why it’s important for your goal (P): Irregular breathing patterns during training, also known as hyperventilation, reduce carbon dioxide levels in the blood making it harder for oxygen to enter the cells of your working muscles. This in turn limits your ability to move as oxygen is the most important element for athletic performance.
What it means: It’s a gauge of your cardiovascular system’s ability to pump oxygen-rich blood to your body. Your cardiovascular system includes:
- Your heart.
- Blood vessels (i.e., arteries, veins).
- Blood (i.e., what flows within your arteries and veins).
How it’s measured: Cardiovascular Fitness is calculated by your VO2peak, the maximum amount of oxygen your body can absorb, and your O2pulse, the amount of oxygen your cardiovascular system delivers in every heartbeat. A high VO2peak combined with a constant increase in O2pulse as exercise intensity increases ensures a high Cardiovascular Fitness score.
Why it’s important for your goal (P): Your body needs oxygen to break down nutrients (e.g., fats, carbs, proteins) and power the movement you are asking it to do. When oxygen supply is disrupted or becomes insufficient based on the energy demands of your activity, your body will resort to Anaerobic Metabolism, a process that is unsustainable and produces fatigue. The cardiovascular system pumps oxygen to your cells and is thus a critical system in keeping your body moving sustainably.
Why it’s important for your goal (W): Cardiovascular disease is the number one cause of death and includes several life-threatening conditions such as ischemic heart disease (AKA Coronary Artery Disease), heart failure, and valvular disease. A low VO2peak score combined with a flattening or decline in O2pulse is considered a credible risk factor for them, one that can help you act early.
What It means: It’s a gauge of your overall health and provides the strongest predictor of how long and well you will live. It’s also one of the most vital indicators of athletic performance.
How it’s measured: Aerobic Health is calculated based on your VO2peak, the maximum amount of oxygen your body can absorb. The higher your VO2peak is, the higher your Aerobic Health. Since oxygen absorption requires effective operation of all critical organs, namely lungs, heart, cells, and blood, Aerobic Health provides the most holistic picture of every system essential to a long life and athletic performance.
Why it’s important for your goal (P): Your body needs oxygen to break down nutrients (e.g., fats, carbs, proteins) and power the movement you are asking it to do. When oxygen supply is disrupted or becomes insufficient based on the energy demands of your activity, your body will resort to Anaerobic Metabolism, a process that is unsustainable and produces fatigue. Hence, the more oxygen your body can absorb, the more movement it can produce without getting tired.
Why it’s important for your goal (W): Oxygen is the molecule of life. It’s the critical ingredient in your metabolism, the process by which your cells “burn” nutrients (e.g., fats, carbs, proteins) to release their energy and keep you alive and moving. Your heart, lungs, and cells all participate in this process. Whenever any of them breaks down, your Aerobic Health is immediately reduced. That’s why The American Heart Association has recognized it as the most holistic gauge of your overall health. It’s also no surprise that every significant chronic condition (i.e., heart, lung, metabolic) is related to these systems and is manifested when their ability to move or use oxygen is reduced.