Cardiovascular fitness, by the numbers

Cardiovascular fitness describes how well your heart, circulation and working muscles support sustained movement. You feel it when a familiar hill becomes easier, or when you recover sooner after a brisk walk. Researchers often express it as VO₂ max, the highest rate of oxygen use during hard exercise, or in METs, a unit of exercise capacity.

Here are three numbers worth understanding before you compare scores or start a training plan.

• 1 METConventionally equals 3.5 mL of oxygen per kilogram of body weight per minute.¹
• 122,007Patients in a study linking treadmill fitness with later survival.²
• 150–300Weekly minutes of moderate aerobic activity recommended for adults by WHO.⁴

What does a fitness number measure?

Link to this section: What does a fitness number measure?

A laboratory VO₂ max test measures oxygen uptake while exercise becomes progressively harder. A treadmill test can estimate peak exercise capacity in METs from the workload reached. A one-mile walk uses your time, finishing heart rate, age, body weight and sex in an equation to estimate VO₂ max. These methods answer related questions, but their numbers are not interchangeable.

The original one-mile walk equation was developed from 343 healthy adults aged 30–69 whose oxygen uptake was also tested in a laboratory.⁵ It is useful as a field estimate when its protocol is followed; it is less certain for people outside the original study population or when the course, pace or heart-rate reading is inaccurate.

What do the long-term studies show?

Link to this section: What do the long-term studies show?

A 2009 analysis combined 33 studies. In the studies of death from any cause, the analysis included 102,980 participants. For each 1-MET higher level of estimated maximal aerobic capacity, the pooled relative risk of death during follow-up was 13% lower (risk ratio 0.87).¹ This compares groups of people. It does not mean that adding 1 MET to your own result will reduce your personal risk by exactly 13%.

Another study followed 122,007 adults referred for exercise treadmill tests for a median of 8.4 years. People in the below-average fitness group had a higher adjusted mortality rate than those in the above-average group (hazard ratio 1.41).² Because these were patients referred for testing, their results should not be treated as a personal forecast for every visitor to this site. Both studies are observational: fitness may reflect many other health and life circumstances.

Can regular walking improve fitness?

Link to this section: Can regular walking improve fitness?

In a randomized trial of 119 healthy middle-aged adults, a walking program prescribed 50 minutes, four times a week, for 15 weeks. Compared with controls, the walking group improved measured VO₂ max by an average net difference of 0.14 L/min (95% confidence interval 0.04–0.23 L/min).³ That is a group average from one study, not a guaranteed change for any individual. It does show that regular walking can improve measured aerobic capacity without requiring running.

The World Health Organization recommends 150–300 minutes of moderate aerobic activity per week, or 75–150 minutes of vigorous activity, or a combination.⁴ These are activity guidelines for health, not a requirement to reach a particular VO₂ max. If you are starting from little activity, begin with a manageable amount and build gradually.

A sensible way to use your own result

Link to this section: A sensible way to use your own result

1. Choose one method. A laboratory test, supervised treadmill test and field walk each have different levels of precision. Use the same method when checking a trend.
2. Keep conditions similar. For a one-mile walk, use the same measured route and record your time and finishing heart rate as directed.
3. Look for a pattern. A single result can shift with sleep, weather, illness, medication or measurement error. Repeated results and everyday function tell a fuller story.

If you have symptoms with exertion, significant heart or lung disease, or uncertainty about whether a brisk test is appropriate, discuss the test and activity plan with your clinician first. Stop an activity that causes concerning symptoms.

This article provides general education. It does not assess an individual's cardiovascular risk or replace medical care.