The Essential Guide to High Intensity Interval Training

High Intensity Interval Training (HIIT)

“Forget about long runs, burn more fat with HIIT”

“HIIT training: less effort, more results”

“Shred fat fast with HIIT!”

It seems lately that you can’t go to a fitness website, read a magazine, or talk to a trainer without high intensity interval training coming up.  I’m sure this isn’t the first time you’ve heard of HIIT but usually when it’s brought up people just talk about the supposed benefits and fail to mention what the hell it is.  Let’s start this article with a solid definition; according to the ACSM HIIT involves repeated bouts of high intensity effort followed by varied recovery periods.

An example of a HIIT routine might be:

6 rounds of 100m sprints with 30 second rest periods.

These short high intensity rounds are often compared with steady state cardio, which is characterized by longer exercise periods with moderate intensity.  In most forums people will testify that HIIT effectively preserves muscle mass and burns fat, while steady state training burns less fat and catabolizes muscle tissue.

Let’s look at the three major effects that HIIT is supposed to have separately.

1. HIIT’s effect on Cardio-respiratory fitness

It’s become the popular opinion that HIIT is far superior to steady state cardio.  However, in two comparison studies, comparing steady-state cardio and HIIT, both were found to have similar levels of improvement in cardiovascular fitness in obese subjects.  In these comparisons steady-state cardio actually produced a greater VO2-Peak improvement.  On the contrary: in one meta-analysis HIIT was found to be superior in improving cardio-respiratory fitness, insulin sensitivity, and it’s positive effect on inflammation.

These differing results can make it difficult to draw an accurate conclusion.  In looking at the chosen subjects for the comparative studies the focus was on obese subjects.  This may suggest that in non-trained individuals there is little difference in the benefits of High Intensity Interval Training vs. Steady State training in terms of cardio-respiratory fitness.  However, in trained individuals HIIT may produce greater results than steady state training.

This suggests that for untrained individuals, aka newbies, there is little difference between interval training and steady state training.  It’s a matter of preference.   In one study psychologists found that people tend to enjoy the shorter HIIT sessions which is likely to lead to much greater adherence and generate a much stronger preference.

Essentially, untrained individuals are likely to experience similar benefits from either steady-state or interval training.  The benefits are likely due to the fact that the individual is going from sedentary to active.  Once an unspecified level of fitness is achieved it becomes more practical to utilize high intensity interval training to continue cardio-respiratory improvements.

2. HIIT and Fat Loss

Research has shown that HIIT can significantly reduce total body mass, lead to better glucose tolerance, and can help manage the effects of a high fat diet.  The wording is the tricky part here.  HIIT reduced “Total Body Mass” which can include muscle tissue, however in the next section we’ll explain why the loss of muscle tissue due to HIIT is unlikely.

HIIT has been shown to increase the exercise work capacity of trained athletes.  A greater work capacity is associated with a greater capacity for burning fat during exercise.  Additionally HIIT appears to reduce the total amount of lipogenesis within the body, effectively lowering fat storage rates and increase fat oxidation rates.

Essentially High Intensity Interval Training does lead to weight loss while also hindering fat storage, resulting in a net loss of fat.

3. “HIIT preserves Muscle mass”

It’s common to hear around any gym that too much cardio will kill your gains.  Following this line of thinking it makes sense that minimizing the amount of time you do cardio for, the less impact on your muscle mass.

While this isn’t necessarily the case, the eventual effects look something like this.

There is a growing body of evidence that intense aerobic training can actually induce muscle growth.  This suggests that intense bouts of aerobic training (70-80% of maximal HR) actually adds to skeletal muscle, not just preserves it.

In another study researchers tested the effect of extremely low loads with high volume vs. the traditional high load, low volume resistance training model.  They concluded that high volume with low external load can lead to significant gains in skeletal muscle mass.

These findings suggest that High Intensity Interval Training may be anabolic.  In the previous section we pointed out that HIIT reduced total body mass, while this could include some muscle mass it is possible that the anabolic properties of High Intensity Interval Training outweigh the muscle breakdown, resulting in a net gain of muscle tissue.

When to HIIT

For untrained individuals both steady state cardio and HIIT produce similar results in regards to improving fitness.  This is a good thing.  HIIT workouts typically involve performing near 90% of your total work capacity.  For a trained person this is manageable but for untrained people this is likely to lead to injury and injury severely dampens adherence.

HIIT is best applied to trained individuals with specific goals (i.e. 5% fat loss, improve VO2 max, increase power output, etc…).  Unfortunately it is a current trend that many trainers will use HIIT workouts, regardless of their clients ability.  It’s alluring because it takes less time, has greater supposed benefits, and feels more intense.  Trainers and coaches in general need to be much more discriminating about determining if HIIT is a good option for their client.

For instance a 53 year old cyclist that regularly engages in endurance exercise and strength training would be a much better candidate for HIIT than a 20 year old college student with no history of exercise training looking to drop some quick pounds before spring.

The principle we should be extrapolating here is that it is better to utilize low intensity exercise to establish a solid foundation for technique and capability before engaging in higher intensity bouts.  Learn to jog before you sprint.

Examples of High Intensity Interval Training

So if you’re comfortable with high intensity exercise and have the appropriate level of ability to complete it than you are welcome to use either of my 2 favorite HIIT routines.  Guaranteed to make you sweat and reap the HIIT benefits.

Stationary Bike Intervals

On a stationary bike that allows for changes in resistance pedal for 1 minute under light resistance.  After 1 minute, pedal quickly under heavier resistance (typically 3x light resistance) for 30 seconds.  Complete 4-8 rounds.

Kettlebell Swings

This is my hands down favorite! Additionally research has shown kettlebell HIIT routines to be more effective than other popular techniques.  Use it wisely. Complete 4-8 rounds.

  • 30 seconds Kettlebell Swings
  • 45 seconds rest


In Summary

High Intensity Interval Training does greatly benefit cardio-respiratory fitness, however the benefit is equivalent to the benefits seen from steady state cardio in untrained persons.  Because there is almost no discrepancy in benefit in untrained people, it is best to begin with steady-state as it requires much less skill.

In trained individuals HIIT stimulated similar levels of fat loss in less time when compared to steady state training.  Additionally, HIIT can promote muscle synthesis and increase overall muscle mass.

When designing a HIIT routine, appeal to simplicity.  Choose a single high intensity exercise, choose an “on” time, and choose an appropriate rest time.  Try to design your routines to take no more than 12 minutes.

With an informed ability to apply HIIT to your routine, you’ll soon be reaping the benefits.  Train Smarter, Train Stronger.