This is The Ideal Longevity Workout

For maximum healthspan, you need both HIIT and steady-state cardio. Here’s exactly how much you need to extend your healthspan.

When it comes to cardio, there are Zone 2 zealots, and others who hammer session after session of HIIT. Who’s right?

If your goal is an increased healthspan, a new research review says you shouldn’t take sides: You need both.

Scientists looked at 18 different studies on older adults that examined the longevity-boosting effects of continuous aerobic activity (regular old cardio) and high-intensity interval training (HIIT), where bouts of intense work are alternated with periods of lighter exercise or complete rest. 

The results: HIIT aficionados increased their VO2 max, a measure of how much oxygen muscles can use, and a key indicator of healthy longevity, by 15-20 percent within six months. High-intensity work boosted study participants’ muscle strength by 12 percent and reduced fall risk. HIIT also bumped up brain power, increasing cognitive function by 10-15 percent, especially giving a jolt to memory.

Cardio work also juiced VO2 max (by 10-15 percent), and had particular benefits for mental health: Cardio exercisers had a 5-10 percent reduction in depressive symptoms, and had better mental well-being.

To get down to the nitty-gritty on using the research’s findings in your own training—how each type of cardio works, how much you should do of each, and how intense those sessions should be—I spoke with a known preacher of the aerobic gospel, Mike Nelson, Ph.D., C.S.C.S., an associate professor at the Carrick Institute.

First, Let’s Talk (Regular) Cardio

For years, “cardio” was the whipping boy of the fitness world. Why do boring, steady-state aerobic work when you could get all kinds of sexy benefits by upping your intensity? You could “torch fat” and “burn more calories for days after your workout” by trading in medium-intensity work for all-out intervals. Cardio’s benefits? They stopped as soon as you got off the “dreadmill.”

The problem, Nelson says, wasn’t with aerobic work. It was how we did it.

“What people ended up doing was saying, ‘I’m going to go for a run,’” he says. They ran as hard as they could for as long as they could with joint-busting form. As a result, they weren’t actually doing aerobic exercise, where the body can get oxygen to their muscles, and they often got injured. They didn’t get better at the exercise, or reap its benefits. They just got hurt.

The “why” for doing aerobic work, Nelson says, is that it works different muscle fibers.

“If I have a muscle fiber, and I want to make it as big as possible, I don’t have to worry about oxygen diffusing into the fiber. It’s an anaerobic fiber,” he says. Our “fast-twitch” muscles, made of these anaerobic fibers, are used to do intense work, and they draw on the carbohydrate stores in our muscles for fuel. Work these muscles, and they get bigger … but you don’t get better at using oxygen.

Cardio, on the other hand, builds aerobic fibers, or “slow-twitch” muscles. These fibers allow oxygen to pass in and out, and are able to use oxygen to fuel contraction—that’s what “aerobic” means. When these fibers get more efficient, your aerobic capacity (a.k.a. your VO2 max) improves.

So, How Intense Should My Cardio Be?

You might have heard about “Zone 2” cardio, an easy level of aerobic work that is easy to do almost every day with minimal recovery, and that builds aerobic capacity. When pro runners and elite athletes talk about “easy runs,” it’s shorthand for Zone 2. To know if you’re in this zone, you should be to do the cardio work while rattling off a long sentence—15 or so words—without needing to stop to take a breath.

This pace can be tough to find, though, and can feel uncomfortably slow, especially if you’re from the “just go for a run” school. For Nelson, finding an “easy” aerobic intensity can be even simpler than using a talk test. His goal, he says, is to go slow and be smooth.

“I think people get too stuck in, ‘oh, I need to be in this or that heart rate zone,’” he says. “Run one or two miles. Try to make it as quiet as possible … my whole goal is to be able to breathe through my nose, and see how fluid and simple and easy I can make it.”

Over the course of a few weeks, Nelson says, short workouts focused on ease and smoothness will let you do longer cardio sessions while feeling comfortable at this “easy” pace.

Cheat Sheet: How much cardio should I do?

• Aim for at least 20-30 minutes of this “easy” work six times per week. The more you do, the more your aerobic capacity will grow, Nelson says. To maintain your VO2 max and grow it slowly,

How to Use HIIT

In high-intensity interval training (HIIT), short, intense bursts of exercise are alternated with periods of easier exercise, or complete rest. This type of cardio exploded in popularity in the early aughts, and with good reason: HIIT sessions are time efficient, and burn off more body fat even when sessions are shorter than with steady-state work. There’s also all those longevity-boosting benefits explored in the 2025 review—improved cognition, memory, VO2 max, and muscle mass.

The trouble with some HIIT sessions, though, is that they aren’t HIIT at all. In order to reap all these high-intensity efforts, the intensity of the “work” sections of a HIIT workout need to be near your maximum capacity. Many exercisers just work kind of hard, doing medium-intensity intervals, Nelson says.

How Do I Do HIIT So It’s Truly High Intensity?

“The biggest bang for your buck is with intervals that target increasing your VO2 max, and we’ve got pretty good literature on that now,” Nelson says. To do this, you’ll want intervals that are longer than you might be used to, and performed at or near your VO2 max. Here’s Nelson’s tips for designing a HIIT interval session that accomplishes both:

1. Choose a cardio modality where it’s easy to get to your max, and repeat it: Running and normal cycling are tough for true high-intensity interval training, because it’s hard to reach and maintain a maximum effort. Nelson recommends the rowing machine, or a stationary bike with arm action (like an Assault bike).

2. Perform intervals of 2-6 minutes: While some intervals have shown results with shorter work durations, Nelson says, most of those studies were on untrained populations. Your best bet is to go over 120 seconds per effort.

3. Work at or near your VO2 max during the work portion: This is the key to getting results, Nelson says. You want to be working as hard as you can for the length of every interval. If you’re using a rower, you can do a simple VO2 max test: Just row 2,000 meters as fast as you can in one session, then put the number into this calculator (there’s science behind this). During the work portion of your intervals, that’s how fast and hard you should row.

4. Rest completely between intervals: Stop working all together after your 2-6 minute bout, and let your heart rate come down below 100 or 90 bpm. This may take several minutes.

5. Repeat only as many times as you can maintain the same work intensity: When you start your second interval, the intensity of your work and speed needs to match the first interval. Same goes for the third, fourth, or however many you do. If you can’t maintain that level of intensity, end the workout, Nelson says: You’re not getting the benefits anymore. Come back in your next session, and see if you can complete the “failed” interval at the full intensity.

Cheat Sheet: How much HIIT should I do?

• One VO2 max interval session per week. Start trying to do just two or three intervals. It may take months, but try to build up to 5-7.