High Intensity Exercise Training, is it worth doing less to get more?


By Evan L. Lipkis MD



Is exercise really worthwhile?




You bet it is. According to a meta-analysis, BMJ 2016; 354 doi: https://doi.org/10.1136/bmj.i3857 (Published 09 August 2016), regular exercise helps to decrease the following 5 diseases: breast cancer, colon cancer, diabetes, coronary heart disease and ischemic strokes. Not bad huh? And the more time you devote to exercise, the greater the benefits. 


Of course, I didn’t go over other the other benefits of exercise which can include stress reduction, improved mood, weight maintenance/loss, stronger bones, cholesterol/sugar reduction and dementia reduction.


The WHO or World Health Organization recommends 150 minutes of moderate exercise per week but unfortunately only a 1/3 of adults or less meet this threshold. WHO also recommends major muscle group strengthening two days a week. Everyone needs to adjust these levels according to their health status and in conjunction with their health care provider. This is especially true for the elderly.



What is high intensity interval training?


High intensity interval training (HIIT) is a way of deriving the full benefits of exercise but in less time. An example would be to cycle at 90% of your maximal heart rate for 1 minute and then rest for 2 minutes and repeat 5 times. Your maximum heart rate is approximately 220 minus your age. So you end up exercising less than regular exercise but seem to get the same benefits. This is the appeal of HIIT. With regular exercise, one usually aims to go at 70% of the maximum heart rate for 30-45 minutes. 


You can also make the ratio higher or lower depending upon your level of fitness. So you could exercise for 2 min. and rest 1 min. or exercise 2 min. and rest for 3 minutes. The choice is yours regarding your initial level and how you build up. You can also do different types of activities such as running, jumping, cycling or even push ups. 



Isn’t it dangerous to exhaust yourself by going all out?


Generally speaking HIIT is safe to do even in lower risk heart patients Int J Cardiol. 2017 Jun 17. [Epub ahead of print]. One can always increase the rest interval after going at near maximal heart rates. For any exercise program, obtain approval by your physician. 


One potential danger of exercise is rhabdomyolysis. Rarely with heavy exercise the muscles can start to break down yielding toxic substances that can damage the kidneys. Symptoms and signs can include brownish urine, persistent achy muscles, muscle weakness, elevated CPK (a muscle enzyme blood test) and elevated kidney function. Fortunately, this is an uncommon condition. Admission to the hospital is usually indicated so that IV fluids can be administered in order to wash out the toxins.


Dehydration with higher temperatures can also occur so be sure to have a water bottle with you. Common symptoms include dry mouth and dizziness (feeling like you might black out) especially upon standing. Dehydration is quite common and readily  reversible with fluids. Many serious athletes require added salt since sweating is really just salty fluid. So excessive sweat loss and replacement with only water can result in a low sodium which can cause harm to the central nervous system such as seizures. Using sport drinks with added salt is appropriate.

Exercise induced cramps can be quite painful and may be helped by hydration and interestingly, spicy beverages. See my article entitled Muscle Cramps, what to do.


Finally heat stroke is a very serious ailment that occurs during exercise especially over age 50. Characteristically, sweating stops so heat from the body cannot be dissipated. The core body temperature can rise to 104 degrees or higher and the skin is often hot and dry. Additionally, cognitive impairment can occur as well. This is a medical emergency since the high core temperature can cause internal organ damage including the brain, so call 911. A cool water bath plus fluids can be very helpful. Fanning and pouring water on the victim’s clothing may also work while waiting for the ambulance. Hot and humid days are risk factors for heat stroke. Also higher humidity can impair sweating.


What about weight loss?


Actually, according to the June 11th 2019 issue of JAMA, HIIT resulted in more fat loss in 25 minutes than regular exercise extended for 41 minutes. Dr. Paulo Gentil, one of the authors, states that HIIT is a more efficient way to exercise. And if you have a bad knee, you can cycle or swim. 


In other words, there always seems to be an exercise that you can do with high intensity. Obviously you should talk to your physician or healthcare provider regarding any type of exercise.



Do you think tennis is a form of HIIT?


Actually tennis is a form of HIIT because you are resting between points and going full blast during the point. Racket sports like tennis, badminton, and squash offer the greatest boost to your health. In fact, in a 2012 study, racquet sports provided a 47% reduction in death from all causes and a 56% reduction in cardiovascular death. Swimming and aerobics also reduced death by about 27%. So essentially racquet sports can be a form of HIIT and the benefits seem to be greater than other aerobic sports. Of course, the take home message is still to do the exercise you enjoy since you are likely to continue doing it.


Are there any studies comparing HIIT to moderate exercise? 






 Ok, your wish is my command! 



  • Resting energy expenditure or REE was actually higher post HIIT vs. moderate aerobic exercise. So this type of exercise serves to blow off calories even after you are done doing HIIT. Any exercise can increase   calorie consumption while resting but HIIT seems to do it more. PMID: 27747847 DOI: 10.1186/s40798-015-0010-3


  • HIIT was superior to moderate exercise regarding vascular function. If you have good vascular function, then you are less likely to develop cholesterol plaque in your arteries. K. G. Jebsen Center for Exercise in Medicine at Department of Circulation and Medical ImagingNorwegian University of Science andTechnology(NTNU)TrondheimNorway,Systematic ReviewFirst Online: 15 March 2015


  • HIIT was better than regular moderate exercise with regards to reduction in % body fat in overweight females. Both types of exercise were equal in helping subjects to reduce both BMI and weight. The weight loss was mild. Faculty of Sports Science and RecreationUniversiti Teknologi MARANegeri SembilanMalaysia, Conference paperFirst Online: 29 July 2014


  • VO2 max or maximum oxygen uptake is greater for the HIIT group vs. the moderate exercise group. Interestingly, the HIIT group did 4-7 intervals of maximum cycling on a Wingate bike (30 sec followed by 4.5 minutes of rest). So, in one session, the HIIT group did 2-3.5 min. of exercise vs. 40-60 min. of exercise in the moderate cycling group. That means the HIIT group exercised about 10 minutes a week or less for 3 sessions while the moderate exercise group exercised 2-3 hours per week with the same number of sessions. Wow, what an efficient use of your time!


Dr.’s. Rx: Most people are sedentary, so exercise is a very valuable commodity. You won’t get much weight loss from it but the incidence of many diseases plummets. Remember to make exercise fun if you can. Owning a dog allows for 20% more exercise than if you don’t own one. HIIT can provide a number of benefits equal to or greater than regular, moderate exercise in less than 1/3 the time. The benefits can even be realized in low risk cardiac patients. While there are many studies to support HIIT, the number of participants is small. Talk to your doc about this interesting way of exercising. 

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