VO₂max - the overlooked indicator of heart disease risk

Cardiorespiratory fitness (CRF), or cardiovascular exercise capacity, is the greatest predictor of overall health, endurance, and longevity. CRF measures your body’s ability to transport and use oxygen for energy during physical activity, from running a 5K to completing everyday errands. It is quantified by VO₂max, the gold standard metric to assess maximal oxygen consumption during intense exercise. This metric is invaluable for both athletes seeking performance improvements and individuals aiming to enhance their health. Decreased CRF is strongly associated with a higher risk of developing chronic health conditions, such as hypertension, type 2 diabetes, cancer, and premature death. Understanding and improving VO₂max can improve heart health, increase stamina, and lead to an overall longer, healthier life.

What is VO₂max?

VO₂, or oxygen consumption, is the measure of the volume (V) of oxygen (O₂) utilized by the body each minute to create cellular energy, expressed as milliliters of oxygen consumed per kilogram of weight per minute (ml/kg/min). Oxygen, essential for energy production, is transported from the lungs, through the blood, and to your organs and muscles. Carbon dioxide (CO₂) is the main byproduct of this process, exhaled out with each breath.

At rest, VO₂ is minimal as your body requires a low amount of energy to maintain basic physiological functions like breathing, circulation, and digestion. This is typically around 3.5 ml/kg/minute, also equal to 1 metabolic equivalent (MET), a measure of an activity’s intensity level and required energy expenditure. 

Any form of physical exertion – whether it’s sports, exercise, or daily activities like walking and climbing stairs – will increase the MET value and thus intensify the demand to fuel your muscles for motion. The body adjusts by increasing breathing rate, heart rate, heart contractility, and oxygen uptake by muscles.

VO₂max quantifies the maximum amount of oxygen your body can utilize per minute, representing the peak capacity. This metric serves as a key indicator of your cardiovascular and metabolic systems' efficiency, with normative values based on age and gender.

Why does VO₂max matter?

Cardiorespiratory fitness (CRF) is essentially a measure of how in shape your body is, assessing how efficiently the cardiovascular, respiratory, and metabolic systems work together to deliver blood and elevate oxygen consumption to match increased work demands by the body. A high VO₂max is correlated with better physical fitness and is associated with a lower risk for cardiovascular disease and increased longevity.

A higher VO₂max predicts:

  • Enhanced Athletic Performance and Stamina: Higher VO₂max values correlates with increased ability to sustain intense activity and recover more quickly. This is especially valuable to boost performance for endurance-based athletes but also extends beyond sports to support everyday tasks by reducing fatigue and helping maintain energy throughout the day. 

  • Stronger Heart Health: VO₂max improvements reflect better cardiac function to maintain adequate blood circulation. This indicates improved cardiac output, myocardial contractility, and endothelial function, all greatly reducing the risk of cardiovascular disease (CVD).

  • Better Metabolic Activity: A rise in MET levels corresponds with greater caloric expenditure. Improved exercise capacity allows individuals to sustain greater calorie burn and fat oxidation during workouts, aiding in weight management. Additionally, it boosts resting metabolic rate (RMR), allowing the body to burn more calories even at rest. 

  • Longer Life Expectancy: Men and women with greater CRF are associated with 47% and 70% lower risk of cardiovascular disease (CVD) mortality, and 43% and 53% lower risk for all-cause mortality, respectively, when compared to those with lower CRF. 

How is VO₂max measured?

Measuring VO₂max provides valuable insights into your body’s ability to handle physical exertion, helping to pinpoint areas for improvement and guide personalized fitness and health goals, whether for athletic performance or long-term well-being.

VO₂max testing methods range from clinical-grade accuracy to practical, everyday solutions:

  • Cardiopulmonary Exercise Stress Testing (CPET): The most accurate and direct measurement of VO₂max, conducted in controlled clinical or sports settings through maximal exercise combined with gas analysis. It is the test of choice here at Whole Heart Cardiology. 

  • Submaximal and Field Tests: VO₂max can be estimated using submaximal and field tests, which rely on heart rate responses or time to completion of exercises performed at lower intensities in various settings. These are practical, cost-effective assessments ideal for individuals who may not tolerate maximal exertion due to age, injury, or other limitations, though they are generally less precise. Common examples include the Astrand-Rhyming Cycle Test, Bruce Protocol Treadmill Test, PACER shuttle run, Chester Step Test, Cooper 12-minute run, and 1-mile walk test.

  • Wearable Devices: Numerous smartwatches, chest straps, and arm bands use heart rate and activity data to estimate VO₂max, offering convenient, real-time insights. Many also calculate METs during workouts, providing another view of energy output. While research is still ongoing to validate their accuracy, they offer an easy and accessible way to get a general VO₂max estimate and track progress over time.

What factors affect VO2max?

Low VO₂max values suggest reduced fitness capacity, however, other factors including age, gender, and genetics also affect your VO₂max.

  • Genetics: Hereditary traits account for as much as 50% of VO₂max variability. Some individuals are genetically predisposed to greater lung capacity, stronger cardiovascular systems, and muscle compositions better suited for endurance. However, the specific genetic causes influencing CRF still remain unclear.

  • Age and Gender: VO2max generally peaks in our 20s and declines by approximately 10% each decade thereafter. On average, men tend to have about 10% higher values than women, primarily due to physiological differences such as greater muscle mass, larger heart and lung sizes, and higher total hemoglobin levels.

  • Lifestyle Habits: Other than regular physical activity, proper sleep and avoiding smoking or excessive alcohol consumption impact VO2max.

  • Body Composition:  While studies show body fat percentage does not have direct effects on VO₂max, higher fat levels can lower VO₂max indirectly. Excess fat mass increases the workload on the body to supply oxygen, making aerobic efficiency more challenging.

  • Training Altitude: Living or training at higher altitudes can boost oxygen efficiency over time.

How to improve your VO₂max?

Despite some nonmodifiable factors, physical activity is the most controllable variable for improving VO₂max. Engaging in continuous exercise or higher MET activities can enhance VO₂max and slow its natural decline, regardless of age or background.

Even small improvements in CRF can have significant health benefits. Increasing CRF by just 1 MET (3.5 ml/kg/minute) is associated with 15% reduction in all-cause mortality and a 19% reduction in cardiovascular mortality. 

The American Heart Association (AHA) recommends aiming for at least 150 minutes (2.5 hours) of moderate-intensity or 75 minutes of vigorous-intensity aerobic exercise each week to maintain good CRF and boost your VO₂max.

Here are some effective ways you can achieve this:

  1. Continuous Training - Incorporate sustained moderate-to-high intensity aerobic activities, such as: 

    • Running or cycling at 70-85% of your maximum heart rate for 30-60 minutes

    • Swimming or rowing for extended durations to build endurance

  2. High-Intensity Interval Training (HIIT) - Alternating short bursts of high-intensity exercise with recovery periods. HIIT has been shown to be more effective than continuous moderate-intensity aerobic exercise in improving VO₂max largely due to the repeated bouts of intense effort, which place greater demands on the cardiovascular and muscular systems, leading to more pronounced adaptations in oxygen delivery and utilization in a shorter time duration. Examples include:

    • Sprint for 30 seconds, followed by 1-2 minutes of walking

    • Cycling intervals of intense pedaling for 1-2 minutes, followed by 2-3 minutes of recovery

Resistance Training - While it may not directly increase VO₂max, strength training improves muscle efficiency and oxygen utilization. Include exercises like squats, deadlifts, and bench presses for overall fitness gains.

Closing Thoughts

Prioritizing VO₂max improvement is a key step toward better fitness, cardiovascular health, and longevity. Whether through consistent aerobic exercise, interval training, or resistance workouts, small but sustained efforts can yield profound benefits. For those who are sedentary or just getting started, focusing on increasing moderate to vigorous continuous exercise on most days of the week is an effective first step, while those who have been at it for awhile may benefit from incorporating structured HIIT protocols to push their VO₂max and endurance performance further. By boosting your body’s capacity to use oxygen efficiently, you’re investing in a longer, healthier, and more active life.

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