Is it more useful than heart rate, steps, or strength? Yes. But here’s the nuance.
Everyone’s tracking something.
Steps. Sleep. HRV. Calories. Heart rate zones. Readiness scores.
The noise is endless. The clarity? Rare.
So what should you track? What actually matters?
That depends on what you’re after.
If you want to know how hard you worked, wearables work.
If you want to know how well you’re recovering, HRV helps.
But if you want to know how long and how well you’ll live—start with VO₂ Max.
Let’s break down how it compares to other popular metrics—and when it makes sense to combine them.
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VO₂ Max vs. Resting Heart Rate: Ceiling vs. Idle
Resting heart rate (RHR) is the number of times your heart beats per minute while fully at rest—typically measured during sleep.
It’s easy to track and inversely related to aerobic fitness.
Lower = generally better.
But RHR is highly reactive. It jumps with stress, caffeine, alcohol, poor sleep, illness, even room temperature.
VO₂ Max, on the other hand, changes slowly—and only through sustained aerobic adaptation. It’s harder to manipulate, and that’s a feature, not a bug.
RHR shows how calm your engine is at idle
VO₂ Max shows how powerful your engine is at redline
Guess which matters more when life demands performance?
VO₂ Max vs. METs: The Misunderstood Conversion
You may have seen the term METs—especially on treadmill reports or cardiac rehab paperwork.
MET stands for Metabolic Equivalent of Task.
1 MET = the estimated amount of oxygen your body uses at rest.
By definition: 1 MET = 3.5 ml/kg/min of VO₂
So if your VO₂ Max is 35 ml/kg/min, you’re said to have a capacity of 10 METs.
Helpful? Somewhat.
But METs are population-based estimates, not personal measures. They assume a resting VO₂ of 3.5 across all people. And they’re often inferred without gas exchange, meaning the number may not reflect your actual physiological reality.
Bottom line: METs are a ballpark.
VO₂ Max is the scan.
VO₂ Max vs. Wearable Estimates: Directional, Not Diagnostic
Most people reading this may already have a “VO₂ Max number.”
It’s tucked into your Apple Watch, Garmin, Whoop, or Oura.
It updates automatically. It moves up or down. And it likely feels scientific.
But here’s the thing: it’s not actually VO₂ Max.
Wearables don’t measure oxygen consumption or carbon dioxide production.
They estimate fitness using heart rate during submaximal exercise—usually walking or running—and compare that to population models based on age, pace, and recovery patterns.
What you get is:
A prediction, not a measurement
Often 15–30% off from lab-tested VO₂ Max values—especially in highly fit or undertrained individuals [1]
Sensitive to altitude, illness, sleep, hydration, stress, and even temperature
It’s like estimating the structural integrity of a building based on how the windows rattle in the wind. You might be close—but you don’t really know.
The Wearable Reality
Wearables may be useful.
If they keep you moving more than you otherwise would, encourage smarter rest, or create awareness around long-term trends, they’re likely directionally helpful.
But if you’re using the number to:
Set your training thresholds
Evaluate longevity risk
Track aerobic progress over time
Compare yourself to a population or peer group
…you’ll need something more precise.
True VO₂ Max is measured, not inferred.
It requires a ramped effort protocol, gas exchange analysis, and trained supervision. It reflects not just your heart and lungs, but how well your blood, cells, and mitochondria actually use oxygen under maximum load.
So if your watch says 42 and your friend’s says 39—and you both feel equally fit—who’s right?
Possibly neither.
But if those numbers got you off the couch, outside in sunlight, and doing hard things again… they’ve served a purpose.
Just don’t confuse the estimate for the engine.
If you want to know where you really stand—test it.
VO₂ Max vs. Strength and Power: Two Types of Reserve
Strength is your ability to generate force.
VO₂ Max is your ability to sustain oxygen-powered output over time.
They’re not in competition—they’re complementary.
Strength protects against falls, fractures, and metabolic decline.
VO₂ Max protects against cardiovascular disease, fatigue, and functional decay.
In aging populations, both are powerful mortality predictors.
But where VO₂ Max reflects systemic integration, strength reflects neuromuscular reserve.
Think of it this way:
VO₂ Max = how far you can go
Strength = how much you can carry
Longevity favors both.
VO₂ Max vs. Step Count and Calorie Burn: Quantity ≠ Capacity
Most wearables are built to count:
Steps
Calories
Active minutes
But steps don’t guarantee intensity, and calorie estimates vary wildly based on algorithms, not actual exertion.
You can hit 10,000 steps a day and still have a dangerously low VO₂ Max.
You can burn 700 calories in a workout and see zero mitochondrial adaptation.
That’s because these metrics track movement, not capacity.
Steps = motion
Calories = estimate
VO₂ Max = adaptation
Only one of these reflects a deep biological shift.
VO₂ Max vs. HRV: Engine vs. Gearbox
Heart Rate Variability (HRV) measures the tiny variations in time between each heartbeat. Higher HRV generally signals a more adaptive nervous system.
Here’s how it works:
When your body is stressed, your sympathetic nervous system dominates → HRV drops
When your body is recovered, parasympathetic tone rises → HRV increases
A high HRV = flexibility.
A low HRV = rigidity—often associated with chronic stress, burnout, or illness [2].
VO₂ Max tells you what you can do under load.
HRV tells you how well you recover between loads.
They work together.
VO₂ Max = cardiovascular and metabolic horsepower
HRV = nervous system control and resilience
Which Metrics Actually Predict Mortality?
Let’s draw the line between what’s popular and what’s predictive:
VO₂ Max – strongest known predictor of cardiovascular and all-cause mortality [3]
Visceral fat – silent driver of inflammation and chronic disease [4]
Muscle mass and quality – critical for metabolic health and longevity [5]
Bone density – fracture resistance and independence, especially post-50 [6]
Strength – mobility, insulin sensitivity, fall prevention [7]
HRV – recovery readiness, adaptability, and all-cause mortality [2]
Gait speed – functional independence predictor [8]
Others—like step count, calorie burn, or sleep score—can be helpful when contextualized, but they don’t hold predictive power on their own.
The Real Picture: Triangulate with Precision
At DexaFit, we don’t guess.
We measure what matters—and use that to build your personalized healthspan blueprint.
Core Diagnostics (Predictive):
Complementary Metrics (Contextual):
This isn’t fitness vanity.
It’s clinically grounded data—designed to track capacity, resilience, and aging trajectory.
Want to build your true physiological profile?
Start with the most predictive metric of them all.
Book your VO₂ Max test with DexaFit.
References
Clausen JSR, Marott JL, Holtermann A, et al. Accuracy of heart rate-based VO₂ max estimation from consumer wearables: Validation against direct measurement. Eur J Prev Cardiol. 2021;28(15):1689–1699. doi:10.1177/2047487320919952
Jarczok MN, Koenig J, Mauss D, et al. The association of heart rate variability with all-cause mortality: a meta-analysis. PLoS One. 2014;9(12):e115003. doi:10.1371/journal.pone.0115003
Mandsager K, Harb S, Cremer P, et al. Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Netw Open. 2018;1(6):e183605. doi:10.1001/jamanetworkopen.2018.3605
Britton KA, Massaro JM, Murabito JM, et al. Body fat distribution, incident cardiovascular disease, cancer, and all-cause mortality. J Am Coll Cardiol. 2013;62(10):921–925. doi:10.1016/j.jacc.2013.06.027
Srikanthan P, Karlamangla AS. Muscle mass index as a predictor of longevity in older adults. Am J Med. 2014;127(6):547–553. doi:10.1016/j.amjmed.2014.02.007
Looker AC, Melton LJ, Harris TB, et al. Prevalence and trends in low femur bone density among older US adults. J Bone Miner Res. 2010;25(1):64–71. doi:10.1359/jbmr.090706
Rantanen T, Volpato S, Ferrucci L, et al. Handgrip strength and cause-specific and total mortality in older disabled women. J Am Geriatr Soc. 2003;51(5):636–641. doi:10.1034/j.1600-0579.2003.00207.x
Studenski S, Perera S, Patel K, et al. Gait speed and survival in older adults. JAMA. 2011;305(1):50–58. doi:10.1001/jama.2010.1923
