What The Heck Is HIIT, And Is It Bad For Me? Part 1

Jan 15, 2019

Do you feel energetic most days, or lethargic and lazy? Is there a bounce in your step? Do you want to feel vibrant and confident, ready to take on the world?

I consider myself extremely fortunate to have learned the value of movement / physical activity. From as far back as I can remember, I have been an active person. Fortunately for me, this became a life style as I grew up and entered adult life. Most of us get bogged down in 'responsible adult tasks', and forget how to be jovial, care free, and energetic.

Sadly, for most of us, our day to day lives ‘don’t make it easy’ to be physically active. Most jobs require countless hours sitting behind a desk. Leisure time typically consists of watching television and/or eating out. Unnatural and nutritionally lacking foods are often the least expensive and most accessible options available. I’m sure you’re seeing the trend. As our ‘lives get better’ through technology and convenience, our health is deteriorating at an exponential rate!

The vast majority of people do not get adequate exercise; especially in developed nations. Research shows that obesity rates in Canada have doubled over the last 40 years. In 2014, it was calculated to be 24% of the adult population (ref #1). In 2015/16, the obesity rate in the United States was determined to be 39.8% of all adults according to the Centres for Disease Control and Prevention (ref #2). My point here is that exercise (and movement generally speaking) are missing in our society, and something needs to be done about it.

When considering cardiovascular exercise, for several reasons, short intense interval training (often called HIIT) may be the preferred choice over long slower endurance training (steady state training) given (1) shorter time to complete which aligns with modern, hectic schedules, (2) it provides similar physiological benefits as longer endurance training, (3) it is trendy and many gyms offer a variety of training options. But, HIIT isn’t always better. Read on to learn why.

Current Exercise Recommendations:
In the United States, as of 2008, the United States Department of Health and Human Services “recommend the accumulation of 150 minutes of moderate or 75 minutes of vigorous activity per week” (ref #2)

What is HIIT? 
HIIT stands for “High Intensity Interval Training”. Interval training refers to exercise that alternates periods of intense work with rest, in a repeated manner. For example, running for 30 seconds, followed by walking for 30 seconds repeatedly is an example of interval training.

HIIT can be separated in to two major categories: (1) Aerobic HIIT training, and (2) “Body Weight”, or “Resistance HIIT” training (ref #3).

Aerobic HIIT training refers to any training completed (as described above with alternating work and rest) on a bicycle, rowing machine, treadmill etc. Body weight HITT refers to exercise completed involving plyometrics, calisthenics, boot camps and other classes. The end goal of alternating high intensity work periods with rest is the same. The type of equipment used differs (i.e. exercise modality differs).

Generally speaking, true HIIT training involves 20 sec of maximum effort work, with up to 40-60 sec recovery before repeating for approximately 6-12 sets.

Physiological and psychological benefits of HIIT:

  • Aerobic Fitness: The generally accepted measure of aerobic capacity is called V02 max. HIIT increases V02 max as much as, and in some studies, potentially more than steady state endurance training (ref #3)
  • Metabolic Health: “Research indicates that HIIT can increase insulin sensitivity and improve glycemic regulation, particularly in those with or at risk for type 2 Diabetes Mellitus.”
  • Vascular Health: HIIT has been shown to improve blood vessel health more so than continuous exercise.
  • Accomplishment & Mental Toughness: True HIIT workouts are very physically and mentally strenuous. Completing such a training session leaves the athlete with a euphoric feeling, a sense of accomplishment, and invincibility. It’s quite good for confidence and drive. The added benefit is that this confidence often spills over to other aspects of life!

Why you might not want to do HIIT! The Research:

Several studies have been conducted comparing HIIT vs. Continuous Training vs. Longer Moderate Intensity Intervals. The general consensus is that HIIT training yields similar benefits to continuous endurance training, as well as longer moderately difficult intervals. So, why has HIIT been promoted so much these days?

The most common complaint that people have these days is lack of time. HIIT is the perfect fit in this situation, because a very intense HIIT session consisting of only 4 minutes of total work (this excludes the rest periods), can yield similar benefits to 20 minutes of continuous training, or moderately hard interval training (ref #4).

The opposite side of the coin is that as work duration decreases with extremely intense HIIT sessions, rate of perceived exhaustion (RPE), or the level of enjoyment of the training session moves inversely! I.e. as HIIT intensity increases, workout duration decreases (which people want), but the discomfort associated with a short, super intense workout becomes extremely high. This in turn causes people to quit!

The graph below shows the general inverse relationship between intensity and time. As you can see, intensity is highest at the lowest time. As time increases, intensity decreases. It is impossible to maintain close to 100% of maximum effort for longer than 15-20 seconds. The most well conditioned athletes can maintain 90-95% max HR for prolonged periods of time, but again, that takes years of conditioning.

You now have the details on HIIT training. Check out Part 2 here, to determine whether it is right for you!

Ref #1: https://globalnews.ca/news/4456664/obesity-in-canada/
Ref #2: https://www.cdc.gov/obesity/data/adult.html
Ref #3: https://journals.lww.com/acsm-healthfitness/fulltext/2014/09000/HIGH_INTENSITY_INTERVAL_TRAINING__A_Review_of.5.aspx
Ref #4: The Effects of High Intensity Interval Training vs Steady State Training on Aerobic and Anaerobic Capacity. J Sports Sci Med. 2015 Dec; 14(4): 747–755. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4657417/ 
Ref #5: Specific muscle adaptations in type II fibers after high‐intensity interval training of well‐trained runners. T. A. Kohn, B. Essén‐Gustavsson, K. H. Myburgh. First published: 29 November 2011. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1600-0838.2010.01136.x