The 5 study-backed reasons you should HIIT the gym

This is your science-approved guide to high-intensity interval training.


If the New Year has you thinking about how to stay active and how to boost your health in 2020, then you might be tempted to try high-intensity interval training (HIIT). HIIT workouts are composed of grueling training regimens that proponents say help build muscle, shed pounds, and boost heart health.

But are these workouts just another fad trend that is more hype than substance? Inverse looked at the science to find out if HIIT workouts actually work — and if it does, whether it is right for you.

What are HIIT workouts?

High-intensity interval training doesn’t follow a specific regimen or focus on any one type of exercise. Instead, it involves short, intense bursts of activity, interspaced with with rest periods. These bursts can be short — just 30 seconds can make all the difference — or more substantial, up to 4 minutes. Some say you should aim to do these intervals over the course of 30 minutes, but some might last longer.

The most popular HIIT workouts include cycling, running, kettlebell lifting, rowing, and climbing stairs. Workouts might also include burpees, box jumps, squat jumps — all that cool stuff you see fit folks powering through with barely a shine on their foreheads on Instagram. Really, it is up to you. The main thing though is that you go flat out for a short time, and then rest, rinse, and repeat.

Does HIIT give fast results?

Fans of HIIT say that it allows them to get health benefits similar to moderate intensity activity — like long-distance running — in a shorter amount of time. It might even give you the same benefits in half the time, according to a study published in 2008 in the American Journal of Physiology.

HIIT can elevate your metabolic rate after the workout is finished.

Unsplash / Meghan Holmes

Researchers studied 20 people as they did sprint-interval training for six weeks, while another group did moderate cycling for the same time period. Stacked against one another, the interval trainers had more improvements to their metabolism — a signal that they were getting fitter faster than the cyclists. Interval training, the researchers conclude, may be a “time-efficient strategy” to get similar heart health benefits to long-term endurance training.

Does HIIT burn more fat than regular exercise?

A 2011 study, published in the Journal of Obesity, suggests that HIIT burns more fat than does traditional cardio — and the benefits last for hours after the workout is done. The researchers aren’t sure exactly why this is the case, but it could be that HIIT triggers the body to burn more fat both during and immediately after the workout. It could also be because HIIT suppresses your appetite — leading you to eat less through the day, they say.

More recent research backs up these results. A separate study published in 2018 in the British Journal of Sports Research compared HIIT against moderate intensity, steady-state workouts. HIIT led to nearly 30 percent greater reductions in total absolute fat mass, compared with steady-state exercise, according to the results. Taken together, the evidence suggests that yes, HIIT really could help you burn more fat faster than regular exercise.

What does HIIT do to your heart?

Losing weight isn’t the only reason to work out. Keeping your heart healthy — so it can, you know, keep you alive — is one of the top benefits of any cardio regimen.

HIIT pushes exercisers to their aerobic limits, and over time, can raise the threshold for the amount of work people are able to do.

A 2014 analysis in the British Journal of Sports Medicine demonstrates that, in people with chronic lifestyle-induced diseases — like type II diabetes and atherosclerotic cardiovascular disease — HIIT significantly improved the heart’s ability to pump oxygen round the body compared to mid-range intensity workouts.

Another study published in the journal Circulation came to similar conclusions. Exercise intensity, the researchers found, can improve aerobic capacity and quality of life — among other benefits — in people who have had heart failure.

To get a read on how HIIT affects your heart, you might consider wearing a heart monitor. If you are at-risk for cardiac problems, talk to your doctor before you start the program.

What does HIIT do to your body?

Exercise can help your body do better at its many jobs — like using oxygen more efficiently. But HIIT seems particularly adept at improving oxygen flow, according to a wealth of studies.

A 2015 analysis found that HIIT is more effective than endurance training when it came to gains in VO2 max, a metric of how well your body consumes oxygen.

That’s important because your body needs to supply oxygen to your muscles when you work out. If that doesn’t happen properly, your muscles may cramp, with the potential for injury.

The reason why is to do with how HIIT works. The regimen pushes you to the limit just before it’s time to back off with a low-intensity rest. Doing that repeatedly means that, over time, your limit begins to stretch as your body becomes habituated to making good use of oxygen.

How to make HIIT a habit

Establishing a specific time to work out, and fitting it directly into your routine, may be the most effective way to keep you at HIIT for the long-term. You can start by working out at the same time every day. For example, your morning might look like this: Wake up, brush teeth, work out, eat breakfast, cold shower, go to work.

As Inverse previously reported, working out at the same time every day builds “automaticity,” scientists say.

Doing so makes your routine so reliable as to take all the mental tax out of it. So instead trying to make yourself get to the gym, you just do it — because it’s the step that comes after “brush teeth.”

Should you do HIIT if you are obese?

Despite the fat-burning effect associated with HIIT, some research suggests people who are obese may not benefit as much as you would think. A 2010 study compared HIIT with traditional exercise methods as a means of promoting health in obese people. While HIIT did lead to bigger improvements in some areas — namely, oxygen pumping and glucose tolerance — it wasn’t as effective as the traditional exercise regimens in others, like improvements in muscle mass or skeletal health.

So, is HIIT right for you? If you’re looking to improve heart health and simply get fit — and who amongst us isn’t? — it might be worth a shot. But talk to your doctor before starting any new workout regimen.

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