What is cardio fitness?

According to the American Heart Association (AHA), cardio fitness is how well your heart and lungs utilize oxygen while you’re exercising, and this includes the level of efficiency in transporting oxygen to the muscles.

The AHA adds that low cardio fitness is a strong predictor of cardiovascular disease, as well as a factor in cardiometabolic function and even mental health.

How do you measure your cardio fitness level?

Cooper Test for VO2 Max

One of the best-known ways to get a specific measurement of cardio fitness—particularly when it comes to describing a person’s health and health risk status—is by examining VO2 max in a lab, USATF-certified coach Amie Dworecki of Running with Life tells Runner’s World. For the test, you use either a treadmill or a stationary bike while wearing a mask that analyzes how much oxygen you use as exercise intensity increases.

But if you don’t have access or just want a simpler method, it’s possible to do one of two self-tests to estimate VO2 max—called the Rockport 1-mile walk test or the Cooper 12-minute test, Dworecki says.

“In the Rockport test, you would walk a mile as fast as you can without running, and in the Cooper test, you’d run 12 minutes as quickly as possible [after an appropriate warmup],” she says. “You can take your result and enter that into a formula to calculate your VO2 max measurement.”

The formula for the Cooper 12-minute test: VO2max = (35.97 x distance covered in miles) – 11.29. You can also use an online calculator.

That means if you ran two miles in 12 minutes, your estimated VO2 max number using this formula would be 50.65.

Whether that’s classified as “good” depends on your age, fitness level, and gender, Dworecki says. But there are charts online to help you compare.

30-Minute Time Trial for Lactate Threshold

Lactate threshold can also offer a way to keep track of your fitness level. The most accurate way to measure this is also in a lab setting, where they read your blood lactate levels.

But you can also try an at-home method to estimate your threshold: “As a coach, other than direct VO2 max, I have my runners run a 30-minute time trial,” Dworecki explains. “During the time trial, they run for 30 minutes at an intensity of a 7 out of 10 or what might be described as comfortably difficult.”

Your estimated lactate threshold pace is the pace you average for 30 minutes of comfortably hard running—a pace you can maintain for just a half hour.

Lactate threshold may be an even more applicable way to measure cardio fitness for distance runners, Dworecki says. “While VO2 max represents your body’s maximum capacity to use oxygen, lactate threshold indicates how efficiently you can sustain cardio exercise before fatigue sets in, thus reflecting a marker of cardiorespiratory fitness,” she explains.

To keep tabs on your cardio fitness via lactate threshold, you could run the 30-minute time trail every four to six weeks, running at the same intensity, to determine if you ran faster or you covered more distance. These are signs that your cardio fitness is improving.

Other Lab Tests

Graded exercise tests, also known as exercise tolerance tests or stress tests (done in a clinical setting) can also test your cardiorespiratory fitness, Dworecki explains.

The Bruce protocol is a common one, often used in research, like the Journal of Clinical Medicine study mentioned above that links cardio fitness to better heart health. It starts with walking and integrates speed and incline every three minutes until you reach a specific heart rate or experience adverse symptoms like fatigue.

It often includes electrodes to measure cardiovascular function, and because it doesn’t require going to all-out exhaustion, it can be safer for some, Dworecki explains.

Can wearables accurately measure cardio fitness?

Although fitness trackers can’t match the precision of a full laboratory assessment for VO2 max, they’ve come a long way within the past few years for estimating cardio fitness, says Dworecki. These devices typically use a combination of heart rate monitoring, movement patterns, and personal data (like age and gender) to estimate VO2 max.

Studies indicate that the measurements from these devices, including Garmin and Apple Watch, certainly aren’t accurate enough for sport or healthcare application. “This type of measurement might be unacceptable for high-level or elite athletes, but it can be a good tracking number for recreational exercisers,” Dworecki says.

Just keep in mind that numbers from wearables are estimates rather than exact measurements. Dworecki compares it to tracking the weather: Using a weather app won’t be as precise as meteorology instruments, but it’s usually reliable enough for day-to-day planning.

“The real value of these devices lies in their ability to track trends over time,” she explains. “They can show you whether your fitness is improving, declining, or holding steady, which most people want to know. This can be a helpful estimate for the everyday runner looking to track their fitness.”

How does cardio fitness affect performance?

Cardio fitness is a fundamental factor that influences overall physical performance, trainer Aaron Leventhal, C.S.C.S., owner of Minneapolis-based FIT Studios, tells Runner’s World. For runners and other athletes, that might translate to speed but it’s not the only variable that cardio fitness influences.

“Those with better cardio fitness tend to have higher performance in several key ways,” he says. “That includes reaction time and even decision making in the midst of exercise.” That’s because cardio fitness doesn’t involve only your muscles and heart; research indicates it also increases blood flow to the brain, providing benefits to cognitive function.

Better cardio fitness can also lead to improved endurance, which may translate to covering more distance with better stamina, Dworecki added.

“You’ll get improved circulatory system efficiency, like a well-tuned engine for your body, which gives you better distribution of blood throughout your body during exercise,” she explains. “This means you can run farther and faster, much easier than before.”

How does cardio fitness affect health?

A higher level of efficiency in the body can be a boon not just for athletic goals, but also for your overall health. In addition to gains in longevity, heart health, and cognitive function already noted, cardio fitness can pay off in everyday life as well, Dworecki says.

“Those daily activities that used to leave you winded—climbing stairs, carrying groceries, or keeping up with children—become noticeably easier,” she explains. “Your body becomes more efficient at handling physical challenges, making life’s routine tasks feel more manageable.”

The ripple effect can also be significant. For example, better cardio fitness may improve sleep quality, which can lower stress and anxiety, leading to better mental clarity and higher emotional wellbeing.

How do you improve cardio fitness?

Whether you’ve gotten VO2 max results from a lab, some indication of your cardio fitness from a workout or wearable, or you just have a basic idea that you’re not as efficient as you could be, there are ways to improve your levels. Try these as a starting point:

Lift Heavy

A 2024 meta-analysis in Sports Medicine on middle- and long-distance runners found that training emphasizing high loads—meaning heavier weights performed for a lower number of reps—improved running economy better than other strength-training styles like isometric exercises and submaximal load sessions. Running economy measures how well you use oxygen at specific speeds (often below submaximal effort).

Researchers suggested heavy weight training could help cardio fitness by improving how muscles utilize oxygen and create greater force as a result.

Do a Mix of Run Types

Running at the same pace every day can get stale, Dworecki says, not to mention stall your progress. Instead, mix base-building easy endurance runs—which should make up about 80 percent of your training—with tempo runs, high-intensity intervals, and strides to work on leg speed. Be sure to take recovery runs, workouts, or full days off so your body can recover.

This mix of high and low intensity, as well as meaningful recovery, allows your cardiovascular system to become more adaptable and resilient, according to the Journal of Strength and Conditioning Research. Moderate-intensity workouts done regularly also prep your cardiovascular system for higher-intensity work, suggests research in Frontiers in Sports and Active Living.

Find Motivation to Keep Going

The first principle for improving any type of performance is to love what you’re doing, says Leventhal, as that creates consistency—a big part of improving cardio fitness.

“If you’re getting out there just to check a box, you won’t build enough consistency to improve your VO2 max in meaningful ways,” he added. “Sign up for a race, connect with a running group, or try running in places you find beautiful. Those actually go a long way toward keeping you motivated.”

Stay Consistent

“The secret sauce is consistency and progression,” Dworecki emphasizes. “Start where you are, gradually increase your weekly mileage, and give yourself adequate recovery between strenuous efforts. Remember that improvements in cardio fitness typically show up after four to six weeks of consistent training, so be patient and trust the process.”

A simple method for those who do not want a full-fledged run training program is to include a few high-intensity intervals into their workouts each week, she adds. A little can go a long way toward improving your cardio fitness.

“Most importantly, listen to your body,” Dworecki says. “Even elite runners take easy days and recovery weeks. During these recovery periods, your cardiovascular system adapts and strengthens, setting you up for a better performance on your next run.” And by taking those days off, you ensure you stay healthy and can keep getting out there and making gains.