High Intensity Interval Training (HIIT): A More Functional Path to Fitness?
- Sep 6, 2023
- 6 min read
Typically, Low Intensity Steady State Training (LISS), or Moderate Intensity Continuous Training (MICT) aerobic endurance exercise has been promoted as the vital and optimal means of improving cardiovascular and cardiorespiratory health.
Current recommendations include exercising at 50-85% of heart rate max (calculated as 220minus your age) for extended duration. Low intensity exercise would focus on a heart rate that falls closer to 50% of HR max , and moderate intensity exercise would yield heart rates closer to 65-75% of the max recommended heart rate for your age. A more rigorous workout for a trained individual would shoot for achieving levels closer to 85% of heart rate max (High Intensity Continuous Training, HICT).
The following are the recommendations from the American Heart Association. Note that the recommended durations are 150 minutes per week for moderate activity and 75 minutes per week for intense activity. It is assumed that these are likely broken up into bout durations of 50 mins (3x per week) or 25 mins (3x per week), but the recommendation is clearly for EXTENDED duration of MAINTAINED aerobic exercise in order to maximize heart health.
Activity and Fitness Recommendations for Adults per the American Heart Association
Get at least 150 minutes per week of moderate-intensity aerobic activity or 75 minutes per week of vigorous aerobic activity, or a combination of both, preferably spread throughout the week.
Recommendation refers to Moderate Intensity Continuous Training (MICT)and High Intensity Continuous Training (HICT).
Add moderate- to high-intensity muscle-strengthening activity (such as resistance or weights) on at least 2 days per week.
Recommendation refers to Moderate Intensity Continuous Training (MICT)and High Intensity Continuous Training (HICT) of the heart (and skeletal muscles) per strength training.
Spend less time sitting. Even light-intensity activity can offset some of the risks of being sedentary.
Recommendation refers to Low Intensity Steady State Training (LISS) and acknowledges the health risks of sedentary lifestyle.
Gain even more benefits by being active at least 300 minutes (5 hours) per week.
Recommendation refers to Low Intensity Steady State Training (LISS) and acknowledges the health risks of sedentary lifestyle.
Increase amount and intensity gradually over time.
Recommendation encourages moving from low intensity steady state training-->moderate intensity continuous training-->high intensity continuous training. Recommendation encourages working toward greater frequency and duration of continuous/steady state cardio exercise .
General Recommendations for Cardio Exercise (LISS/MICT/HICT)
This morning, I was perusing the internet with my morning google search of current health topics, and I came upon an article from Very Well Fit, entitle "Everything You Need to Know about Cardio." The information in the article appeared to be pretty standard. Some of the benefits of cardio that are listed in that article, and confirmed by a great deal of research are as follows: Cardio burns fat and calories; improves sleep, lung capacity and confidence; promotes better mental health; reduces the risk of heart attack, high blood pressure, diabetes and cancer; improves cholesterol levels; and strengthens the heart.
One of the final quotes of this article is as such:
"There are very few activities you can do for a short period of time that have all of the physical and mental health benefits that cardio exercise offers." This statement is referring to LISS/MICT/HICT cardio training, and is definitely the general consensus on fitness: if you want your heart to work well and to achieve overall health , you have to increase your heart rate and maintain that elevated rate for extended periods several times per week. In other words, in order to have a healthy heart, you work hard enough to achieve 50-85% of your heart rate max, you maintain that rate for 25-50 mins, and you do this 2-3x per week. But are these ideas exclusively true, or are there other, perhaps even more functional paths to cardiac fitness??
In the following paragraphs, we will discuss research related to other means of achieving heart health. The focus will be on evaluating the benefits of High Intensity Interval Training (HIIT), although I cannot miss the opportunity to bring to your attention the significant impact that extended sitting has on heart health! Some research even indicates that you cannot make up for too much sitting by being active, no matter how you exercise your heart! (Look for additional posts about "Sitting. The New Smoking.")
Our Ancestors and High Intensity Interval Training (HIIT)
Considering how our ancestors functioned and needed to function is a reasonable consideration, as we know that their adaptations have been passed down to us genetically over the centuries. If you think of early hunter-gatherers, you can imagine that their activity consisted of short bursts of very intense activity, followed by periods of rest, and then, perhaps, a return to a burst of intense activity. This type of activity would have been necessary to escape a predator, or in order to catch a prey for food. It would have been highly unlikely that early hunter-gatherers would have needed to engage in sustained bouts (25-50 mins) of intense aerobic activity, like running, three times a week! How is it , then, that hunter-gatherers were able to maintain their fitness and function? Perhaps their lifestyles promoted a more natural and functional means of attaining fitness that looked a lot more like High Intensity Interval Training than like Low Intensity Steady State Training or Moderate to High Intensity Continuous Training?
High Intensity Interval Training (HIIT)
High intensity interval training (HIIT) is a form of exercise in which short periods of more demanding physical activity are alternated with much less intense recovery or rest periods. "Although there is no universal definition, high-intensity interval exercise is characterized by repeated short bursts of intense activity, performed with a “near maximal” or “all-out” effort corresponding to ≥90% of maximal oxygen uptake or >75% of maximal power, coupled with periods of rest or low-intensity exercise. "
(From Evidence-Based Effects of High-Intensity Interval Training on Exercise Capacity and Health: A Review with Historical Perspective. See below.)
What does the Research say about High Intensity Interval Training (HIIT)?
Not only does HIIT appear to be much more consistent with our ancestral health related to the activity of early hunter-gatherers , but a great deal of research suggests that HIIT workouts, in many ways, might be the most optimal option for maximizing physical fitness. Let's take a look at several of these research studies....
1. Evidence-Based Effects of High-Intensity Interval Training on Exercise Capacity and Health: A Review with Historical Perspective
The above cited review offers the following comparisons of HIIT versus MICT:
High Intensity Interval Training Moderate Intensity Continuous Training
Stimulates central cardiovascular adaptations (referring to adaptations of the central nervous system-HRV?) and metabolic efficiency | Primarily improves oxygenation of muscles and metabolic efficiency. (In other words, MICT does not promote significant changes in the central nervous system.) |
Lower drop out rates in sedentary individuals when resting periods are adequate | Greater drop out rates due to time requirements |
Improves V˙O2 max, endurance capacity ,resting metabolic rate , substrate metabolism, body composition , insulin sensitivity, and cognitive functions. Decreases the risk for cardiovascular diseases , breast cancer, metabolic syndrome, and, osteoarthritis. | Promotes similar adaptations to HIIT. Does not significantly impact central cardiovascular control (heart rate variability?) |
Greater exercise commitment due to lower time requirements | Lesser levels of exercise commitment due to increased time commitment necessary to promote the above changes |
Induces adaptations similar to MICT despite lower exercise volume (in less time). | Requires greater time commitment than HIIT to promote the above changes. |
Higher Enjoyment Level | Lower enjoyment level. |
2. The Effects of High-Intensity Interval Training vs. Moderate-Intensity Continuous Training on Heart Rate Variability in Physically Inactive Adults https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6069078/
High Intensity Interval Training Moderate Intensity Continuous Training
20 min of interval training with cycling to rest ratio of 10/50 s at ≥90% HR peak | 40 mins of continuous cycling at 60-75% HR peak |
Both groups completed eight sessions of training within two weeks. | Both groups completed eight sessions of training within two weeks. |
The HIIT program was superior to MICT in improving Heart rate Variability (HRV) in physically inactive adults. | |
Check out our post on Heart Rate Variability (HRV)!!
3. Impact of high intensity interval training on cardiorespiratory fitness, body composition, physical fitness, and metabolic parameters in older adults: a meta-analysis of randomized controlled trials. https://pubmed.ncbi.nlm.nih.gov/33836261/
High Intensity Interval Training
Effective for improving *VO2 Peak |
Induces favorable changes in respect to cardiorespiratory and physical fitness and strength |
*Improves mitochondrial citrate synthase activity , a marker for intact mitochondria, or the cells' energy production factory. In other words, HIIT improves energy production in the cell. |
Decreases blood triglyceride and glucose levels in older adults.--decreases the "bad fats" and stabilizes blood sugar |
High intensity interval training significantly improved the rate of the ability of the body to use oxygen when compared to MICT |
Recommended total duration: training periods of greater than 12 weeks most beneficial |
Recommended frequencies of two sessions per week |
Recommended total duration of each session: lengths of 40 minutes |
Recommendations for activity/rest ratio: training times per repetition of greater than 60 Seconds and rest times of greater than 90 seconds .Each training bout should include at least six sets of rest and recovery. |
HIIT: A More Functional Way to Establish Fitness?
Research comparing HIIT to more traditional MICT/HITT or LISS training does raise some relevant questions:
1. Is it more functional to exercise using HIIT? Do our activities of daily living, and lifestyles demand an ability to shift back and forth between more intense activity and rest (HIIT), or do they solely require us to maintain an elevated heart rate for extended periods (HICT/MICT)?
2. Is HIIT a more reasonable option than MICT/HICT because individuals are more likely to commit to this type of training?
3. Is an emphasis on "training the heart to rest and recover" an important aspect of heart health? And could HIIT actually help us train for more effective heart rate variability?
4. Because HIIT has an impact on the central nervous system's control of cardiac function, is it a better form of exercise for other diagnosis which impact the central nervous system such as chronic pain and chronic fatigue?
Always Check with your health care provider before beginning any new exercise program!
Disclaimer: This BLOG is for Educational Purposes, Only. This information provided is educational and informational in nature and is made only as general information. The information does not establish a patient-provider relationship, establish a standard of care, or offer medical, dietary, or therapeutic care, advice, opinion, diagnosis, or treatment. This information does not replace independent professional or medical judgment and should not be relied upon as medical, psychological, or other professional advice of any kind or nature whatsoever. This information should not be used for diagnosing or treating any mental or physical health problem or disease. You are solely responsible for any action taken based on your interpretation of this information and you are responsible for your own health care decision-making by obtaining any necessary consultations with appropriately licensed health care professionals such as physicians and psychologists.
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