Which Exercise Metrics Actually Matter for Longevity?

In the earlier parts of this Hype vs Reality: Exercise & Longevity series, we looked at the fundamentals: how different types of training actually affect healthspan and lifespan. This final chapter looks into how to analyze the measurable changes using exercise and recovery metrics. We’ve broken down for you VO₂ max, RHR, HRV, HRR, respiratory rate, blood oxygen levels, & “readiness” and “wellness” scores. Many voices insist one or a combination of these being the true longevity metric, and that their dashboard is the one you should live and die by.

This article is about pulling that back to something grounded in reality, separating yourself from the hype: What do these metrics actually measure, how are they defined, what do they really tell us about longevity, and how should a person use them without getting lost in the noise. For readers short on time, the key takeaways and practical guidelines are summarized at the end of the article before references.

For this article, a longevity exercise metric is:

Some of these metrics have decades of data behind them. Others, especially composite “scores”, are much newer and mostly driven by wearables like your Apple Watch, Whoop, or Oura Ring.

VO₂ max is the maximum amount of oxygen your body can use during intense exercise. Think of it as “how powerful your heart-and-lung engine is when you floor the gas pedal.” The reason everyone should pay attention to this metric is that large human studies show cardiorespiratory fitness is one of the strongest single predictors of both overall survival and future risk of cardiovascular disease.

It began as a laboratory measurement: during a graded treadmill or cycle test, a mask and gas analyzer directly measure how much oxygen a person can use at maximal effort. Because this is expensive and impractical for routine use, researchers built equations to predict VO₂ max from simpler tests like speed, power, heart rate, age, and body size. Modern wearables extend this idea by using values that are easy to collect from the device itself, such as heart rate and movement data. What your watch reports is therefore not VO₂ max itself, but an estimate used as a proxy for cardiorespiratory fitness. As such, it should be treated as an approximate indicator for tracking trends over time, not as an exact clinical value.

Over time, large meta-analyses showed a very consistent pattern: people with higher CRF have much lower risk of dying from any cause and from cardiovascular disease [1]. More specifically, moving from low to moderate CRF can cut mortality risk by around 30-40%, and each step up in fitness (often measured as METs, a unit of exercise capacity we covered in our previous piece) brings additional risk reductions [1,3].

One influential statement from the American Heart Association now argues that CRF is so important it should be treated as a clinical vital sign, just like blood pressure [2].

For context, many reference charts classify VO₂ max in the mid-30s to low 40s (mL/kg/min) as roughly average for adults in midlife (20-49 years old), while values in the high 40s and above are generally considered “good to excellent” for non-athletes of the same age and sex [1-3].

Your resting heart rate is how many times your heart beats per minute when you’re relaxed and at rest (often best measured during sleep).

A meta-analysis of 46 studies with over 1.2 million people found that for every 10 beats per minute increase in resting heart rate, the relative risk of all-cause mortality rose by about 9%, and cardiovascular mortality by about 8% [4]. So, a chronically higher resting heart rate is a measurable risk factor.

Resting heart rate is a kind of “idle speed” for the body, and it reflects several systems at once. A more efficient heart can pump more blood with each beat, so it does not need to beat as often, which lowers resting heart rate. A well-balanced nervous system, with stronger “rest-and-digest” activity and less constant “fight-or-flight” activation, also tends to slow the heart at rest, while ongoing stress, poor sleep, or illness can keep it higher. Over time, regular exercise usually improves heart function, blood vessel health, and this nervous system balance, so resting heart rate often falls as fitness improves and stays higher when fitness and recovery are poor.

Look at trends over weeks, not isolated numbers. If training, sleep, and stress management bring your average down over time, that’s usually a good sign. If it drifts up and stays up for no obvious reason, it’s a prompt to investigate.

For most adults, a resting heart rate somewhere around 60-80 beats per minute is common, with persistent values above ~80-90 bpm linked to higher long-term risk in large cohorts, and lower values (especially in the 50s) often seen in fitter individuals [4].

HRV measures how much the time between individual heartbeats varies. More variation (within a normal range) generally indicates a flexible, adaptable autonomic nervous system, the part of your nervous system that runs the body’s “autopilot” functions.

A large meta-analysis of 32 studies and a total of 38,008 participants found that lower HRV is associated with higher all-cause and cardiac mortality [5]. A separate meta-analysis in patients with cardiovascular disease shows the same pattern: low HRV is linked to higher risk of death and cardiac events [6].

Heart rate variability is highly individual, so what looks “low” for you might be “high” for someone else. It is very sensitive to factors like stress, alcohol, sleep, illness, hormones, and even when and how it is measured, so day-to-day changes are normal and not necessarily worrying. On top of that, different devices calculate and average HRV in different ways; some are fairly reliable, especially for nighttime readings, while others are less accurate [12].

Rather than obsessing over a single daily score:

Unlike VO₂ max or resting heart rate, there are no universally agreed “good” HRV numbers for the general population. What matters most is your own baseline and trend over time, not how your value compares to someone else’s. You can’t directly “boost” HRV on command, but you can improve the things that directly influence it, like regular aerobic exercise, good-quality sleep, and better stress management. Over time, your typical HRV pattern often becomes more stable and more favorable.

HRR is how quickly your heart rate drops in the first minute or two after exercise. It shows how fast your “rest-and-digest” system comes back online.

In a classic study of more than 2,400 adults referred for treadmill testing, people whose heart rate fell 12 beats per minute or less in the first minute after exercise had about four times the risk of death over six years, compared with those with faster recovery [7]. Another large cohort with coronary disease showed that slow HRR predicted mortality even after accounting for how severe their artery blockages were [8].

Heart rate recovery reflects both your cardiorespiratory fitness and how flexible your autonomic nervous system is during and after stress. When you stop exercising, a well-conditioned heart and a healthy “rest-and-digest” response allow your heart rate to drop more quickly because your body no longer needs to pump as hard and your nervous system can rapidly shift out of “fight-or-flight” mode. For this reason, a faster fall in heart rate after exercise is generally considered a good sign, provided the exercise itself is appropriate and safe for you.

After a steady bout of exercise (a brisk walk, run, or cycle):

Over months, if the difference grows (for similar workouts), that’s usually a sign your system is adapting well. If HRR gets clearly worse and stays worse, especially with other symptoms, that’s something to bring to a doctor.

Generally, in a healthy adult, a fall of around 18-20 beats or more in the first minute after a hard but safe effort is often considered a favorable sign [7,8].

This metric indicates your resting breathing rate, usually breaths per minute.

In hospitals, respiratory rate is one of the most sensitive early warning signs that a patient is deteriorating; it’s part of almost every early-warning scoring system [9]. A study in older outpatients found that higher resting respiratory rate was associated with increased all-cause mortality over follow-up, even when values were still in a range many would call “normal.” [9]

For a generally healthy person, respiratory rate is less about fine-tuning performance and more about spotting when something is off:

For most healthy adults, resting breathing is usually around 12-20 breaths per minute. A clear, sustained rise above this, especially if you also feel unwell or short of breath, is a reason to seek medical advice [9]. So, if your wearable often shows unusually high resting RR, especially at night, that’s a reason to check in with a clinician rather than tweak training zones.

SpO₂ is a measure of how much oxygen your blood is carrying, usually shown as a percentage and measured by a small finger clip or a sensor on a wearable device.

A Norwegian cohort study followed over 5,000 adults and found that a single low resting SpO₂ (≤95%) was associated with higher all-cause mortality and deaths from lung disease, independent of smoking and other risk factors [10].

In acute illnesses (like pneumonia or COVID-19), lower SpO₂ at presentation strongly predicts worse outcomes and higher in-hospital mortality [10,11].

So SpO₂ is best thought of as a safety metric: it tells you when you might need help, not how “optimized” your fitness is.

“Readiness,” “recovery,” or “wellness” scores (from Oura, WHOOP, Garmin, etc.) combine things like sleep duration and quality, RHR and HRV, recent activity and strain, and sometimes temperature or respiratory rate into a single 0-100-style number that claims to say how “ready” or “recovered” you are.

A 2023 study using Oura data found that day-to-day readiness scores tracked fairly well with changes in sleep duration, timing, and efficiency, as well as with next-day mood, motivation, and sleepiness. In other words, they capture how recovered you feel, at least to a rough degree [11].

But a 2025 evaluation of composite health scores from major wearables concluded that their algorithms are largely proprietary and not transparent, that they have only limited validation across different types of people, and that it is still unclear how directly useful these scores are for guiding long-term health or predicting mortality [12].

So they’re built on real physiological ingredients, but the overall score is still somewhat of a “black box.”

Treat these scores as a coach’s gentle suggestion, not a medical test:

Because each wearable uses its own proprietary formula, there is no evidence-based “good” or “bad” readiness or wellness score cut-off for long-term health. These scores are best treated as rough guidance for day-to-day training and recovery decisions, not as true longevity markers, and so far, no study has shown that keeping your readiness above any specific threshold makes you live longer.

The metrics we covered capture different aspects of how your heart, lungs, blood vessels, nervous system, and daily behaviors function today, and together they offer a practical snapshot of your long-term health trajectory. Below is a concise summary of what to pay attention to for each metric, what changes in those values usually mean in real time, and how you can use them to steer your training and lifestyle in a direction that supports healthier, longer living.

Across all of these various metrics, the core message is the same: use the data to inform your decisions, not drive anxiety. The interventions that improve most of them are still the fundamentals, including regular exercise, adequate sleep, effective stress management, and a generally healthy lifestyle, applied consistently over the long term.