High intensity interval training, otherwise known as “HIIT”, is a fairly broad term for a certain way to exercise. In its simplest definition, it is exactly what it suggests, which are intervals of high intensity followed by intervals of lower intensity. Now, this is quite broad so what exactly does this mean for you? Well, like with anything health, fitness and dietary related, we all have individual differences which affect how we might go about incorporating some of these things into our lives.
HIIT training has been popular for a couple decades now and can be performed in many ways. The basic idea is to have relatively brief intervals of very intense training that elevate heart rate (usually up to about 80% of max heart rate—max HR is 220 minus age) which increases lactic acid and can induce muscular and/or cardiorespiratory fatigue rather quickly. It is typically regarded as anaerobic (without oxygen) training, which is a contrast to aerobic training (walking, jogging, or other low to moderate intensity cardio-based activities) although it is a bit of a combination of the two. HIIT can be done as part of weight training, body weight training or just about any “cardio” based activities such as running, biking or swimming.
- Riding an exercise bike with 60-second-high-intensity intervals followed by 2 minutes of rest. This is repeated for several repetitions. This could be part of a spin class where there are periods of fast, intense work followed by a period of recovery.
- “Sprinting” 100 meters at a track followed by walking for a period of time to recover
- “Bodypump” or other bootcamp-like activities where there are these intense periods of activity followed by a rest period
- Full body workouts broken down into intervals for a certain periods of time
- Swimming one length of a pool as hard as possible followed by an easy recovery lap
- For people less conditioned or unable to do as vigorous activity it might look something like walking faster for a period of time followed by a slower walk for recovery.
- Tabata intervals are a specific type of HIIT characterized by 20 second intense intervals followed by 10 seconds rest for a total of 8 intervals which takes 4 minutes to complete
Well, there are a couple of compelling reasons to consider incorporating some form of HIIT training into your program.
- HIIT workouts are short (at least they should be) but very effective. In a matter of a few minutes you can have a great fat burning AND muscle building workout compared to spending a monotonous 45 minutes on a treadmill. This is very appealing to busy, working people looking for the best “bang for the buck”.
- Some research suggests that HIIT “cardio” is overall much more effective than regular steady state cardio (think jogging, running, treadmill-type boring stuff). Not only is it likely just as effective, or better, at improving V02 max (this is a measure of cardiorespiratory fitness) but HIIT training has all sorts of long-lasting fat burning and muscle building effects that last as long as 24 hours after the activity is done! In addition, it helps to control blood sugar better and can make you more insulin sensitive (this is a good thing). This is due to the stimulation of various hormones as a result of the HIIT workout. The slow, steady state cardio can burn fat but it also can be catabolic, meaning it breaks down muscle tissue (not a good thing) whereas HIIT tends to be anabolic (build muscle tissue) which, of course, is a good thing. The most effective example which helps explain the difference between HIIT and steady state cardio is the comparison of sprinters to marathon runners. Sprinters are muscular and powerful with chiseled bodies. Marathon runners tend to be skinny, oftentimes “skinny-fat” with very little muscle and oftentimes not much muscle definition. I know who’d I’d rather look like!
What NOT to do:
- If you are not in shape or have or might have any underlying health conditions (such as heart issues) or other orthopedic issues, don’t start a HIIT program until you are medically cleared to do so. Assuming you are healthy, you will need to first start a basic exercise program for several weeks before incorporating HIIT into your program as it can be very taxing on the body, especially in someone who is not in good exercise shape.
- Do NOT overdo HIIT. Too many people have the mentality, “If a little is good, a lot must be better”. Well, in the case of HIIT this is not true, especially for the average adult who works and has a family. All exercise induces stress on the body. The benefits of exercise happens during recovery. HIIT is no exception. In fact, HIIT induces more stress on the body than other forms of exercise which is why it needs to be done less frequently. Doing HIIT too often can keep the body in a state of stress and trigger the release of cortisol (stress hormone) for prolonged periods of time which then can have a negative effect on health and recovery. Cortisol released for SHORT periods of time in response to stress is NORMAL, but it’s important to avoid PROLONGED stimulation of cortisol. Too much HIIT, plus not sleeping enough, plus bad eating, plus work and family stress can all lead to too much cortisol release as well as other inflammatory hormones. When first starting HIIT training I would just try for once a week for a few weeks with an ultimate goal of 2 HIIT workouts a week for 20 minutes max, maybe 30 minutes if very well-conditioned. This should be plenty for the average adult. There is research out there suggesting any more than 30-40 minutes of HIIT a week can have negative side effects.
- Don’t do HIIT during periods of extreme stress, illness or lack of sleep. As I mentioned, HIIT is a stressor on the body. This, of course, is expected and why HIIT is so beneficial. BUT, if your recovery ability is impaired due to extreme stress, illness or lack of sleep, HIIT might do more harm than good as it is just adding more stress to an already compromised situation. As I mentioned before, the benefits of HIIT, and all forms of exercise, takes place during the recovery period. If you are compromised for any reason then your ability to recover will be impaired and the stress hormones will be out of whack and what was meant to be a good thing is now a bad thing.
- Consider doing HIIT on an empty stomach in the morning for maximum fat-burning effect. Although there is somewhat conflicting scientific evidence to support this, many health and fitness experts, myself included, recommend this strategy. If you are doing HIIT on an empty stomach and are following a fairly low-carb diet then the logic is you will more easily tap into your fat stores than if you already had calories in your body from eating. My own personal experience is that fasted HIIT is superior to doing HIIT after consuming calories. That being said, do what works for you. If your schedule only allows you to workout later in the day then that is fine, don’t stress about things you cannot control.
- After a HIIT workout, try and avoid consuming any calories for at least an hour as this might also help to maximize fat burning and positive hormone effects. Once calories are consumed it starts to “blunt” some of the positive hormone effects of HIIT training.
- Do not sacrifice sleep to get up and do HIIT (or any other kind of exercise). As someone who has previously sacrificed sleep in the name of fitness, I do not recommend this! As good as exercise is for the body, sleep is better. If you are cutting sleep short to get up and be to Bootcamp by 5:30 am you could be doing more harm than good. Lack of sleep is stressful on the body (in a bad way). You force yourself to Bootcamp where you endure more stress (in this situation, probably negative). You rush home to get the kids going and get yourself ready for work or whatever else you are doing that day and it’s run, run, run. Stress, stress and more stress. This is why so many people workout but never make any progress. If your body is in a constant state of stress it will not burn fat. Either find another time to workout so your sleep is not impaired or go to bed earlier to ensure you get 7-8 quality hours of sleep.
- Eat well, sleep well, manage stress for maximum results: to piggyback off of the previous point, it’s important to address and optimize each of the 4 key elements of health to give yourself the best shot at being lean, strong and healthy. HIIT by itself is useless if you aren’t incorporating an overall healthy lifestyle. Those 4 key elements are nutrition, sleep, stress management and movement, click here to read more: https://parnhamhealth.com/the-4-key-elements/
Thanks for reading. I know I didn’t cover every aspect or answer every question about HIIT. Thanks for reading and feel free to comment or ask questions!
Here’s a link to some decent ideas for HIIT for beginners: https://blog.myfitnesspal.com/4-week-hiit-plan-beginners/