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What is HIIT?  

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HIIT workouts generally combine short bursts of intense exercise with periods of rest or lower-intensity exercise. At fitness studios and online, these workouts often mix aerobic and resistance training. 

When researchers talk about HIIT, they’re referring to workouts that alternate hard-charging intervals, during which a person’s heart rate reaches at least 80% of its maximum capacity usually for 1-5 mins, with periods of rest or less intense exercise. (It’s not easy to know that you’re working at 80 per cent, but a heart rate monitor can help.) 

 

What does a HIIT routine look like? 

What differentiates HIIT from the steady-state, continuous types of exercise (e.g. jogging at an even pace or walking) is the intervals, those periods of heart-pounding intensity. If you want to try it, you can simply take a HIIT class, or run or even walk in a way that involves higher-speed and higher-incline bursts. 

If you want a routine that’s been lab-tested, there’s the 4 by 4 from Norway.

  • Jog for 10 minutes to warm up

  • Then four  x  four-minute intervals of faster running

  • Three  x three-minute intervals of moderate jogging or brisk walking in between

  • Five-minute cool down at the end.

And you can substitute jogging with other aerobic exercises, such as biking or swimming. The whole routine should take 40 minutes.

 

A shorter, and also heavily studied, example of an interval routine is the 10 by 1 which involves ten x one-minute bursts of exercise each followed by one minute of recovery. 

What are the benefits of interval training?

  1. Heart health.

  2. Respiratory health

  3. Weight loss

  4. Mental resilience

 

Intervals can boost cardio-respiratory health with a smaller time investment compared to continuous forms of exercise. So, we’re not talking about superior fat-burning capacity or bigger muscles. We’re talking about improved VO2 max, a measure of endurance that calculates the maximum volume of oxygen the body can use.

Scientists have found that [VO2 max] is one of the best predictors of overall health,” according to the recent interval training book, “The One Minute interval” co-authored by Martin Gibala (one of the world’s leading interval training experts based at McMaster University in Canada).

 

The more aerobically fit you are, the better your heart can pump blood, the longer it takes you to get out of breath, and the farther and faster you’re able to bike or run or swim.”

 

And that, in turn, can help prevent heart disease.

HIIT is a time-efficient strategy to get the benefits typically associated with longer bouts of traditional cardio. Of course, the more you put into a HIIT workout, the more heart health benefits you get out. 

Why does HIIT improve cardio health? 

Researchers still haven’t figured out exactly why HIIT works to improve aerobic fitness more than continuous types of exercise. But one key hypothesis has to do with the heart’s ability to pump blood. One measure for blood pumping is something called stroke volume, or the volume of blood that comes out when the heart contracts. And a major determinant of VO2 max is stroke volume.

The maximum amount of blood that comes out of the heart is improved by exercise training and there’s evidence that when you do interval exercise training, the stroke volume increases even more.

Is HIIT the best exercise regimen for weight loss? 

There’s no doubt that interval training can be a time-efficient way to burn calories. Researchers have repeatedly shown that people can burn comparable amounts of calories in HIIT routines lasting, say, 20 minutes, compared to longer continuous exercise routines lasting, say, 50 minutes.

 

The reason for that is that higher-intensity exercise, like intervals, results in a greater disturbance of the body’s homeostasis, and it literally takes more energy and oxygen to return it to normal basal levels.

 

It must be noted however that it’s much easier to lose weight by cutting calories in your diet than trying to burn excess calories. In terms of the overall magnitude of calorie burning, weight loss tends to be small relative to what you can achieve by dietary changes.

Intervals can be demanding mentally and physically, so some steady-state continuous is nice once in a while, but for those who truly are super time-pressed and can tolerate intervals almost exclusively, it’s the most efficient way to train.