Table of Contents
- 1 High intensity interval training (HIIT)
- 2 Why Does HIIT Work?
- 4 What Makes HIIT Different from Other Types of Exercise?
- 5 HIIT Interval Training Workouts
- 6 Who Benefits From Interval Training?
- 7 Conclusion
High intensity interval training (HIIT)
HIIT interval training is suitable for just about everyone, from elite athletes to those who have not exercised in years and may be struggling with serious health issues such as obesity, heart disease or type 2 diabetes.
HIIT consists of alternating periods of intense exercise with periods of lower-intensity effort for recovery. It means less time exercising while providing the same or greater health benefits than endurance training.
High intensity workouts can be done in the comfort of your home with little or no equipment in a 10-20 minute session. So far, it has been used almost exclusively by elite athletes but there is mounting scientific evidence that anyone, no matter their fitness level or health concerns, can benefit.
Why Does HIIT Work?
One of the major benefits of exercise is that it triggers changes in the heart muscle; it thickens and expands the left ventricle improving heart function, which improves fitness.
Fitness level can be measured by the volume of oxygen you can consume while exercising at your maximum capacity. Commonly called maximal aerobic capacity, VO2 max is the maximum amount of oxygen that a person can use during intense exercise. It is considered the best indicator of a person’s cardiovascular fitness and aerobic endurance.
Recent studies have shown that HIIT is significantly better than endurance training for improving VO2max. http://www.ncbi.nlm.nih.gov/pubmed/22648463 (used later for weight loss) In other words, HIIT is the fastest way to get fit. Being fit may be even more important than we think because lack of fitness may be the single biggest contributing cause of death.
In a large observational study of 40,842 men and 12,943 women over a six year period, low cardiorespiratory fitness (Low CRF), which means being out of shape, contributed more to death amongst men and women than obesity, high cholesterol and diabetes combined. Only hypertension amongst men came close to equalling the negative impact of simply being out of shape. http://bjsm.bmj.com/content/43/1/1.full
A 2014 randomized study of 112 adults concluded that the higher the intensity level of the exercise, the bigger the improvement in fitness level. http://www.jsams.org/article/S1440-2440%2813%2900153-9/abstract
A 2015 randomized study of 90 inactive adults performed in a real world gym setting proved that those who engaged in HIIT workouts became fitter while spending less time at the gym, and were more likely to stick with it than those engaged in more traditional endurance workouts.
Amazingly, trying HIIT for just one session is enough to improve obesity related factors. One 2012 study of ten obese men found that having them engage in four 30-second sprints with four minutes of recovery in between improved their glucose tolerance and the results lasted for at least 24 hours. http://www.sciencedirect.com/science/article/pii/S1728869X12000342 (used above) A 2013 randomized study involving ten obese/overweight men found that a single session of four sprints was enough to show improvement in insulin sensitivity and fat oxidation.
What Makes HIIT Different from Other Types of Exercise?
High-intensity intervals work both your aerobic and anaerobic energy systems by pushing past the upper end of your aerobic threshold (this is age and fitness dependent). Meanwhile, the recovery periods allow your system to replenish your anaerobic energy system.
After HIIT your oxygen use (VO2) remains elevated for a while. This afterburn effect is known as EPOC (post-exercise energy consumption) and is an oxygen debt involving the amount of oxygen needed to restore your body to its normal, resting level of metabolic function. This is why you continue to burn calories long after you finish your workout.
The higher the intensity of the workout the more anaerobic energy is required, increasing the need for oxygen after the workout, enhancing the EPOC effect. This has been proven in several randomized trials, such as this 2015 trial involving 20 women.
HIIT Interval Training Workouts
Even though HIIT can work for just about everyone, if you have any doubts, speak to a healthcare provider about whether it is right for you and consider taking some personal training to learn how to do it properly.*
Always warm up and cool down for at least five minutes before and after each session. If you experience chest pain or breathing difficulties during your workout, stop doing all high-intensity portions and cool down by walking around before stopping your activity. If symptoms persist, seek medical assistance. Even though the goal is to work to exhaustion and you want to feel breathless and fatigued as you progress through the workout, you still need to be in control.
The secret (tough part) of HIIT is to work hard during the intense intervals. The goal is to work out at approximately 90 percent of your maximum, which trains your body to work anaerobically, which helps your body to become more efficient at producing and using energy.
An effective way to know that you are working out at the appropriate level is to use an online heart rate calculator. http://www.active.com/fitness/calculators/heartrate
Different Types of Interval Training Workouts
Interval training can be broken down into two broad categories, one for serious athletes and the other for the rest of us. Even though interval training is not just for athletes, it is physically demanding and in particular the more advanced versions require care.
Below are three examples: a beginner version, an intermediate version and an advanced version.
1 – The Interval-Walking Program
This is an excellent beginner’s program and consists of five or more sets of three minutes of low-intensity walking followed by fast walking for three minutes three to five times per week. The low intensity walking should be a bit faster than a stroll (40% effort) and the higher intensity walking should be at a minimum of 70-80 percent of maximum effort. Over time you can increase the number of sets and intensity. An excellent way to increase the intensity is to walk up a hill.
2 – Power Intervals:
This is a versatile version that allows you to go all the way from low-intermediate to advanced.
It is recommended that you start with a 30/90 ratio, 30 seconds of high intensity activity with 90 seconds of active rest recovery.
One of the best parts about this is that it can be done almost anywhere. You can do it on a track or side road by sprinting/walking, in a swimming pool or on a wide variety of exercise machines. Interestingly, if you choose to sprint/walk, the distance you cover in 30 seconds of sprinting is about the same as what you cover in 90 seconds of walking. You only have to time it once or twice and you are on your way. Start with six sets and try to work up to eight sets for a 16 minute “power” workout.
Keep in mind that HIIT is about intensity and not endurance. Therefore it is more important to keep up the intensity with fewer sets.
Over time you can increase the intensity by gradually diminishing the amount of recovery time and having a 30/60 ratio or even work up to a very advanced level of 30/30.
3 – Tabata Protocol:
This is one of the better known methods, used by many elite athletes.
It involves 30 second sets, consisting of 20 seconds of high intensity work with 10 seconds of rest. These 30 second sets are repeated eight times for a total of four minutes “superset”. During the 10 second rest periods it is recommended that you stop moving. You can do anywhere from one to three “supersets” with two to three minutes of rest between. For more information please go here. (http://www.bodybuilding.com/fun/the-real-tabata-brutal-circuit-from-the-protocols-inventor.html)
Who Benefits From Interval Training?
There is no doubt that HIIT is a very effective part of elite athletic training and its effectiveness has been demonstrated by numerous studies. http://www.ncbi.nlm.nih.gov/pubmed/17414804/
What is not well known is how effective HIIT is for the rest of us. There is a growing number of large randomized studies showing that it is very effective for those suffering from obesity and debilitating illnesses such as heart disease and type 2 diabetes. It appears that it may even impact longevity. http://circ.ahajournals.org/cgi/content/meeting_abstract/126/21_MeetingAbstracts/A18220
Overweight or Obese
Exercise and diet are the key components for weight loss. Typically, moderate intensity exercise is recommended for overweight or obese individuals because it is believed to be the safer option.
Recent studies have disproved this idea. It has been shown that HIIT is more effective than moderate exercise for weight loss. http://www.ncbi.nlm.nih.gov/pubmed/22648463 HIIT has been shown to be superior for improving glucose tolerance, lowering blood pressure, http://www.ncbi.nlm.nih.gov/pubmed/26293124,http://www.sciencedirect.com/science/article/pii/S1728869X12000342 improving cardiorespiratory fitness, http://www.ncbi.nlm.nih.gov/pubmed/26089322 and being a safer and better tolerated option. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4619258/
Type 2 Diabetes
Studies have shown that HIIT leads to rapid improvements in glucose control http://jap.physiology.org/content/111/6/1554.short
and cardiovascular health in individuals with type 2 diabetes.
A 2003 randomized study involving 16 middle aged overweight men with type 2 diabetes participating in an eight week HIIT program had a decrease of 44 percent of abdominal fat, a 24 percent increase in mid-thigh muscle and a 58 percent improvement in insulin sensitivity.
Numerous studies have shown that HIIT is safe, well tolerated and superior to moderate exercise for patients with heart disease.
A very large 2012 study of 4,846 patients with coronary heart disease clearly demonstrated that high-intensity exercise provides greater health benefits than moderate-intensity exercise for patients with coronary heart disease, and most importantly is safe to do.
Studies have shown that HIIT is superior to moderate exercise for a number of heart patients including: chronic heart failure, http://circ.ahajournals.org/content/115/24/3086.long
myocardial infarction, http://cre.sagepub.com/content/26/1/33 heart transplant patients, http://www.ncbi.nlm.nih.gov/pubmed/25135383 metabolic syndrome, http://circ.ahajournals.org/content/118/4/346 myocardial infarction, http://cre.sagepub.com/content/26/1/33 ischaemic heart failure http://www.ncbi.nlm.nih.gov/pubmed/26667151 and coronary heart disease. http://www.hindawi.com/journals/tswj/2015/192479/
In addition to helping with so many types of heart disease it has also been shown that the greater the intensity of the exercise the better. A 2014 study of 112 coronary heart patients had them engage in high-intensity interval training at three different intensity levels of <88%, 88–92%, and >92% over a 12 week period. There were health improvement in all three groups but the higher the intensity of the exercise the bigger the improvements.
To top it all off, a 2016 randomized study of 19 patients with ischaemic heart failure showed that after 12 weeks of HIIT there was significant improvement with regard to the symptoms of anxiety and depression versus no improvement with moderate exercise.
Exercise has numerous benefits for cardiac patients, including weight loss. These benefits are amplified with HIIT, which is also easier to stick with than traditional cardio workouts.
High intensity interval training stirs the pot in the body, in effect, forcing it to release more hormones to burn fat. It is easier on the joints than endurance training because you are spending much less time exercising. It can be performed almost anywhere using a variety of equipment such as a treadmill, bike and elliptical machine, or no equipment at all by sprinting/running, swimming, body-weight exercises and much more. Simply walking up a hill at timed intervals of varied intensity can do the trick!
HIIT workouts get your heart rate up and improves your cardiovascular fitness level while burning more fat and calories in a fraction of the time you would spend doing steady-state cardio.
If you have not been exercising regularly, or have a chronic health condition, numerous studies have shown that you can still benefit from a high intensity workout. However, it is always a good idea to check with a healthcare professional before commencing any workout program.
*This is a good idea for many reasons, not the least of which is that a condition (not rare) called ‘hypertrophy of the right ventricle’ would be a pre-existing condition that might preclude doing this kind of thing. It develops for a number of reasons, but long residence at high altitude creates it in almost everyone who lives there–basically it’s part of the physiological and somatic adaptation to life in hypoxic conditions. I’m sure most of the work done with people in the trials we are citing are done with individuals who don’t have that, and don’t live there–but a large segment of the world’s population does live there.