Whatever your running goals, you should execute most of your miles at an easy effort. But when it comes to workouts designed to challenge your VO₂ max, if they don’t feel pretty dang punishing, well, you’re doing them wrong.
If you’re not familiar with VO₂ max, it stands for the maximal volume of oxygen (O₂) that your body can use to work aerobically. “As we go harder and harder, we need to produce energy faster and faster, so we need more oxygen—and you’ll see this straight-line increase in our oxygen consumption,” explains Trevor Connor, exercise physiologist, coach, and CEO of Fast Talk Labs in Boulder, Colorado. “At a certain point, it levels off and we can’t consume any more oxygen than we already are; that’s called your VO₂ max.” (To push yourself beyond that point, you have to produce energy anaerobically, which isn’t sustainable for very long.)
Your VO₂ max is only one part of your overall fitness, but training to improve it so you’re able to consume and use more oxygen can help you run faster with less effort. “It means you have a larger aerobic ceiling,” says Mike Thomson, personal trainer and run coach at Life Time Overland Park in Kansas. “You’ll have better diameter of your capillaries and greater stroke volume per heartbeat. The higher your VO₂ max, the higher your threshold and the better your potential.”
To train this, you’ll need workouts that tap into the right effort level. Here’s more about why you should be doing VO₂ max workouts (plus which runners might want to skip them), and how hard to push yourself so you reap the biggest rewards.
The Intensity to Hit for VO₂ Max Workouts—and Why They’re So Beneficial for Runners
Generally speaking, you train your VO₂ max with interval workouts, and those intervals should reach heart rate zone 5, or around 90 percent of your max.
If you prefer to gauge intensity with rate of perceived exertion (RPE), you’ll want to aim for around an 8 out of 10 to start, with 10 being all-out effort, and expect that to feel more like 9 by the end of the interval, says Connor. That means you shouldn’t be able to talk. The idea is that with these sessions, you’re increasing the amount of time you’re able to spend at your VO₂ max and increasing your oxygen consumption.
“Those intervals are great, but when you have somebody who’s fairly well trained, you’re not going to see much improvement in VO₂ max,” says Connor. That’s because the possible gains in VO₂ aren’t infinite; you can boost yours only so much. “The truth of the matter is, most people max out their VO₂ max very early on when they take up training,” he says.
However, that doesn’t mean you should sideline VO₂ max workouts. Even if you’ve tapped your full potential for this metric, these sessions can still make you a stronger runner by spurring additional physiological adaptations, says Connor. For example, workouts at this high of an intensity are one way to promote an important protein in our cells called PGC-1 alpha. “That’s responsible for a whole lot of our aerobic adaptations—like increasing our mitochondrial density, increasing our ability to use fat for fuel, and increasing our ability to take up oxygen,” he explains. All of these payoffs lead to better performance, especially for long-distance athletes.
Even better: Research shows a link between a higher VO₂ max and a longer life, as well as decreased cancer mortality risk. So you’re not only increasing your fitness level with these workouts, but also your overall health and longevity.
How to Do VO₂ Max Intervals
The repeats in a VO₂ max session can be broken up into longer intervals or shorter bursts.
Traditionally, researchers thought longer intervals (think: five minutes at 90 percent of your max with a 2.5- to 5-minute recovery between repeats) were best. “But ask anybody who has tried those intervals—they are miserable,” says Connor.
So another popular way to achieve VO₂ max benefits, especially for those new to them, is with 30/30 intervals: You run as hard as you can for 30 seconds, then jog slowly for 30 seconds. Repeat that five times (for one six-minute set), rest five to six minutes, then repeat the whole thing for three sets. An older but landmark study found that these shorter bursts allowed runners to hold an effort close to their VO₂ max for more time than when using longer intervals.
Try adding this workout to your schedule once or twice a week. Keep in mind that intervals at this high intensity are hard on your body and you don’t want to continue them every week, indefinitely. Connor recommends doing them for only five or six weeks at a time, then pulling back to easier runs for at least two weeks; the rest gives your body a break and a chance to make the VO₂ gains you’ve been working toward. After that recovery window, you can resume VO₂ max sessions or focus on other speedwork.
Because these sessions are tough and high impact on the body, runners should be cautious when jumping into them, advises Thomson. “People with heart issues or a cortisol issue should seek professional support so they don’t do too much,” he says. “And all runners need to build their capacity so their tendons and tissues can tolerate the intensity.”
That means slowly introducing interval training, like starting with just one set of those 30/30 intervals and building up to three. You could also try them on an AssaultBike or rower first to lessen the impact before doing the full running VO₂ max workout.
How to Know You’re Pushing Yourself Hard Enough
Bottom line: VO₂ max sessions should feel very difficult. It’s not really possible to go too hard unless you wind up not being able to finish it. “If you go out and can’t maintain the same effort for the duration of all the intervals, you’ve gone too hard,” says Thomson.
Finding the sweet spot for the intensity that’s tough enough but not so grueling that you can’t eke out the last few intervals takes some practice. “The first time I give these to an athlete, I warn them, ‘You are not going to execute these well the first time,’” says Connor. “That’s okay. This is just you figuring it out.”
Like so many aspects of training, it takes some trial and error to do it right—but once you do, it’s well worth your time.
Laurel Leicht is a writer and editor in Brooklyn. She’s covered health, fitness, and travel for outlets including Well+Good, Glamour, and O, The Oprah Magazine.