High Intensity Interval Training (HIIT) - What You Should Know.
It would be ridiculous to claim that I invented HIIT. But yours truly are one of the earliest advocates of this training method and have implemented it in my clients' exercise routines (both strength and cardio versions) right from the beginning when I developed my Body-Transformation-Programs in 1998. Hence I can qualify myself a subject matter expert in this popular training method.
The real origin of HIIT
Despite all the buzz in recent years, HIIT is not really a new concept, in fact it has been around for about for several decades now. The origins of HIIT training can be traced back to 1912 where it was used by the best Olympic runners at that time, usually the Scandinavian athletes, in their own training. The true researchers of HIIT are Saltin and Astrand who published their first study in 1959 and all of the subsequent HIIT techniques from then on were, more or less, borrowed from their original research.
How is HIIT done
HIIT exercise sessions are typically performed with 'cardio' type exercises (e.g. running, cycling). It consists of:
a warm up period, followed by
several cycles of high-intensity (hard) exercise separated by low-medium intensity (easy) exercise for recovery, then
a cool down period.
Typically, sessions last under 30 minutes, with times varying based on a participant's current fitness level. Essentially, it means a short workout of alternating easy and hard works.
HIIT are now used in strength workouts too.
My personal HIIT testing with great successes
I had come across this in a fitness journal (name forgotten) somewhere in 1992. The enlightening article was in line of my thought about certain exercise physiological principle that no one was applying at that time.
Everyone followed flawed unproductive exercise routines found in fitness magazines which often are not fully grounded in science.
The newly discovered exercise theory got me very intrigued and decided to put it to test through some sample routines. True to the article and to my delight, I had achieved very impressive results from them. I had lost a significant amount of bodyfat and also skyrocketed my cardiovascular fitness within a short span of time. I also attributed it to my 3rd place win in National Bodybuilding (junior) in 1992 by combining it with some specialised strength training and of course, mindful nutritional intake. Also bear in mind that most bodybuilders then were probably training 6-7 times a week, with minimum 2 hours each session, plus a heavy dose of illegal anabolic stuff (steroids that is). As for me, I trained naturally with nothing more than 3 weekly sessions of hourly workouts of HIIT and Strength Training.
In the same year (1992), I got enlisted into the Army into a specialised unit that required greater fitness level than normal units. The timing needed for 2.4km running component was below 9.15min (instead of typical 9.45min) in order to secure a 'Gold' for the army fitness test . During the 2.5 years stint there, everyone had to clear several such tests at regular intervals. And I had on all occasions gotten gold with running timings of between 8.15min and 8.45min, quite impressive feats considering:
I only did a couple (quite literally 2-3x) of HIIT sessions before all the tests.
I had a muscular built (how many bodybuilders you know can really run not to mention, excel at it? A few fellow bodybuilders of my age I knew then couldn't survive one lap around the stadium of non-stop slow jog) and
I am never a runner (genetically, passion or otherwise). My ex army buddies can attest to these facts. I was nicknamed 'Baby Hulk' for my built and 'PTI ' (physical training instructor) for my generally fitness.
About Tabata Protocol and CrossFit - They helped to popularise HIIT
A fellow advocate and a very reputable early researcher of interval training, Professor Izumi Tabata (田畑泉), who created the highly popular Tabata training protocol (a form of HIIT), only came to scene in 1996. CrossFit is a another branded regime that incorporate HIIT along with other exercises in their their training routines, it only started in 2000. So you can see I got into HIIT even before these 2 hugely popular HIIT household names (Tabata and Crossift) started to appear.
Tabata and his colleagues (1996) conducted a research that compared moderate-intensity continuous training at 70% of maximal oxygen consumption (VO2max) for 60 minutes, with HIIT conducted at 170% of VO2max. HIIT consisted of eight, 20-second all-out exercise bouts followed by 10 seconds of rest for a total of 4 minutes of exercise. The study found that HIIT improved aerobic capacity to a similar degree as moderate-intensity continuous training, but also resulted in a 28% increase in anaerobic capacity.
My Master's Degree research in HIIT and connection with my business: Fitness Tutor
HIIT was one of the primary reasons why I became a personal trainer and started my personal fitness training business in Singapore (1998) when I realised that this form of training would have the potential to offer far better results for my clients, as compared to what the others were doing at that time (i.e. promoting low-intensity method, eg doing slow walk on treadmill and doing aerobic workouts as the best way to 'burn-fat'. It was a widespread flawed training method, although that was based on a legitimate exercise physiological fact).
In 1999/2000, I got enrolled in a Master's programme in the science of Exercise and Nutrition. During this period, I took the opportunity to further my understanding the science and art of HIIT. I physically went to many university libraries, visited online ones, and dug out all relevant books and journals, subscribed to some, and devoured all the information like a hungry wolf.
I then designed my version HIIT protocol and tested it some clients and friends whom I had recruited for this research purpose. The outcome was very positive, which I had expected. I collected the data, analysed them statistically, and documented them into the thesis for my final year project (see below). Note: Chester University was a college of University of Liverpool at the time.
During this period, I had also written several pro-high intensity articles like 'Anaerobic or Aerobic - which is the better way for weight loss' (published on Ministry Of Health's Healthy Lifestyle Portal).
Subsequently in 2005, I got Certified as 'Lifestyle and Weight Management Specialist' by American Council on Exercise in which the programme also strongly promoted the use of HIIT for fitness and fat-loss. Till today, I am still fine-tuning it because there are still many ways to make it even better.
Fast forward to recent years, like fashion, a wave of HIIT Tsumai suddenly swept the fitness industry out of the blue. Within a couple of years everyone was raving about it. Magazines started splashing articles about it and its benefits. Exercisers switched their usual training mode from low to high-intensity. Every gym I know started to push HIIT to therir members. Fellow fitness trainers, started to jump on the bandwagon and claimed to be experts. Some of these were the same guys who had, not too long ago, strongly opposed the use of HIIT and defended their preferred low-intensity training methods or mocked at me during the earlier years when I preached about HIIT. Some even called it 'ridicules training method'. Imagine my vexation.
Let bygones be bygones, I hope these newly converted 'experts' do know what they are doing stay true to the principles of HIIT. However, judging from the way they have conducted the training on their clients and themselves, I cringed. Almost all of them are doing it wrong in some aspects. They seem to have completely no clue what HIIT is all about. It's either just random exercises put together or they just blindly followed the videos found on the internet which in my book, spells disasters in the making. The customised training part is completely missing in the equation. They have switched from misapplications of a valid scientific theory to misutilization of another great one. What they do would either not produce any desired result and/or may cause serious injuries to the exercisers
I will shed some light on how to and how not to do HIIT.
First, let's talk about the Benefits of HIIT
There are hundreds, if not thousands, of studies pointing to the effectiveness's and benefits of HIIT. Here are just some of them:
Improved health - Interval training substantially improved a number of metabolic and cardiovascular risk factors, and a whole list of others.
Increased endurance — Interval training trains your heart to pump more blood to the muscles and it trains your muscles to extract oxygen from it more efficiently, making all your other workouts easier to handle
More efficient workouts — If you have limited time, such workouts are superb time savers, allowing you to accomplish more in a short period of time.
Greater fuel efficiency — This type of training systematically taps the body’s different energy systems (phosphagen, glycolytic, and mitochondrial respiration), thus effectively burning fat and carbohydrates.
Better performance — Working at high intensities raises your lactate threshold and improves your performance
Reduced risk of injury — Because you're varying intensity, you may be able to avoid overuse injuries or overdoing it with longer workouts
More fun - Interval workouts have much more variety than other workouts, making them less tedious
Fat loss and muscle gain - Studies show that interval training, may burn more fat and build muscles, if you work hard enough, can increase afterburn. Look at the bodies (compare their muscle to fat ratio) of sprinter (who uses interval training) and that of a long-distance runner (who uses traditional low-intensity steady state training) and you can get the picture.
Balanced of hormones - It can boost testosterone, reduce estrogen etc along with other favourable changes in hormones
Now comes the interesting part...
Unbeknown to many, yes many so-called 'HIIT experts' even, there are actually two kinds of HIIT:
Performance Interval Training (PIT) and Fitness Interval Training (FIT). Can consider this as a modified HIIT.
PIT, as the name implies, is typically geared towards well-trained athletes who are seeking to enhance their performance for sports. Most scientific protocols (e.g. Tabata) use this approach for research and programming. It involves the exercisers to push themselves during the 'high-intensity'/hard phase near to/to their absolute maximum limit. Apparently, this is very demanding, requires a lot of mental and physical strength, and may necessitate the standby of the puke bucket.
Such interval training , I repeat, is strongly recommended only for the professional/highly motivated/seasoned exercisers, and NOT for the average 'just-want-to-keep-fit' Joe.
FIT, on the other hand, is highly recommended for most gym users. For this form of interval training, as you would have guessed, the exercisers need not push themselves to the extreme during the 'hard' phase. They just need to periodically increase intensity throughout the workout. Such increase in intensity is capped when the lactate threshold (slight breathless is felt) is reached, after which the intensity is decreased. In a nut shell, the high intensity here is actually not very high, as compared to the PIT. This picture may explain more.
But everyone one is doing PIT
Many HIIT practiced in many gyms are often done in similar fashion as PIT, pushing the exercisers to the absolute limits, disregarding the capabilities and/ goals of the exercisers as stated above. So much for 'tailoring' a program. In fact, one can often see slogans like 'go hard or go home' plastered all over the place, prompting the exercisers to go as hard as possible, else it's deemed as a wasted workout. By doing so, they do not realise they could be doing more harm than good. This is akin to eating a buffet - eat as much as you can to get the money worth. It just doesn't work that way.
A workout is a workout, a half-assed workout is better that one that ass that doesn't move. As much as I prefer High-Intensity workouts, Low-Intensity training certainly have their place in any exercise program too. You don't switch simply because something is in vogue.
But why can't an average exerciser do HIIT using the PIT way? Here are the main reasons:
It Is too taxing on the Central Nervous System (CNS)
Any form of high-intensity exercise, whether it’s HIIT cardio training or weight lifting exercise, is going to work your CNS hard. An average trainee simply do not have the capacity to withstand such hard work and can cause the system to take a hit. Prolonged or frequent training with HIIT can severely hurt their recovery, leading to overtraining, become sick and suffer from fatigue syndrome.
It requires the availability of Carbohydrates (ie.Sugar) in your system
You can't really do very intense training if you’re on a low-carb diet. HIIT is technically an exercise that alternates between aerobic and anaerobic modes, meaning that the body needs fuel in the form of glucose to get through it. If you are taking in a limited amount of carbohydrates, there simply won’t be enough sugar to fuel your workout. Training vey intensely in such mode, will leave you feeling vey queasy, not to mention, inability to achieve what you had intended to do.
It is extremely intense
It is what it is - high intensity, it means hard work. It is not everybody's cup of tea. Not everyone craves for high intensity stuff. Apparently I adore it (you can even nickname me as Mr Intensity), but even so many a days I prefer to stay away from pushing myself to limits..
There are many exercisers who just want to take an easy approach toward exercise and it is perfectly alright. I would still be delighted to see people strolling in the park anytime then to see them remaining sedentary. Exercise is already quite an intense activity for beginners. Recently I have a client who left her ex trainer and come to me for training, simply because the former had shouted in her face that she wasn't pushing herself hard enough. Trying to mimic Navy Seals training maybe.
Yes I promote high intensity workouts but I let my clients dictate where their comfortable level of high intensity is at (i.e. their personal hard but manageable zone), while I ensure that the level is valuable enough physiologically. Hard work, after all, is quite subjective. I can't tell you its easy, when you feel it's too tough. How I push my clients through hard session is by using certain psychological motivation methods like giving hints, use of body language and wise choice of words. No yelling is necessary. The end result is that they can often push themselves beyond the level that they thought they couldn't.
The bottomline is: if you are a hardcore well-trained athlete and can handle 'balls to the wall' type of training, go ahead and do HIIT the PIT way. If you are somewhat just seeking for general health, weight loss and have a fun time working out, do the FIT version.
Here is a sample beginner HIIT done in FIT mode:
Walking x 5 mins (Warming up, be able to talk comfortably),
Jogging (or brisk walking if you find jogging too intense) x 1 min (you should be breathing hard but not panting) followed by
Walking x 2 mins (same as warming up pace)
Repeat 3 to 5x
Walking x 3 mins (Cool down, back to comfortable pace)
American College of Sports Medicine (1998). ACSM’s Resource Manual for Guidelines for Exercise Testing and Prescription, 3rd Ed. Baltimore, MD: Williams & Wilkins.
American College of Sports Medicine (2000). ACSM’s Guidelines for Exercise Testing and Prescription, 6th Ed. Baltimore, MD: Williams & Wilkins.
American Council On Exercise (1996). Lifestyle & Weight Management Consultant Manual. American Council On Exercise. San Diego.
Ballor DL, Katch VL, Becque MD, and Marks (1988). Resistance Training During Caloric Restriction Enhances Lean Bodyweight Maintenance. Journal of Clinical Nutrition, 47, 19-25.
Bandini LG, Schoeller DA, and Dietz WH (1990). Energy Expenditure in Obese and Nonobese Adolescents. Pediatric Research, 27, 198-203.
Blair SN and Connelly JC (1996). How Much Physical Activity Should We Do? The Case for Moderate Amounts and Intensities of Physical Activity. Research Quarterly for Exercise & Sport. 67, 193-205.
Blair SN. Wei M, Kampert JB, Barlow CE, Nichaman MZ, Gibbons LW, Paffenbarger RS Jr (1999). Relationship between Low Cardiorespiratory Fitness and Mortality in Normal-Weight, Overweight, and Obese Men. Journal of the American Medical Association, 282, 1547-1553.
Blundell JE and King NA (1999). Physical Activity and Regulation of Food Intake: Current Evidence. Medicine and Science in Sports and Exercise, 31 (11 Suppl), 573-583.
Bouchard C (2000). Physical Activity and Obesity. Champaign: Human Kinetics.
Bray GA. (1996) Health Hazards of Obesity. Endocrinology and Metabolism Clinics of North America, 25, 907-919.
Bryner RW, Toffle RC, Ullrich IH, and Yeater RA (1997). The Effects of Exercise Intensity on Body Composition, Weight Loss, and Dietary Composition in Women. Journal of the American College of Nutrition, 16, 68-73.
Bryner RW, Ullrich IH, Sauers J, Donley D, Hornsby G, Kolar M, and Yeater R (1999). Effects of Resistance vs Aerobic Training Combined with an 800 Calorie Liquid Diet on Lean Body Mass and Resting Metabolic Rate. Journal of the American College of Nutrition, 18, 115-121.
Burgess NS (1991). Effect of a Very-Low-Calorie Diet on Body Composition and Resting Metabolic Rate in Obese Men and Women. Journal of American Diet Association, 91, 430-434.
Cotton RT (1997). Personal Trainer Manual: The Resource for Fitness Professionals. American Council on Exercise. San Diego.
DeBusk RF, Stenestrand U, Sheehan M, and Haskell WL (1990). Training Effects of Long versus Short Bouts of Exercise in Healthy Subjects. American Journal of Cardiology, 65, 1010-1013.
Deurenberg-Yap M, Schmidt G, van Staveren WA and Deurenberg P (2000). The Paradox of Low Body Mass Index and High Body Fat Percentage among Chinese, Malays and Indians in Singapore. International Journal of Obesity and Related Metabolic Disorders, 24, 1011-1017.
Dishman RK (1988). Exercise Adherence: Its Impact on Public Health. Champaign: Human Kinetics.
Donnelly JE, Jacobsen DJ, Heelan KS, Seip R, and Smith S (2000). The Effects of 18 Months of Intermittent vs. Continuous Exercise on Aerobic Capacity, Body Weight and Composition, and Metabolic Fitness in Previously Sedentary, Moderately Obese Females. International Journal of Obesity and Related Metabolic Disorders, 24, 566-572.
Eckel RH (1997). Obesity and heart disease. Circulation, 96, 3248-3250.
Esparza J, Fox C, Harper IT, Bennett P, Schulz LO, Valencia ME and Ravussin E (2000). Daily Energy Expenditure in Mexican and USA Pima Indians: Low Physical Activity as a Possible Cause of Obesity. International Journal of Obesity and Related Metabolic Disorders, 24, 55-59.
Ferraro R, Boyce VL, Swinburn B, De Gregorio M, and Ravussin E (1991). Energy Cost of Physical Activity on a Metabolic Ward in Relationship to Obesity. American Journal of Clinical Nutrition, 53, 1368–1371.
Golding LA, Meyers CR, and Sinning WE (1986). The Y's way to Physical Fitness (3rd Edition). Champaign: Human Kinetics.
Grediagin A, Cody M, Rupp J, Benardot D, and Shern R (1995). Exercise Intensity does not Effect Body Composition change in Untrained, Moderately Overfat Women. Journal of American Diet Association, 95, 661-665
Griffin SE, Robergs RA, and Heywards VH (1997). Assessment of Exercise Blood Pressure. A Review. Medicine and Science in Sports and Exercise, 29, 149-159.
Grilo GM (1995). The Role of Physical Activity in Weight Loss and Weight Loss Management. Medicine, Exercise, Nutrition and Health, 4, 60-76.
Hall F (1999). Which is Better for Weight Loss - High Intensity or Low Intensity Exercise? Journal of New Zealand Dietetic Association, 53, 62-65.
Heyward V (1998). Advanced Fitness Assessment and Exercise Prescription (3rd Edition). Champaign: Human Kinetics.
Hunter GR, Weinsier RL, Bamman MM, and Larson DE (1998). A Role for High Intensity Exercise on Energy Balance and Weight control. International Journal of Obesity and Related Metabolic Disorders, 22, 489-493.
Hurley BF, Hagberg, Goldberg AP, Seals DR, Ehsani AA, Brennan RE, and Holloszy JO (1988). Resistance Training can reduce Coronary Risk Factor without altering VO2max or Percent Body Fat. Medicine and Sceince in Sports and Exercise, 20, 150-154.
Lee IM, Hsieh CC, and Paffenbarger RS Jr. (1995). Exercise Intensity and Longevity in Men. The Harvard Alumni Health Study. Journal of the American Medical Association, 273, 1179-1184.
McArdle W D, Katch F I, and Katch V L. (1996). Exercise Physiology: Energy, nutrition, and human performance. Maryland: William & Wikins.
Nieman DC (1995). Fitness and Sports Medicine. Mountain View, CA: Mayfield Publishing.
Owens S, Gutin B, Allison J, Riggs S, Ferguson M, Litaker M, and Thompson W (1990). Effect of Physical Training on Total and Visceral Fat in Obese Children. Medicine and Science in Sports and Exercise, 31, 143-148.
Pacy PJ, Webster J, and Garrow JS (1986). Exercise and Obesity. Sports Medicine, 3, 89-113.
Park RJ (1992). Human Energy Expenditure From Australopithecus afarenis to the 4-minute Mile: Exemplars and Case Studies. Exercise and Sport Sciences Reviews, 20, 185-220.
Pate RR, Pratt M, Blair SN, Haskell WL, Macera CA, Bouchard C, Buchner D, Ettinger W, Heath GW, King AC, Kriska A, Leon AS, Marcus BH, Morris J, Paffenbarger RS, Patrick K, Pollock ML, Rippe JM, Sallis J, and Wilmore JH (1995). Physical Activity and Public Health: A Recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. Journal of the American Medical Association, 273, 402-407.
Poehlman ET, Melby CL, Badylak SF, and Calles J. (1989). Aerobic Fitness and Resting Energy Expenditure in Young Adult Males. Metabolism, 38, 85-90.
Prentice AM and Jebb SA (1995). Obesity in Britain: Gluttony or Sloth. British Medical Journal, 311, 437–439.
Prentice AM, Black AE, and Coward WA (1986). High Levels of Energy Expenditure in Obese Women. British Medical Journal, 292, 983-987.
Snyder KA, Donnelly JE, Jabobsen DJ, Hertner G, and Jakicic JM (1997). The Effects of Long-term, Moderate Intensity, Intermittent Exercise on Aerobic Capacity, Body Composition, Blood Lipids, Insulin and Glucose in Overweight Females. International Journal of Obesity and Related Metabolic Disorders, 21, 1180-1189.
Spirito P, Pelliccia A, Proschan MA, Granata M, Spataro A, Bellone P, Caselli G, Biffi A, Vecchio C, and Maron BJ (1994). Morphology of the "athlete's heart" Assessed by Echocardiography in 947 Elite Athletes representing 27 Sports. American Journal of Cardiology, 74, 802-806
Tremblay A, Despres J-P, and Bouchard C (1985). The Effects of Exercise-Training on Energy Balance and Adipose Tissue Morphology and Metabolism. Sports Medicine, 2, 223-233.
Tremblay A, Simoneau JA, and Blouchard C (1994). Impact of Exercise Intensity on Body Fatness and Skeletal Muscle Metabolism. Metabolism: Clinical and Experimental, 43, 814-818.
Treuth MS, Hunter GR, and Williams M (1996). Effects of exercise intensity on 24-h energy expenditure and substrate oxidation. Medicine and Exercise Science in Sports and Exercise, 28,1138-1143.
Walberg J (1989). Aerobic Exercise and Resistance Weight-Training During Weight Reduction - Implications for Obese Persons and Athletes. Sports Medicine, 47, 343-356.
Weyer C, Linkeschowa R, Heise T, Giesen T, and Spraul M (1998). Implications of the traditional and the new ACSM Physical Activity Recommendations on weight reduction in dietary treated obese subjects. International Journal of Obesity and Related Metabolic Disorders, 22, 1071-1078.
Wolf A and Colditz G (1998). Current Estimates of the Economic Cost of Obesity in the United States. Obesity Research, 6, 97-106.
Hardcastle SJ, Ray H, Beale L, Hagger MS. Why sprint interval training is inappropriate for a largely sedentary population. Front Psychol. 2014;5. ARTN 1505 pmid:WOS:000348147800001.
Talanian JL, Galloway SDR, Heigenhauser GJF, Bonen A, Spriet LL. Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women. J Appl Physiol. 2007;102(4):1439–47. pmid:WOS:000248410500025.
Biddle SJH, Batterham AM. High-intensity interval exercise training for public health: a big HIT or shall we HIT it on the head? Int J Behav Nutr Phy. 2015;12.
Gist NH, Fedewa MV, Dishman RK, Cureton KJ. Sprint interval training effects on aerobic capacity: a systematic review and meta-analysis. Sports Med. 2014;44(2):269–79. pmid:24129784.
Bartlett JD, Close GL, MacLaren DPM, Gregson W, Drust B, Morton JP. High-intensity interval running is perceived to be more enjoyable than moderate-intensity continuous exercise: Implications for exercise adherence. J Sport Sci. 2011;29(6):547–53.
Foster C, Farland CV, Guidotti F, Harbin M, Roberts B, Schuette J, et al. The Effects of High Intensity Interval Training vs Steady State Training on Aerobic and Anaerobic Capacity. J Sports Sci Med. 2015;14(4):747–55
Helgerud J, Hoydal K, Wang E, Karlsen T, Berg P, Bjerkaas M, et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sport Exer. 2007;39(4):665–71
Kessler HS, Sisson SB, Short KR. The potential for high-intensity interval training to reduce cardiometabolic disease risk. Sports Med. 2012;42(6):489–509. pmid:22587821.
Almenning I, Rieber-Mohn A, Lundgren KM, Shetelig Lovvik T, Garnaes KK, Moholdt T. Effects of High Intensity Interval Training and Strength Training on Metabolic, Cardiovascular and Hormonal Outcomes in Women with Polycystic Ovary Syndrome: A Pilot Study. Plos One. 2015;10(9):e0138793.
Godfrey RJ, Madgwick Z, Whyte GP (2003) The exercise-induced growth hormone response in athletes. Sports Med 33: 599-613.
Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, Yamamoto K. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Med Sci Sports Exerc. 1996 Oct;28(10):1327-30.
Emberts, T., Porcari, J., Dobers-tein, S., Steffen, J., & Foster, C. (2013). Exercise Intensity and Energy Expenditure of a Tabata Workout. Journal of Sports Science & Medicine, 12(3), 612–613.
Tabata I, Irisawa K, Kouzaki M, Nishimura K, Ogita F, Miyachi M. Metabolic profile of high intensity intermittent exercises. Med Sci Sports Exerc. 1997 Mar;29(3):390-5.
Schantz P. Along paths converging to Bengt Saltin's early contributions in exercise physiology. Scand J Med Sci Sports. 2015 Dec;25 Suppl 4:7-15. doi: 10.1111/sms.12594. Review. PubMed