The cardio guide

Steady cardio or intervals, which should you do?

By GyroscopeUpdated November 15, 202610 sources

Do most of your cardio steady and make one or two sessions a week intervals, once the steady part feels easy. Intervals give you a little more fitness for each minute, and each hard minute counts as two toward the guideline. Steady sessions are easier to recover from and easier to keep doing.

Interval training has a marketing problem. Somewhere between the fitness magazines and the boutique gyms, HIIT turned into a word for any class with loud music and a timer, and the claims grew with it: burn fat for 24 hours, get the benefits of an hour in four minutes, never jog again. Meanwhile the steady crowd swears that slow and long is the only safe way. Both camps are partly right, and the useful version is simple.

An interval session alternates hard stretches with easy ones. The easy part lets you recover enough to go hard again, so you spend more total time working hard than you could in one go. That’s the whole trick, and you can do it walking, running, cycling, rowing, swimming or on a flight of stairs.

What does an interval session look like?

Every interval session has the same parts: a warm-up, hard stretches, easy stretches between them, and a cool-down. What changes is how long and how hard each part is. Here are four, drawn on the same clock.

How much better are intervals?

A little. In 2015, three researchers pooled every controlled trial they could find that tested steady training, interval training or both in healthy adults 18 to 45 for at least two weeks. They found 28 trials with 723 people. Against people who didn’t train, steady training raised VO2 max by about 4.9 ml/kg/min and intervals by about 5.5. Head to head, intervals came out ahead by about 1.2, which the authors called “possibly small”. Both counted as large gains.

The time saving is the bigger deal for most people. In a 2016 trial, sedentary men cycled three times a week for 12 weeks. One group did 45 minutes of steady riding a session. The other did 3 all-out sprints of 20 seconds with two easy minutes between, a 10-minute session including the warm-up and cool-down. Fitness rose 19% in both groups. It was a small trial, about ten men a group, and all-out sprints are hard enough that many people won’t enjoy them.

What’s the difference between HIIT and HIT?

The old Gyroscope Cardio Guide split hard intervals in two, and the split still helps you read a class schedule.

HIIT, high-intensity interval training, means short, near all-out efforts with long rests, usually 15 to 30 seconds of work. The rest is longer than the work, so you can go flat out every time. Common shapes, as work to rest in seconds:

• 30 seconds hard, 60 easy (1:2)
• 30 seconds hard, 90 easy (1:3)
• 20 seconds hard, 40 easy (1:2)
• 20 seconds hard, 120 easy (1:6)

HIT, high-intensity training, flips it: longer work and shorter rest, so you can’t go all-out and you sit just below your limit instead. Most boot camp and circuit classes work this way:

• 45 seconds hard, 15 easy (3:1)
• 40 seconds hard, 20 easy (2:1)
• 60 seconds hard, 30 easy (2:1)

Neither is better. HIIT trains your top speed and needs long rests to do it. HIT keeps you near your limit for longer and feels like a grind. Both count as hard minutes.

What is Tabata, really?

In 1996, Izumi Tabata and his colleagues had 7 people ride an exercise bike five days a week for 6 weeks, 7 or 8 rounds of 20 seconds at about 170% of their VO2 max with 10 seconds of rest. That’s far past all-out for most people, and the session was over in about four minutes. Their VO2 max rose by 7 ml/kg/min and their anaerobic capacity by 28%. A second group that rode an hour a day at a moderate pace raised VO2 max from about 53 to 58, with no change in anaerobic capacity.

A “Tabata class” at the gym borrows the 20 and 10 timing, usually with burpees or jumps. That’s still a hard workout, but it isn’t what the study tested: 7 people, on a bike, at an intensity few people will reach with squat jumps. The old guide’s advice holds. Use it sparingly, ideally on a bike, if you’re already fit and short on time.

What about EMOMs, ladders and fartlek?

These are three more shapes from the old guide, and all of them are ways to keep a session interesting.

• EMOM, every minute on the minute. Start a set of an exercise at the top of each minute and rest for whatever’s left. Faster reps mean more rest. It’s usually a circuit, like kettlebell swings, squats and rowing.
• Ladders. Start easy and raise the speed or the incline every minute until you can’t hold good form, then drop back to the start and recover. On a treadmill, that might be a fast walk with the incline going up one notch a minute.
• Fartlek. Speed up and slow down by feel, with no clock. Run hard to the next lamppost, jog to the corner, sprint the last stretch of a hill. It works on a bike or in a pool too.

None of these has a trial behind its exact shape. They’re coaching formats, and they work for the same reason any interval does.

Are intervals for beginners?

Yes, in the gentle form. The old guide saved true HIIT for “intermediate to advanced” trainees, and all-out sprints are still a lot for someone starting from zero. But hard bursts in daily life helped people who never exercised: in 25,241 UK adults who didn’t work out, about 4.4 minutes a day of short hard bursts, like a fast flight of stairs, went with 26% to 30% lower risk of death (exercise snacks).

The interval walk is the best first step. In a trial of 246 adults around 63, people walked 3 minutes fast, fast enough to talk only in short bursts, and 3 minutes easy, five times through, four or more days a week. After 5 months their thigh strength was up 13% and their walking fitness 9%. Today’s session plays it with a beat that speeds up and slows down.

A picture from daily life

Think of carrying groceries up to an apartment. You could carry one bag at a time, slowly, all afternoon. Or you could carry four bags up one flight, set them down, catch your breath, and go again. The second way is harder, quicker and makes you stronger. But if you tried to do it every day, you’d dread grocery day. Most weeks, carry them at a steady pace and save the four-bag sprint for the days you’re short on time.

How often should you do them?

The trials that raised fitness used two or three hard sessions a week, with easier days between. The 4x4 trial used three a week for 8 weeks: 4 minutes at 90 to 95% of max heart rate and 3 minutes easy, 4 times, and it raised VO2 max more than the same work done steady (how to do the 4x4).

Hard minutes seem to help most when the rest of the week is light. In 116,221 US health professionals followed for 30 years, adding hard minutes went with lower risk in people doing under 300 brisk minutes a week, and added nothing the researchers could measure above that. A 2025 review came to a similar view: harder efforts matter most when you don’t have much time to train.

Aren’t intervals always better?

What we still don’t know

The fitness trials were short, mostly in young adults, and often small. The long studies of death followed people who chose their own mix. Nobody has assigned people to intervals or steady training for decades and counted the results, so whether one lowers the risk of dying more than the other at the same weekly total is still open. Interval sessions also haven’t been tested much in people with heart conditions outside supervised programs, so check who should talk to a doctor first before going all-out.