Why VO₂ Max Is Your Most Important Vital Sign — Part I

What It Is, Why It Matters, and How We Measure It

Most people can quote their cholesterol or blood pressure. Almost no one knows their VO₂ max—the single best snapshot of how well your heart, lungs, blood, liver, and every working muscle talk to each other. That needs to change.

My first VO₂ max test came late—spring of senior year in college at Texas Tech. Seeing the number (and everything it implied about performance and health) lit a fire. If I’d done that test as a freshman, I probably would have majored in exercise physiology. Instead, I’ve spent the last two decades in medicine—rummaging back and forth through specialties—only to arrive at the same conclusion: cardiorespiratory fitness (CRF) is the totality of the human engine. Heart, lungs, liver, muscle. One number that reflects how well it all works—especially when asked to go hard.

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What exactly is VO₂ max?

VO₂ max is the highest rate at which your body can:

• Extract oxygen from the air (pulmonary ventilation),

• Transport it via the bloodstream (cardiac output + hemoglobin),

• And utilize it in your working muscles (mitochondria + enzymes).

It’s typically expressed in either mL·kg⁻¹·min⁻¹ (relative, per kilogram body weight) or L·min⁻¹ (absolute, especially for larger athletes). If the test includes a clear plateau at maximal effort, it's a true VO₂ max. Otherwise, we refer to it as peak VO₂—a practical term used in most clinical settings.

What makes VO₂ max such a powerful “magnifying glass” into the human body is its integration of multiple systems: lungs, heart, blood, liver, skeletal muscle, capillaries, mitochondria, enzymes, and the autonomic and somatic nervous systems. VO₂ max is the limit of your engine’s capacity—the edge of what your body can sustain before it begins to fail or shut down.

You don’t just improve VO₂ max for a number—you improve how your body works.

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VO₂ Max vs. Traditional Vital Signs

At rest, your body needs only ~3.5 mL·kg⁻¹·min⁻¹ of oxygen (about 1 MET) to function—enough to lie in bed or sit quietly. For a 70 kg (154 lb) person, that’s just 245 mL/min—about ⅔ of a soda can.

But when you’re asked to perform—carry groceries upstairs, run a hill, climb a mountain—the difference between 14 and 50 mL·kg⁻¹·min⁻¹ is life-changing.

• Median VO₂ max for a healthy 45-year-old male: ~38–42 mL·kg⁻¹·min⁻¹

• Elite endurance athletes: >85 mL·kg⁻¹·min⁻¹

• World record: 97.5 mL/kg/min (Oskar Svendsen, 2012, age 18, cyclist)¹

• Alaskan sled dogs: ~240 mL/kg/min

• Pronghorn antelope: estimated ~300 mL/kg/min²
  

In contrast, patients with heart failure moving towards needing heart transplantation often have VO₂ max values <12–14 mL/kg/min^3,4.

Every 1-MET increase (~3.5 mL/kg/min) in CRF is associated with a 13% reduction in all-cause mortality⁵.

In a 2018 treadmill study of over 122,000 adults, elite fitness was the strongest predictor of survival—even after adjusting for diabetes, smoking, and coronary artery disease⁶.

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VO₂ Max Across the Lifespan

VO₂ max declines ~5–10% per decade after age 30 and accelerates after age 50 to ~10-20% per decade. But with consistent training, this can be slowed to ~ 3-5% per decade, stabilized, or even reversed. Here's a validated reference table based on treadmill CPET testing from the FRIEND Registry^7,8:

VO₂ Max Reference Ranges (FRIEND Registry, mL·kg⁻¹·min⁻¹)

*VO₂ max norms beyond age 79 are not well-validated. In older adults, individual performance, independence, and function may offer more useful insight than population-based percentiles.

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How is VO₂ Max Measured?

Smartwatch reliability:

• Garmin Fenix / Firstbeat: ~±3 mL/kg/min error⁹

• Apple Watch Series 7: ~4.5 mL/kg/min underestimation¹⁰

For accuracy, I retest using a metabolic cart every 6–12 months based on training or health goals.

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Why Isn’t VO₂ Max Measured More Often?

Historically, graded treadmill testing was standard practice. But over time, clinical focus has shifted toward:

• Imaging studies,

• Medication management,

• Easily tracked metrics (BP, lipids).

VO₂ max testing requires specialized equipment, trained staff, and a maximal-effort mindset. However, adverse event rates are <1 in 10,000 when done safely and following appropriate guidelines and protocols¹¹.

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What You Can Do Today

• Estimate your VO₂ max with your watch or a field test.

• Confirm with formal testing if you’re training seriously or managing illness.

• Track it every 3–6 months—treat a sustained drop like a warning sign.

• Ask your clinician to record VO₂ max in your medical chart—alongside BP and cholesterol.

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You now know what VO₂ max is, why it matters, and how to measure it.

In Part II—“Raising the Number: Turning VO₂ Max into Action”—I’ll share training protocols, zone breakdowns, and realistic improvement targets.

“Train for life. Think like an athlete. Live 20+ more years you actually want.”

Subscribe, share, and let’s move the needle.

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References

1. Wilson, Andrew. What the highest-ever VO₂ max tells us about genetics and cycling success. VeloNews, December 13, 2022. https://velo.outsideonline.com/road/road-training/what-the-highest-ever-vo2max-tells-us-about-genetics-and-cycling-success

2. Lindstedt SL, Hokanson J, Wells D, et al. Running energetics in the pronghorn antelope. Nature. 1991;353:748–750.

3. Weber KT, Janicki JS. Cardiopulmonary exercise testing for evaluation of chronic cardiac failure. Am J Cardiol. 1985;55(2):22A–31A.

4. Stevenson LW et al. Practical use of peak oxygen consumption in selection of patients for cardiac transplantation. Circulation. 1990;81(1):IV-31–38.

5. Kodama S, Saito K, Tanaka S, et al. Cardiorespiratory fitness and all-cause mortality. JAMA. 2009;301(19):2024–2035.

6. Mandsager K, Harb S, Cremer P, et al. CRF and long-term mortality. JAMA Netw Open. 2018;1(6):e183605.

7. Kaminsky LA, Arena R, Myers J, et al. Reference Standards from the FRIEND Registry. Mayo Clin Proc. 2015;90(11):1515–1523.

8. ​​Fitzgerald, M. D., Tanaka, H., Tran, Z. V., & Seals, D. R. (1997). Age-related declines in maximal aerobic capacity in regularly exercising vs. sedentary women: a meta-analysis. Journal of Applied Physiology, 83(1), 160–165.

9. Firstbeat Technologies. Fitness Level (VO₂ max) Estimation White Paper. 2017.

10. Lambe R, O’Grady B, Baldwin M, Doherty C. Apple Watch VO₂ Max Validation. PLoS One. 2025;20(5):e0323741.

11. American College of Sports Medicine. ACSM Guidelines for Exercise Testing and Prescription, 10th ed.

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