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HIIT - High Intensity Interval Training

A complete beginner’s guide to high intensity interval training

High-intensity interval training (HIIT) also known as high-intensity intermittent exercise (HIIE) is a form of exercise that you alternate between a quick bout of intense anaerobic exercise and a less intense aerobic exercise (see aerobic exercise definition). 

As its name implies, it is in fact a combination of high-intensity training and interval training, two methods known for effective fat loss. 

You can also think of HIIT workout as a two-step process as one (high-intensity training) focuses extensively on effectiveness and maximum outcomes and second (interval training) focuses on time efficiency. 

Together, it brings out the best fat-loss and calorie burning results in less time than the drive to your gym (NASM reported up to 67% less time commitment than a typical workout) . 

But that's not all. Because it's an aerobic with anaerobic characteristics, it also improves your fitness level as well as your cardiovascular health.  

A recent study found that repeatedly pushing the body close to its exercise max or limits (exercise at 85 to 95 of HRmax and / or VO2max lasting  1 to 4 minute) interspersed with intervals of rest for very brief periods is more effective than continuous moderate activity at improving cardiovascular health, respiratory, metabolic functions. 

Not too long ago, this training method was exclusively reserved for athletes seeking a competitive advantage and fitness elites wanting more results for a shorter workout period. Thankfully, the time of closed door HIIT workouts is over. 

It's now recognized as a leading training method to burn and lose fat for all fitness levels including exercise beginners. 

In fact, Huffington Post and other fitness organizations predicted HIIT training as one of the top trends for 2015.

For those looking to lose weight and drop body fat percentage, high-intensity interval training is a smart choice. 

It is shown to speed up your slim-down process as it maximizes your fat loss without losing muscle mass.
Better yet, it enhances it. 

This benefit is in fact a significant one as many aerobic exercises tend to solely do well on calorie burning, but poorly on muscle mass preservation. 

Precision Nutrition has published a study that recorded this downside of typical cardio workouts for weight loss

With HIIT, in addition to achieving major calorie burn and fat loss, you can condition your body in way that encourages development of lean muscle mass, which practically is the base of faster metabolism

Considering all the benefits of HIIT, it's no wonder this training method is all the rage in the recent years.

Interested in learning how it works?

What is high-intensity interval training - HIIT

How does HIIT work?

HIIT is pretty simple. 

You push yourself hard for a short period of time and follow up with a lower-intensity exercise (or recovery period) right after. You repeat this pattern for as many time as you want or until your time is up. 

Two great examples of HIIT training are 4-minute Tabata workout and "Chris Jordan"'s famous 7 minute workout

Why Does It Work?

Using quick bursts, high-intensity training pushes your body to its limits to achieve muscle fatigue and maximum oxygen uptake. 
 
It sounds complex, but it's really not. 

The basic principle is the harder you push your muscles to work, the more oxygen they require, and more calories you burn. 
 
The measure of the oxygen levels is VO2 max, which indicates the highest amount of oxygen your body consumes during exercise. 

Working close to your VO2 max triggers the afterburn effect, where the body continues to consume oxygen (and burns additional calories) for up to 48* hours after the workout is completed.  

Oxygen Intake and Calorie Burn

According to scientific studies, it takes approximately five calories to consume one liter of oxygen. 

Because you alternate between a short, intense effort with a period of moderate-to-low intensity effort in high-intensity interval training, researches across the globe are finding how you can get more with less. 

After extensive studies on the effectiveness and efficiency of HIIT compared to steady workouts, they found you can achieve comparable or more results in less time with this particular training method.  

One study from Applied Physiology, Nutrition and Metabolism found that high-intense interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle without spending hours at a gym. 

This simply means that the body converts both carbohydrate and fat into energy more efficiently to fuel the muscles. In even simpler terms, it means it's effective at burning fat. 
 
Another authority in exercise science, the American College of Sports Medicine (ACSM) states HIIT workouts provide similar fitness benefits as continuous aerobic endurance training but in shorter periods of time. 

They elaborated by commenting, "This is because high-intensity interval training tends to burn more calories than traditional long steady workouts, especially after the workout." 

If there is any hidden or secret benefit to HIIT exercises, this "after the workout" calorie burning is that. 
And truthfully, that's where a majority of the efficiency and effectiveness of HIIT comes from. 

By working your body harder with a very little rest period in between, you successfully elevate your body's metabolism for hours post-workout. 

In a professional term, this effect is known as EPOC or excess post exercise oxygen consumption. 

It means your body gets worked up hard that it takes hours and additional energy (calories!) to bring it back to pre-workout state.

Exactly how many hours your body keeps burning calories at a higher level depends on your workout intensity and duration, and various studies have come with a wide range of numbers. 

Some said 2 hours post-workout while others have found this effect can last up to 48 hours after you stop exercising.  

Regardless of how many hours it actually lasts, it seems that this post-workout calorie consumption can add anywhere from 6 to 15% more calories to the overall workout energy expenditure.

For most women, the purpose of exercise is calorie burning and weight loss / fat loss benefits, but there are more to HIIT.

ACSM have named other handful of benefits HIIT training can bring. 

According to ACSM, HIIT workouts improve:

  • Aerobic and anaerobic fitness
  • Blood Pressure
  • Cardiovascular health
  • Insulin sensitivity ( which helps the exercising muscles more readily use glucose for fuel to make more energy)
  • Cholesterol profiles
  • Abdominal fat and body weight while maintaining lean muscle mass.

How to Create Your Own HIIT Exercise Program?

High intensity interval training program

A few things to consider when developing an HIIT exercise program:

  • Exercise duration 
  • Intensity 
  • Recovery
  • High intensity to recovery (lower intensity) exercise ratio
  • Frequency

ACSM, ACE and NASM's HIIT general guidelines suggest the followings:

High-Intensity Interval Training Table

High intensity exercise duration

Ranging from 5 seconds to 2 minutes for women (for men, up to 3 minutes) 

Intensity  80% to 95% of a person’s estimated maximal heart rate. 
Recovery

40% to 50% of a person’s estimated maximal heart rate

High Intensity to Recovery Period Ratio

Anywhere from 1:1 to 1:3 

Frequency 3 to 5 times a week

More About Exercise Intensity

With high intensity interval training, during the high intensity work interval should range greater than or equal of estimated heart rate. As a good subjective indicator, the work interval should feel like you're exercising “hard” to very “hard”. 

Using the Joel Dowdell's "talk test" noted in his book Ultimate You, carrying on a conversion should feel difficulty at this intensity. 

Another way to assess the exercise intensity is to use a scale system. 

According to ACE, this intensity means on a 1-10 scale of perceived exertion, high intensity can be considered anything over an effort level of 7. 

More About Recovery or Low-Intensity Exercise

Low intensity interval training

The recovery intensity for intervals should be 40%-50% of your estimate heart rate. This will the physical activity that felt very comfortable and shouldn't make you out of breath. 

Treat it as an active rest where you are working your body but taking a rest from pushing yourself.  

More about the Ratio between High and Low Intensity Efforts 

The relationship between the work and recovery intervals is important. 

However, be warned that depending on which fitness authority's HIIT guideline you follow, you'll see a different set of numbers. 

ACSM suggests 1:1 ratio while NASM suggests 1:2 to 1:3. (High: Recovery) 

All while Tabata protocols and Chris Jordan's 7-minute workout are based on the upside down ratio where high intensity workout period is almost two to three times longer than the recovery period. 

To further explore the ratio and how it works, let's take the ACSM's 1:1 ratio. 

Example:

  • Ratio of 1:1 might be a 3-minute hard work (or high intensity) followed by a 3-minute recovery ( or low intensity) bout.
  • These 1:1 interval workouts often range about 3, 4 or 5 minutes followed by an equal time in recovery. 

This combination of exercise can be repeated 3 to 5 times. 

For sprint interval training, these higher intensity work efforts are typically shorter bouts (20-30 seconds) 

By combining the above principles, exercises can maximize fat-burning and muscle-building potential through significantly shorter workout sessions. 

As time is increasingly becoming the most important commodity for most women, its time-efficiency is valuable feature of HIIT. 

More About Workout Frequency

High intensity Training frequency

ACSM suggest training 3 to 5 times a week given that each workout is less than 60 minutes. 

Science behind High-Intensity Interval Training 

HIIT reaps both the benefits of aerobic and anaerobic fitness, while regular cardiovascular exercises solely address aerobic benefits.  

Aerobic exercises require the presence of oxygen to generate energy in the form of ATP or Adenosine triphosphate, while anaerobic exercises do not. 

High intensity interval training affects muscle tissue at the cellar level, actually changing mitochondrial activity in the muscles themselves.

Examples of High intensity Interval Training Protocols

Different Interval training protocols differ widely in terms of length for high and low-intensity intervals, the ratio of high to low-intensity, and the level of intensity during workouts. 

Amongst hundreds of HIIT protocols available, there are 3 that are particularly well-known and widely used. 

Three High-Intensity Interval Training Protocols:

  • Tabata Training Method
  • Little Method 
  • Turbulence Training

Tabata Training Protocol

Tabata training protocol was developed in 1996 in Japan by Dr. Izumi Tabata and his colleagues. 

Its method is based on 2:1 ratio and involves high-intensity bouts at 170% of one’s VO2 max and lasts 4 minutes including all the rest periods. 

With Tabata, you perform a total of 8 sets of 20 seconds of high intensity exercise and 10 seconds of rest

Tabata training recommends workout frequency of 2 to 4 times per week.

This HIIT protocol is best suited for those who are already fit and are looking for a workout that requires very little time. 

Although the original Tabata method used sprinting, it can also be performed with strength training exercises. 

To implement the Tabata workout, try the following workout routine:

  • 3 Minute Warming up
  • 20 Seconds Sprint
  • 10 Seconds of Rest (walk)
  • Repeat the sprint / walk cycle for a total of eight times. 

Little Method

The Little Method was developed Dr. Johnathan Little and Martin Gibala in 2009. 

This training method involves high-intensity workouts at 95% of one’s VO2 max.

The protocol calls for 60 seconds of high intensity work followed by 75 seconds of low intensity work for a total of 8-12 cycles. 

According to Gatorade Sports Science Institute's study on high-intensity-interval training published by Western Oregon University, subjects who trained 3 times per week using this method obtained gains similar to what would be expected from subjects who did steady state ( 50-70% VO2max) training five days per week.

Example of how to implement the Little Method:

  • Warm-up 3 minutes
  • Cycle for 60 seconds quickly with max resistance (at 95% of VO2 max)
  • Follow by 75 seconds of slow cycling at low resistance
  • repeat for 8-12 cycles

Repeat the fast/ slow cycle for a total of 27 minutes. 

The Little Method is best suited for those with "intermediate fitness level" and have at least 30 minutes to spare three days a week.

The Turbulence Training

The Turbulence Training was developed by an exercise physiology researcher Craig Ballantyne. This training involves eight reps of "weight training" sets alternated with one to two-minute of cardio sets.

The protocol alternates high-weight/ low-rep strength training with high intensity cardio. 

Suggested frequency of this strength training combined with cardio workout is three times per week. 

How to implement Turbulence Training

  • 5 minute warm-up
  • 8 rep set of a weightlifting movement ( like "dumbbell squat").
  • 1 minute of "burpees" or "mountain climbers"

Repeat a full-body routine for 45 minutes at max.

Turbulence Training is best suited for people who have longer time to train and want to incorporate strength training into their hiit workout routine. 

Is HIIT for You?

Despite its effectiveness, high-intensity interval training isn’t for everyone.
 
Undoubtly, it is an incredibly effective workout method that can be applied with cardio and resistance training, be warned that it's extremely intense and demanding on your body. 

If your experience with intense HIIT workouts is limited, it’s best to start gradually and slowly incorporate it into your training over time.

Even for those with sufficient fitness level and HIIT experience, gradual advancements are always recommended for safety and injury prevention. 

HIIT Workouts for Women 

For those interested in starting HIIT training, we created a strategic 4-week HIIT workout plan for women to follow and use as a guide. 

Week1: 20-Min High Intensity Interval Training Workouts to Lose Weight
Week2:
Week3:
Week4:

*The number of hours depends on the "workout intensity" and duration.

There you have it! You just learned about what high-intensity interval training is and how there are different ways to implement HIIT workouts.

We'd love to hear your experience with high intensity training! Leave us a comment below to let us know. 




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