High-Intensity Interval Training: Less is More
By Ivan Blazquez, M.Ed, B.S., ACSM, NGA Pro Natural Bodybuilder, Triathlete
Weight loss, in particular, fat loss is a very common goal among many people. However, in today's fast-paced society, reaching this goal can seem quite elusive. Today more than ever, there is a high demand for a time-efficient, result-producing workout plan. The conventional way of exercise is performing aerobic exercise 3-5 days a week for at least 30-minutes and lifting weights at least 2-3 days a week for 30-60 minutes. However, this time committment may not be feasible for many. Fortunately, there is a way to exercise in less time and attain results comparable to traditional exercise. It is called high-intensity interval training (HIIT) and is quite appealing due to the wide-range of benefits it produces within such a short time investment. Although HIIT has been around for quite some time and is not a new method of training, it has recently re-emerged as top trend in the fitness industry. For those who already include HIIT as part of your exercise program, this article will not only serve as a reinforcement, but will also include perhaps a few new tidbits. As with any type of unaccustomed exercise or for those who have never heard of HIIT, it is important to consult with your physician prior to beginning interval training (9). Thereafter, it would not be inappropriate to seek further assistance from a certified fitness professional.
HIIT defined with branching applications
Although there is no universal definition of HIIT, it is generally recognized as repeated sessions of brief, intermittent exercise often performed with an "all-out" effort or intensity close to VO2 max (i.e. >/- 90% VO2 max) (8). Although this delineation is generally accepted, the term HIIT can be used loosely with broader applications. HIIT can be applied in the following ways:
1) Cardio: This is the common application of a 5-20 sec sprint followed by a 10-40 sec rest period (passive recovery) or lower intensity bout (active recovery) with any aerobic activity of choice (i.e. bike, elliptical, rower, boxing, swimming, etc.).
2) Weights: This could be also called circuit training or the superset method, but it does encompass the premise of HIIT. This method can be done on machines or free weights and involves performing 10 or more reps (i.e. 10 to as many as 30) going from exercise to exercise, with the only rest being the time it takes for one to get from one exercise to the next.
3) Bodyweight: Various informercial home-exercise programs on DVD incorporate bodyweight exercises, also known as calesthenics, as a form of HIIT. The purpose is to gets results in a short period of time for many who struggle with maintaining a regular exercise routine. This form of training is very effective and can be very humbling as one's own bodyweight not only provides the resistance, but can also become a wake-up call as to one maybe needing to lose those few extra pounds.
4) Combinations or Stacking: These methods can be mixed to provide different results too. For example, one can perform a set of 10 pull-ups, followed with 30- jumping jacks, do 30-push-ups, then do 1-minute on the rower and so on. Another scenario could be performing a one set of 10 reps of dumbbell chest press followed by 10 stationary lunges with just one's bodyweight.
5) Cross-Fit: A newer version of HIIT in which a mixture of any kind of physical activity is performed for time, distance and/or reps. Essentially, cross-fit training is a collection of bodyweight, resistance training and cardio exercises and in some cases, some exercises include a combination of cardio and resistance exercise. What makes cross-fit unique is that it seems that the basis for the exercises selected is prefaced on functional and metabolically-demanding movements. It is truly a new breed of fitness and I personally find it to be very beneficial in overall health, fitness, function and exercise time-management.
HIIT does not have to be limited to being an "all-out effort" at all. In many cases, it is dismissed as being only for elite athletes (9). However, the basic premise of alternating higher intensity and lower intensity periods of exercise can be applied to almost any level of initial fitness (9). Additionally, interval training is often based on subjective effort and does not necessitate working out at a specific heart rate or speed (9). So while intervals may mean all-out running sprints for people with high levels of fitness, they could simply mean a brisk walk for others (9). In a sense, HIIT is simply a way to get people to exercise a little harder. Just about any kind of physical activity can turn into interval training based on the way the physical activity is performed.
In exercise physiology, the assessment of caloric expenditure is classified as METS. The term MET is a commonly used acronym that stands for "Metabolic Equivalent" and it is the ratio of work metabolic rate to resting metabolic rate (1, 7). This unit of measurement can sometimes be found on bikes, treadmills, ellipticals, etc. Essentially, 1 MET is the energy expenditure of a person at rest sitting quitely and is defined as 3.5 milliliters of oxygen, per kilogram of bodyweight, per minute (ml/kg/min). For example, if an activity requires 10 METS, the energy requirement in oxygen consumption terms would be 35 ml/kg/min. So how do we figure out calories burned? There are a few math steps to get to calories burned, but keep in mind that with this being said, these are only estimates at best, but they do give ball-park figures. If a 160 lb person exercises at 35 ml/kg/min for 20-minutes, a way to figure out calories burned would be as follows:
Step 1: Convert person's bodyweight to kilograms. 160 lb/2.2 kg = 72.72 kg
Step 2: Multiply person's bodyweight in kilograms to 35 ml/kg/min (this is the constant value of person's exercising metabolic rate). 72.72 kg x 35 = 2545.2 ml/min
Step 3: Since the metabolic conversion of 1 liter of oxygen is 5 calories, we divide 2545.2 ml/min by 1000 ml/min. This converts 2545.2 ml/min to 2.5452 L/min.
Step 4: Recall 1 liter of oxygen consumption is equal to 5 calories. Now we multiply 2.5452 L/min by 5 to get 12.726 calories per minute.
Step 5: In 20-minutes of exercise at this work rate of 12.726 calories per minute, this person will have burned roughly 254.52 calories. If this person exercised at this rate for 1-hour, this would be 763.56 calories per hour.
Not a bad exercise work rate at all. However, if this same person were to simply incorporate ten 30-sec intervals at a workrate of 50 ml/kg/min, while the remaining 15-minutes were performed at 35 ml/kg/min, the caloric rate would increase to 845.37 calories per hour. Essentially, just working a little harder in short intervals will add up in the end in regards to total calories burned. Not to mention, there are several other factors that may even increase this value further. For instance, there are the following factors of HIIT training that were unaccounted for: Excess post-exercise oxygen consumption (EPOC), greater glyocogen degradation thereby creating greater reliance on fat, exercise economy of speeding up and slowing down, exercise economy of changing leverage during bodyweight exercise, increase in fitness level thereby making one a better fat-oxidizer, etc. Without going into depth of discussion, these are just some of the factors that make HIIT unique in regards to boosting fat loss.
In fact, it is the high intensity exercise motto that many home exercise informercials have used and tout participants of their program can burn up to 800-1000 calories per hour! Well, of course the two biggest factors determining work rate are the difficulty of the exercise being performed and the person's bodyweight. As a certified fitness professional, metabolic work rate is an important element in exercise programming design for the common goals of many. However, as often the case, there are caveats. The first would be a prior health and exercise history screening outlining each individual's boundaries. Some clients may not be able to tolerate high-impact activities such as running or plyometrics. However, this is where the creativity and craft of a qualified fitness professional becomes emminent. The creativity to incorporate HIIT into lower-impact activities such as spinning, swimming or bodyweight exercises can broaden the spectrum and give more opportunities for those who may not be able to perform higher-impact activities. This is the science and benefit of having a fitness professional on your side to guide. Fitness professionals know that calorically expensive activites are the way to go in regards to weight loss and fitting in those skinny jeans. However, with the guidance of a certified personal trainer, there can be an accommodation for various orthopedic issues and other ways can be found to burn those calories at a high rate without incurring unwanted muscle aches or injuries. With the guidance of a certified personal trainer, the list of exercises are endless and this makes the workouts fun due to the constant mixture of exercises and workout routines.
Safety of HIIT: Special Populations
Studies have begun to investigate HIIT training in supervised high-risk populations such as patients with heart disease (30), diabetes (11) and hypertension (12) and have found it to be a relatively safe and effective training strategy (17, 19, 21, 26, 28). In fact, research has also shown HIIT to be beneficial for cholesterol management and/or prevention (29). Some studies have even shown HIIT to boost our good cholesterol (HDL) (16, 20).
It has also been found to be an effective tool for controlling and/or preventing hypertension (6, 12, 16). The benefits are multi-dimensional but are based on improved exercise capacity, which in it of itself has been shown to have a strong inverse and graded association to all-cause mortality in apparently healthy individuals (3) as well as prehypertensive (15) and hypertensive individuals (6, 14). In other words, the higher one's fitness level, the lower the risks are of cardiovascular disease and other metabolic disorders. We've probably heard the saying, "Survival of the fittest," but in a "fitness sense," it also seems to hold true. Additionally, there is the profound post-exercise hypotensive effect that has also been illustrated to occur with HIIT (22).
Moreover, in these studies in which HIIT was compared to conventional aerobic exercise, it was reported that in the HIIT interventions, greater improvements in health and fitness occurred compared to the conventional aerobic exercise groups (9, 24, 26, 30). Another study showed that while HIIT has comparable health benefits compared to traditional aerobic exercise, it also has additive effects (Ciolac et al., 2010; 12). It was found that both conventional aerobic and interval exercise were beneficial for blood pressure control, but only interval training reduced arterial stiffness (12).
HIIT: Effects on Fat-Loss and Health and Fitness
Having read through a lot of the research on HIIT, it sounds almost too good to be true with how it actually stimulates an anabolic environment for muscle while concurrently promoting enhanced fat-burning capability and activity! One such study was undertaken in nineteen obese individuals and it was found that when following a carbohydrate-reduced, energy-restricted diet along with performing HIIT, only the diet + HIIT group preserved muscle mass, while VO2 peak was also increased only in this group (23). While it has been suggested that HIIT may not be as ideal for weight-loss due to the short-lived nature of the exercise session, this can be true in some cases, but the reality is, everyone is different. That being said, HIIT can be incorporated by anybody and can be modified if necessary (18) while still providing ample results. In fact, this was shown to be true in one study that looked at a reduced-exertion HIIT (18). In this study, subjects performed brief sprints of 10-20-s and maintained a low rating of perceived exertion, yet saw improvements in insulin sensitivity and aerobic capacity (18). In terms of fat-loss, studies have shown that HIIT can induce greater fat loss (25, 27, 31) and comparable health benefits compared to traditional aerobic exercise (10). In fact, one study showed that despite less calories being burned, those who performed HIIT lost more body fat compared to those performing traditional endurance training (27). Regular HIIT training has been shown to significantly increase both aerobic and anaerobic fitness, while significantly lowering insulin resustance (4). HIIT training has also been shown to promote a number of skeletal muscle adaptations that result in enhanced fat oxidation and improved glucose tolerance (4). In fact, there was a keynote address at my organization's health and fitness summit titled "Regular to Ripped: High Intensity Interval Training" (5). While I unfortunately was unable to attend, I'm sure this was a great presentation (5) and I just love the title!
Overall, research has also shown that HIIT can boost aerobic fitness level more effectively than traditional aerobic exercise thereby conveying desirable cardiovascular benefits (13, 24). Essentially, with the addition of 1-2 HIIT workouts a week or even once every other week within a regular exercise regimen, one can improve performance in traditional aerobic exercise and also aid in his/her own fat-loss and health-promoting efforts. This time-efficient training strategy can be used to expedite weight loss and reduce metabolic risk factors for those who otherwise would not be able to adhere to a time consuming traditional exercise regimen (2).
While HIIT is not a new training method, it has re-ignited in the fitness industry. Disregarding the recent fitness industry's biased inclination towards HIIT, but viewing HIIT in an unbiased manner, it is truly a fantastic method of training when used appropriately. This would include incorporating HIIT in moderation (i.e. 1 or 2 times per week) and there being proper supervision (i.e. medical personnal) and guidance in higher-risk populations. That said, HIIT should not be limited to one application of simply performing a common aerobic exercise with repeated short-duration all-out efforts followed by short rest periods. The term can be used loosely in reference to metabolically-challenging activities that encompass higher intensity work bouts or efforts such as cross-training and/or cross-fit type workouts. Simply put, getting off the treadmill, bike or elliptical and starting to use one's own bodyweight in training or just picking up the pace a little bit during a weight training workout can also be classified as forms of HIIT. For instance, it can be viewed as even going through a circuit of exercises, in which each exercise is viewed as an work interval and the time needed to get to that next exercise would be the rest interval. Now of course, common sense would be to take as much rest as needed based on each person's capabilities as well as working at an intensity that is tolerable, but a little higher than normally accustomed to. This is also known as overload (7), a basic physiological principle that is well-known among fitness professionals and can be applied to any form of physical activity. In a sense, the variety through the interchangeable intensity as well as the constant mixture of exercises during a workout are some of the benefits that working with a fitness professional can entail. This is what makes HIIT fun and keeps things interesting due to the change that inherently occurs within this form of exercise. Any goal worth achieving not only takes time, but it also requires a meaningful effort. The important thing to remember is that any goal worth achieving not only takes time, but it also requires a meaningful effort. More often than not, the answer to achieving one’s fitness goals are not easier said than done, but better done than said.
The information provided in this article is for educational and informational purposes only and does not serve as a replacement to care provided by your own personal health care team or physician. The author does not render or provide medical advice, and no individual should make any medical decisions or change their health behavior based on information provided here. Reliance on any information provided by the author is solely at your own risk. The author accepts no responsibility for materials contained in the article and will not be liable for any direct, indirect, consequential, special, exemplary, or other damages arising from the use of information contained in this or other publications. Copyright Ivan Blazquez, 2011. No part of this publication may be reproduced or transmitted in any form without the prior written permission of the copyright holder and author of this publication.
Oliver, GD, Stone, AJ, Wyman, JW, Blazquez, IN. (2012). Muscle activation of the torso during the modified razor curl hamstring exercise, International Journal of Sports Physical Therapy, 7(1), 49-57.
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The information provided in this article is for educational and informational purposes only and does not serve as a replacement to care provided by your own personal health care team or physician. The author does not render or provide medical advice, and no individual should make any medical decisions or change their health behavior based on information provided here. Reliance on any information provided by the author is solely at your own risk. The author accepts no responsibility for materials contained in the article and will not be liable for any direct, indirect, consequential, special, exemplary, or other damages arising from the use of information contained in this or other publications. Copyright Ivan Blazquez, 2012. No part of this publication may be reproduced or transmitted in any form without the prior written permission of the copyright holder and author of this publication.