The Science Behind Interval Training

After 20 minutes or so of running, I tend to get into a rhythm where each step blends into the others. If you run a lot, you’re probably used to this. There’s a particular point in a run, probably different for everyone, where you hit your stride and stop thinking so hard about what you’re doing.

This is part of why I love long-distance running. But lately I’ve been looking for ways to shake up my workout. Long-distance running only focuses on some aspects of your fitness, and I felt other areas like strength were being neglected. I wanted a way to keep running, but improve my strength and agility as well as my endurance.

If you’ve ever felt like you could use a more well-rounded workout, you might want to try a somewhat magical approach to exercise called interval training.

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What is interval training?

Interval training generally means alternating between medium- or high-intensity effort (think sprinting or running fast) and low-intensity effort (think walking or a slow jog). Unlike my standard running workout, which consists of a slow-to-moderate pace jog for 30-45 minutes without much change, interval training involves switching back and forth constantly between high- and low-intensity.

Interval training is often called High-Intensity Interval Training, or HIIT. With HIIT medium-intensity isn’t an option. When you’re not walking or slow jogging, you’re sprinting flat-out.

How it affects the body and why it’s more efficient

The main reason HIIT is so great is that you can get the same effects as a 45-minute steady cardio workout in less than half the time. HIIT pushes your body hard in short bursts, which studies have shown is useful for fitness and, perhaps counterintuitively, €”for building endurance.

One study in The Journal of Physiology found that for a group of young, sedentary men, the effects of interval training for short periods of time matched the effects of long periods of endurance training. The men were split into two groups and worked out over a six week period. One group did 40-60 minutes of cycling five times per week, a total minimum weekly workout of 200 minutes. The other group did three workouts per week of 4-6 sessions of sprint cycling for 30 seconds with 4.5 minutes of low-intensity cycling in-between. Their total minimum weekly workout time was 60 minutes.

When the study finished, both groups of men had reduced aortic stiffness, which would improve blood flow through the arteries, and better insulin sensitivity, which meant their bodies could more efficiently process glucose. Both of these outcomes could help decrease the risks of heart disease, hypertension, and diabetes, so the good news is HIIT can help improve your overall health as well as your fitness.

As the authors of a review in The Journal of Physiology point out, the fact that HIIT can be as effective as longer periods of continuous exercise “despite a substantially lower time commitment and reduced total exercise volume” is important, since “‘lack of time’ remains the most commonly cited barrier to regular exercise participation”.

Another study from the Sports Centre at the University of Birmingham has found that previously sedentary participants find HIIT more enjoyable than endurance training. Engaging in HIIT had a more positive effect on the participants’ mood and feeling of well-being than endurance training.

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Ways to get started on your HIIT workout

By now you’re probably keen to give interval training a go and see the results for yourself. Getting started is pretty easy. There are a few specific approaches to HIIT that you can implement yourself, and plenty of mobile apps to help you stay on track while you’re exercising. I’ll also throw in a couple of example workouts to help you try this approach immediately.

Tabata workout

Tabata is a system designed by Japanese professor Dr Izumi Tabata, who continues to study its effects today. The Tabata method works like this:

  • 20 seconds of high-intensity
  • 10 seconds of rest
  • repeat 6-8 times

This method takes 3-4 minutes to complete a full workout, but the intensity is high. With only 10 seconds to rest before going all out again, you’re going to get tired quickly.

Dr Tabata didn’t actually come up with this method, but helped perfect it when working with the Japanese speed skating team. The team’s head coach at the time had designed what became known as the Tabata method, and asked Dr Tabata to study the effectiveness of his training approach. Dr Tabata says “Coach Irisawa pioneered the idea, [but] somehow it became named after me”.

Although Dr Tabata continues to study the effectiveness of his method, he has found evidence already that this approach can improve the aerobic metabolism of athletes. Because the intervals are so short, your body is forced back into another high-intensity interval before it’s had time to recover from the previous one. This means, as hard as it is, €”you need to respect the timing of the intervals for Tabata to work.

Dr Tabata initially thought his method was only suitable for speed skaters, or “other highly motivated athletes”, because it’s “very painful and tiring”. He later found that many people who wanted to build muscle were focusing only on short, high-intensity exercises without improving their aerobic training. With Tabata, you get the benefits of both aerobic and strength training, and it only takes a few minutes.

Here are a few apps to keep track of your Tabata workout:

Little Method workout

This method is named after researcher Jonathan P. Little. He and his colleagues published a study in 2010 that aimed to measure the effects of HIIT when applied in a “more practical model” than many other studies used. The model they used, which is now known as the Little Method, works like this:

  • 60 seconds of high-intensity exercise (working at around 100% of your capacity)
  • 75 seconds of recovery
  • repeat 8-12 times

Although this study was very small (only seven participants were involved), the researchers found that this approach to HIIT improved the capacity of the participants as measured by time trials, and the approach to training is now a commonly used method.

I didn’t find any apps specifically designed to work with the Little Method, but there are plenty of interval training timer apps you can customize to suit your needs. Here are a few to try:

7-minute workout

Now here’s an approach to HIIT that you’ve probably heard of. The famous 7-minute workout was designed to be the most effective approach to HIIT, combining cardio and strength training is short, intense intervals, ordered for the best possible outcome. It was initially published in an article of the American College of Sports Medicine’s Health & Fitness Journal.

The routine goes like this:

  • Jumping jacks
  • Wall sit
  • Push-up
  • Abdominal crunch
  • Step-up onto chair
  • Squat
  • Triceps dip on chair
  • Plank
  • High knees/running in place
  • Lunge
  • Push-up and rotation
  • Side plank

Perform each exercise for 30 seconds. Intensity should be around 80% of your capacity.

Take 10 seconds to transition between exercises.

The order of the exercises is particularly important, according to one of the article’s authors, Human Performance Institute’s director of exercise physiology, Chris Jordan. According to Jordan, the workout makes sure all muscle groups are pushed hard, while alternating between core, lower body, upper body, and total body exercises to allow each muscle group some rest time.

To keep you on track during this workout, here are some apps for timing the exercises:

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Example high intensity workouts

If you’d rather try a simple workout than any specific method, here are a couple recommended by Greatist.

Beginner Program

Start with a 4-minute warm-up.

  • 2-minute walk
  • 2-minute jog
  • 1-minute run

Repeat 3 times through, then spend 5 minutes stretching and cooling down.

Intermediate Program

Start with a 5-minute warm-up

Repeat 6 times through, then spend 5 minutes stretching and cooling down.

Strength Program

For a more strength-based workout, try this Greatist program on for size.

Spend four minutes on each exercise, alternating between 20 seconds of maximum effort and 10 seconds of rest.

  • Leg Raises
  • Lunges (alternate legs)
  • Sit-Ups

Staying safe

Before you get stuck into your own interval training program, it’s important to make sure you’re staying safe while working out. Because HIIT requires high-intensity effort, you’re at much higher risk of injury if your technique is off.

Trainer Jennifer Cassetty offers these tips to stay safe while working hard:

  • Replace your running shoes when they start to wear down. Cassetty says you should start thinking about upgrading to a new pair after around 6 months of running.
  • Watch the length of your stride. If your body bounces, your stride is probably too short. Your feet should be landing directly underneath your body if you’ve found the right length.
  • Mix up your workouts. Cassetty recommends mixing steady-state cardio workouts with interval training to keep your cardiovascular system working well.
  • Don’t forget to stretch, warm up, and cool down.

Finally, Cassetty suggests trying interval training on a bike or elliptical if you get bored of running.

Part of what makes HIIT so great is its variability. You can create a workout that suits your needs, and change it up whenever you need a new challenge.

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