Repair of the system

Currently, the most commonly used criterion for determining whether the body mass is normal, or too small, or too big, is the body mass index (BMI). The formula of this index is such: body mass in kilograms (m) over the height in meters squared (h²). 

BMI =  m / h² 

For instance, if the weight is 80 kg, and height is 180 cm (1.8 m),
BMI =  80 / 1.8² = 80/3.24 ≈ 24.7
And for the weight of 61 kg and height of 172 cm,
BMI =  61 / 1.72² = 61 / 2.9584 ≈ 20.6

For non-SI units (pounds and inches), the result of the division needs to be multiplied by 703 (this number is just a correcting coefficient).
weight (lb) / [height (in)]2 × 703 

It is thought that BMI in the range from 18.5 to 24.9 corresponds to the normal body mass, from 25.0 to 29.9 means overweight, and over 30 means obesity. And obesity is divided into three stages: the first (30-34.9), the second (35-39.9), and the third that starts from BMI 40 and does not have the upper limit. If height is 180 cm (70.87 in.) BMI  40 corresponds to the weight of almost 130 kg (286.6 lb.). These values are the same for adult women and men (or humans of any other genders) and does not change with age.

Of course, this index does not take into consideration development of muscles and peculiarities of the skeleton. Measuring these parameters and introducing them into the index would be rather complicated. Instead, a compromise between complexity of measurement and limited accuracy was chosen. To compensate for the limited accuracy, a rather wide range for normal body mass was set. For instance, at the height of 180 cm  (70.87") , the BMI is though to be normal in the range of weight from 59.9 kg (132 lb.) to 80.7 kg (177.9 lb.). The difference is rather substantial – the upper margin is by over 30% above the lower, and the lower is by over 25% below the upper. For somebody of this height, 60 kg is too little, and for somebody else, 80 kg is too much, but their BMI is formally in the normal range.

Our organism knows its own normal body mass and can maintain it in the range  ±2 kg, or even more precisely, ±1,2 kg (±2,7 lb.), if our system of automatic regulation is not broken. And this normal body mass is very individual. There are people, for whom the body mass, which, according to the standards, corresponds to overweight or even a light form of obesity, is normal. There is a whole ethnos, in which all people look like they are somewhat obese, according to our standards. But, in fact, these people are absolutely healthy. 

And vice versa, there are people whose body mass is within the norm, and they even look lean, because they do not have much subcutaneous fat, but they have a lot of visceral fat and a lot of fat tissue in the liver, which can be seen via the magnetic resonance imaging (MRI). And they have many of the health disorders related to excess body mass, including type two diabetes.

If your BMI exceeds 25.0, can it be that this is your normal body mass? It can, if you do not have any issues with health, your muscles are well-developed and you can easily spend 24 hours not eating at all. But if you cannot fall asleep unless you stuff yourself with food to the limit and, perhaps, wake up at night to eat, and then have breakfast early in the morning, it is very likely that your system of automatic regulation is broken, and your body mass may exceed your individual norm, even if you BMI is normal.

Since the normal body mass is very individual, taking weight loss as a goal does not make much sense. Besides, most people who try to achieve it, fail, because conscious limitation of "calories" means constant starvation, and it is difficult, it is suffering. Not many can withstand voluntary suffering for long.

And some (especially young women and girls) sometimes achieve this goal "goo well" – they bring themselves to anorexia, of which some of them even die. Anorexia is rather a psychological problem than a physiological one. Often, girls with anorexia, while already looking like skeletons in skin, still believe that they are too fat and want to lose weight. 

So, what goal is strategically correct? Repair of the system of automatic regulation of the balance between consumption, accumulation and expenditure of energy, if there are signs that this system is broken. Or preservation of this system, if it is not broken. This goal is strategically correct.

There are calories, and there are calories, and they are different.

Sure, laws of physics and, in particular, thermodynamics, do apply. If one consumes more calories than spends, the energy will be accumulated, and if expenditure exceeds consumption, the energy stocks will shrink. 

It is rather easy to consume more than to spend by keeping to the rules of breaking the system. But forcing oneself to spend more than to consume for a long time is almost impossible, and gradually either expenditure will reduce, or consumption will increase. 

The problem with accumulation of calories in the organism with the broken system is that some calories (in the form of glucose) can be spent, while others (in the form of fats) are not allowed to be spent, and so they accumulate. Moreover, an excess of calories in glucose can be accumulated in glycogen, but its stocks are limited. Therefore, glucose that cannot be stored in glycogen, is converted into fats, spending of which is blocked. This is related to constantly or almost constantly high level of insulin in the broken system – this is the high level of insulin that blocks expenditure of fats. And in the system that is not broken, any calories can be spent (perhaps, not all the time, but most of the time), and this is what is done.

Counting of calories, which some people do when they try to lose weight, looks rather pointless. A considerable part of proteins is not used as calories. The accuracy of the data on calories in food is not high. Not all calories that we eat are absorbed, and to accurately establish, which part is absorbed, and which is not, is very difficult and expensive. Expenditure of calories is so difficult to measure that it is better not to even try (though, there are approximal experimental estimations). If the system we speak about is not broken and works normally, it automatically maintains a balance of consumption and expenditure, regardless of whether you count calories or not. 

If, despite warnings at the beginning of this page, you will consider this text as a direct recommendation, make sure to read the section "Exceptional cases" (further on this page) before blindly following what is not intended to be a recommendation and is just an information for thoughts. 

Very IMPORTANT! What is written here is certainly not about type one diabetes, because that is a completely different case related to absence of insulin in blood, and not to its excess.

What breaks the system? Too frequent eating of food that contains a lot of glucose (carbohydrates). Therefore, reverse actions will cause a reverse effect. Namely, an increase of intervals between taking meals and decrease of glucose (carbohydrates) in the food (by replacing carbohydrates with saturated fats). 

On the increase of the intervals. In fact, it is enough that just one interval a day (in 24 hours) should be sufficiently long for insulin, elevated after taking the previous meal, to "push" glucose into all cells that can accept it and to get lower.  As soon as it (insulin) lowers under the threshold of spending fats, the organism will start spending fats, even if not all accumulated glucose has already been burnt. 

The simplest and completely natural such an interval can be between the last meal the day before and the first meal on the current day. It must be at least 10 to 12 hours. No snacks late in the evening, and certainly not when you wake up in the middle of the night. Or, if, because of your work schedule or life stile you have to eat at night, then you should not have breakfast early in the morning. 

But if the system is already broken, this may be not enough. It is better that the interval between the last meal yesterday and the first meal today should be 16 to 18 годин. Sometimes, it is recommended to skip supper. But this is not important. It is OK to eat at night and do not eat during the daytime. It is not the time when you eat that important, but the duration of the longest interval. For many people, it is easier to skip breakfast than to skip supper. Those who tried to skip breakfast and managed to do this (yes, it is somewhat difficult for the first one to three days), say that they work easier, they feel livelier and less tired. 

An interval between meals of 16 to 18 hours – is it possible at all? Yes. Imagine our distant ancestor. Here he wakes up in the morning in his cave and goes to the fridge. Opens it, takes a bottle of yogurt, cuts a thick slice of sausage and... Wait, he did not have a fridge in his cave. And all food he hunted and gathered yesterday was eaten yesterday. So, he woke up and went hunting and gathering something edible. Surely, everything edible near his cave had been found and eaten long ago, so he had to walk and run around a lot before could get enough food for breakfast. Therefore, his breakfast was closer to the noon. And his kids had breakfast when he managed to hunt something rather than when they woke up. Not always hunting was successful. In such cases, eating would have to be postponed for longer, sometimes, for several consecutive days. The fact that we live now is an evidence that our ancestors did not die out with this regimen of eating. Perhaps, we will not die either, if we follow this pattern of eating. 

There are people who eat only once a day (they even have a special term for this: OMAD – one meal a day). They allocate an hour or two in the middle of the day or in the evening for having meal and eat until they are satiated. And then they do not eat until this time next day. In India, there is a whole ethnos, in which, eating once a day in the evening is a centuries-long tradition. If this schedule of eating were harmful, they all would have died out long ago. But they live, and there are almost no cases of obesity or high blood pressure among them. And cardio-vascular diseases to not affect them until a very senile age. And there are no cases of type two diabetes at all. 

On reduction of glucose. We get glucose almost exclusively from plant food, which contain a lot of carbohydrates. But glucose is a "fuel" for mitochondria. If we limit intake of carbohydrates, we will starve, won't we? Not necessarily. Glucose can be replaced with fats, especially, saturated ones. Besides, we need twice as little fats as glucose because fats have around 9 kcal/g,  while glucose only 4. Besides, out of fats, our liver produces ketone bodies, which are a better fuel than glucose or fatty acids. For this, it is necessary that the insulin level should be below the one that blocks expenditure of fats.

It is simple to replace carbs with fats. Dairy products like yogurt (not sweet), kefir, curd – only not low-fat or fat-free, but with normal content of fats; butter, ghee. Pork fat (a traditional food for Ukrainians). Fatty fish, meat, eggs. All these are also sources of proteins. Vegetable unsaturated fats in moderate quantities, especially olive or flax seed extra virgin oils. We will discuss fats separately. 

In the process of repairing the system, it may be necessary to tolerate a certain discomfort before the largest interval between meals is brought to 16-18 hours. Some people can di this at once and will feel discomfort for 1 or 2 days only. Others may have to do this gradually and "suffer" for a whole week. But during the time allocated for eating (6 to 8 hours a day), we may eat as much as we can stuff into ourselves, until we feel satiety; and then we should not eat at all until the next such period. As much as we can, but not anything we can. Smaller amounts of carbs, larger amounts of saturated fats, enough unsaturated fats (especially, omega-3), enough proteins and, of course, vitamins, minerals and things like these. 

And, of course, physical exercise or physical activity in general. Yes, they are vitally necessary, but, on their own, they do not have a strong influence on the body mass and repair of the system. Perhaps, they do, if you devote to them a lot of time and effort. For instance, to burn twice as much energy as we spend when stay in bed all day, we need to walk rather quickly for 10 or more hours a day. But it will be easy to gain twice as much energy, especially if the system is broken. Tiredness is not a measure of physical activity. One can get tired after sitting all day at a desk. But when both measures described above are applied, physical exercise can improve the result, though, not through just burning energy. In any case, physical activity is essential because life is motion, and motion is life. 

Possible complications. Breaking the system takes time, typically, 10 to 20 years. If one tries very hard, this can be done faster, but still several years will be necessary. The repair of the system also takes time. Not as much of it as breaking the system, but from several months to a year, or even two, may be needed to get rid of the insulin resistance and restore normal level of insulin with not very large swings and with a substantially long period when its level is below the threshold that blocks spending fats. 

During the repair, there can be complications and unpleasantness, because, while insulin is still high, cells cannot obtain a sufficient amount of fatty acids. Ketone bodies can be accepted by cells regardless of the insulin level, but they are produced by the liver out of fatty acids, for which it needs to switch over to their production, and it has not been doing this for years. Also, mitochondria, for a very long time, got used to burn glucose almost exclusively. Therefore, there will be a period of adaptation of the organism to the long-forgotten normal conditions, and this may be unpleasant. A shortage of energy in the cells may periodically occur when there is not much glucose already, and not much of fatty acids and ketones yet, and mitochondria have not restored their ability to burn them yet.  This may cause periodical weakness, dizziness, speeded-up heartrate, especially if physical activity is also increased, which earlier was too low. Eventually, these unpleasant feelings will go away. But there can be other causes of such symptoms, therefore, if they do not disappear when the physical activity is lowered, it is reasonable to consult with a doctor. But you need to be ready that the doctor will recommend to abandon efforts on repairing the broken system and will prescribe expensive pills, which may be really effective, but they act on symptoms, rather than on the causes of breaking the system.

ATTENTION! For some people, the described approach to the repair of the system may be dangerous. This is not because this approach is wrong, but because organisms of some people have disorders, which developed independently from those that broke the system. 

Here are just two cases (there are videos about both), but there can be many more, and they may have different origin. 

Case one. Once a video was posted on YouTube: "The keto diet may kill you".  That video presented a story of a woman who tried to use the so-called keto diet for losing body weight. We will discuss diets later, and for now it is enough to know that this diet is oriented at consumption of very small amounts of carbs and consumption of fats as the main sources of energy, and its goal is to make the organism switch to production of ketone bodies out of fats and expenditure of these ketone bodies as the main source of energy.

So, after a short time after using this diet, the woman was rushed to a hospital by an ambulance because she felt very bad. She was almost in coma. Among other urgent examinations, doctors measured her blood glucose, and its level appeared very low. She was administered an intravenous injection of glucose. This was enough to improve her condition, and she was released to go home.

However, neither the woman, no the doctors, related this accident to the keto diet. And the woman had not even told doctors that she had begun to use it. Therefore, the woman continued, and was rushed to the hospital again, and again with a catastrophically low blood glucose level. She was resuscitated in the same way and released. 

Only when the woman got to the hospital for the third time, one of the doctors decided to carry out some more examinations, including the test of the level of insulin in blood. And this test showed that the insulin level in this woman was way too high, even higher than it can ever be with the healthy pancreas. Further investigation showed that the woman had a rare form of pancreatic cancer. Specifically, the cells that produce insulin (and only they) turned into cancer cells. At that, as all cancer cells do, they freed themselves from the supervision of the organism and began to reproduce themselves uncontrollably. But they preserved the ability to produce insulin, and produced it at their maximum capacity.

This is what happened to the woman. When she consumed a lot of carbs, they were converted into glucose, which was pushed into cells of different organs, including muscles, the brain and the liver. Partially it was used as energy for charging ATP, and partially was converted into fats and, which were accumulated. When the woman started using the keto diet, the influx of glucose into blood sharply reduced, but the organism could not use fats as a source of energy because of the too high insulin level. This is why the blood glucose dropped, and the woman felt very bad. 

Thus, this video should have been titled: "Cancer can kill you". And this is true. The cause of the problem was not the keto diet, but the pancreatic cancer. Hadn't the woman been so persuasive in using the keto diet, who knows for how long her oncological disease would have remained undetected. After that, the woman was administered a cancer treatment. But this is a different story.

Case two. A little boy began to gain weight very quickly. When he was nine, his body weight exceeded 80 kg (176 lbs.).  The parents raised alarm. The doctor whom they had contacted prescribed a low-calorie diet. This did not help. Even when the calories in the boy's food were reduced to 500 kilocalories per day, by 2.5-3 times less than a child of this age normally spends, considering naturally high physical activity of children, the boy continued to gain weight. But he preferred not to move much, quickly got tired and slept a lot. 

Parents addressed another doctor, who understood how the system of automatic regulation of consumption, expenditure and accumulation of energy works. This was somewhere between the years 2000 and 2010, when there were very few such doctors. 

So, the first prescription of this doctor was the blood insulin test. Indeed, the insulin level appeared to be too high, close to the upper limit of the capability of the pancreas to produce it. No, this child did not have pancreatic cancer; and, in general, everything was all right with his pancreas. But, about a year earlier, the boy had a tumor removed from his brain. And it was after this surgery that he began to gain weight. 

It appeared that that tumor had been in the part of the brain responsible for regulating the level of insulin. Because of the tumor, or as a result of the surgery, this part of the brain began to work improperly, issuing signals for production of the excess about of insulin, even there was no need in it. Because of this, the boy accumulated most of the food he ate in the form of fats. 

The doctor prescribed medications that lowered production of insulin. The boy began to lower his body weight to the norm and returned to normal physical activity and normal diet.

Of course, these two cased do not cover all possible situations, when something may go wrong. But they also show that the ways of breaking the system and repairing it are not entirely groundless. And also, they signal that one should be very attentive to oneself, especially at abrupt changes of the manner of eating. 

It is believed that 8 out of 10 people can repair their system of regulation in this way (a rather cautious estimation). But this means that two out of ten may have additional health problems, with which this approach either will not work, or may even cause harm. So, be attentive to yourselves, if you decide to try. 

Usually, keeping the largest interval between meals over 12 hours is called intermittent fasting. This may be scary for those who want to repair their metabolism, because they expect that they may starve. In fact, this is not starvation. The feeling of hunger may indeed appear and be rather strong in the first several days (often, just one day). And later, it does not appear, or appears only sometimes, is rather slight, and passes quickly, unless you urgently stuff some food into you. By the way, there are different religious traditions of fasting, and not all of them require complete refraining from all food, but only from some kinds of food. Here, we speak about "strict fasting", or "only water fasting", when we do not eat anything for 18 hours, and only drink water (or tea/coffee without sugar), than we eat as much as we want for 6 hours, and then fast strictly for another 18 hours, and so on. 

Besides a substantial decrease of the glucose level and subsequent decrease of the insulin level that makes accumulated fats available as fuel (including active production of ketone bodies), by the end of the period of such a strict fasting, other useful processes occur. 

After the twelfth hour of  refraining from eating, the so-called autophagy activates – the organism begins to seek sources of amino acids inside itself. The nearest such source is damaged proteins, which are disassembled into amino acids, which are then used for assembling new proteins to replace damaged ones.

Also after 12 hours, production of the human growth hormone increased. In adults, this hormone does not stimulate growth of the body (like increase of height), but it speeds up replacement of worn-out cells with new ones, and also it promotes the increase of the number of mitochondria in cells.

These three processes – transition to fat burning, autophagy and production of the human growth hormone – become twice as strong, if the fasting period is increased to 16-18 hours. And after the 40th hour, then are twice as strong as they are after 18 hours. If fasting is continued, these processes continue to strengthen, but not as quickly as before, and, somewhere after the seventh day, they reach their maximum and do not get stronger anymore.

It is often recommended, in addition to regular fasting periods of 16 to 18 hours (or 22 to 23 hours for those who have chosen to have one meal a day), to make 40 to 44 hours of fasting once or twice a month, or at least once in two or three months. And also, rarely, once or twice a year, to refrain from food for 3 to 5 days. 

During the intermittent fasting lasting over 40 hours, one should refrain from too intensive physical activity, especially while adaptation of the organism to burning fats has not yet been achieved. One to two hours of moderate physical activity will be enough in this period. If work or life demand permanent physical activity of high intensity, it is better not to practice fasting for over 40 hours. 

These are general recommendations for abstract people, and it is not intended personally for you. If you decide to try, interrupt such fasting immediately, if you feel bad. Normally, during and immediately after such fasting, people feel lightness, a surge of energy and clearness of thoughts, though they may feel light hunger periodically and briefly, for several minutes at a time. 

Important! When fasting for more 24 hours, one should take care on the "balance of electrolytes" (aka salt-and-water balance), that is, about presence of salts in the organism, first of all, salts of sodium, potassium and magnesium.  This can be achieved if, in addition to tea/coffee without sugar and water, to drink mineral water with mineralization 0.4 to 1.0 grams per liter (400 to 1000 mg/l), or add 0.4 to 0.6 grams per liter of sea salt to usual water (the sea salt contains the most essential salts in about the right proportion), or at least common kitchen salt can be used. 

Aldo important! Strict fasting for longer than 4 or 5 days should be done under medical observation, especially for those who have not done this before and do not know how their organism will react to such fasting. 

If, while fasting for just 24 hours or even less, you feel very bad, it is likely that you have some additional serious health problems. In this case, you need to see a doctor immediately.

As already mentioned, the main purpose of physical activity is not burning calories. Yes, some additional calories can be burned, but, to burn any significant number of them, there has to be a lot of physical activity – 8 to 12 hours a day. Of course, one may get a job in a smith's shop as a smith and swing a heavy manual hammer for 12 hours a day, or start training for the national championship; but this does not suit everyone. And this is not necessary, because the normally operating metabolic system automatically maintains the balance between consumption, accumulation and expenditure of energy.

Motion generates a large stream of signals to our brain and stimulates its operation not less stronger than solution of intellectual problems. Our muscles signal about their contraction, joints signal about the angles, by which they are turned, and many more other signals go to our brain. And it reacts to them and produces signals for controlling the muscles and joints. And not only. It is necessary to supply muscles with energy and oxygen, and for that, orders to relevant systems must be issued. And these systems also begin to signal their conditions more actively. And it is also important to maintain mechanical balance of the body (to prevent falling), for which, signals from the vestibular apparatus, eyes, ears and again from the muscles and joints are involved. 

Even when we just stand, about 100 large and small muscles work constantly to maintain our vertical position, and our brain constantly works, processes feedback signals from the muscles, joints, vestibular apparatus and eyes, and issues control signals. 

Maintenance of the muscle mass, elasticity of tendons, ligaments and joints and the strength of bones is a complex and costly task for the organism. Therefore, as soon as the organism realizes that all this is not necessary (because we do not move much), it reduces expenditure of resources on performing this task. And, after a while, our muscles grow smaller, our joints become "rusty", and our bones become brittle. 

And there is the cardio-vascular system. The organism saves expenses on it too, if there is no need to move intensively.

It means that, if we stop moving, completely or almost completely, in a couple of months, it will be very difficult to start moving again. Motion is life. 

Physical activity can be "aerobic" or "anaerobic". Aerobic activity is rather moderate. In it, recharging of ATP molecules is done in mitochondria with the use of oxygen. Approximately, we can expect that physical activity remains completely aerobic up to the heart rate of 100 to 110 beats per minute, and for better physically fit people, this can be up to 125 beats per minute (this is if the "resting" heart rate is 60 to 75 beats per minute). At a higher intensity of the exercise or at an abrupt transition from resting to intensive movement, charging of ATP in mitochondria may be not enough, and then fermentation of glucose without oxygen is added – the activity becomes anaerobic.

Physical exercise should not be too intensive. That is, it should be aerobic most of the time. The simplest and quite sufficient activity for the majority of people is just walking in a not very fast tempo, but not very slow either. About one to two hours of walking a day will provide the required minimum. Morning physical exercise is also a very good habit – 15 to 30 minutes (in addition to walks). Generally, the more exercise, the better, but only to a certain extent, and this is a separate topic. Here we speak about the required minimum.

Also, if there are no serious cardio-vascular problems, it is useful to make short periods of intensive exercise, bringing it to the anaerobic level. Such periods should last from 1 to 4 minutes, and 2 to 4 of them per day, with intervals between them at least 3 to 5 minutes, will be enough (maybe, not enough for somebody, like athletes, who needs results in competitions rather than maintenance of health). If the heart rate at the end of such periods exceeds 120-125 beats per minute (or doubles in comparison with the resting state), and shortness of breath appears, then the goal is achieved. This is called high-intensity interval training (HIIT). It gives one a "hormonal jolt" to the organism, which additionally helps to normalize operation of the system regulating metabolism. 

The process of repair of the broken system is reverse to the process of breaking it.

The normal body mass is determined by the body mass index (BMI). This is a rather imperfect index chosen because it requires simple measurements and calculations. It gives an approximate indication of the normal body mass. But individual peculiarities may vary in a wide range. There are people who, according to this index, have an excess body mass, but they are absolutely healthy. If the system of automatic regulation discussed here works normally, the organism automatically maintains the body mass optimal for itself. 

The goal "to lose weight" is wrong. It is difficult to achieve and almost impossible to maintain without repairing the system. Besides, not all of those whose metabolic system is broken really need to lose weight. The right goal is to repair the metabolic system. And, whether we need to lose weight or not, our organism will decide on its own and will adjust our body mass accordingly as soon as the broken system starts being repaired.

Calories stored in glucose can always be spent, while calories stored in fats, only when the insulin level is not too high. When insulin is too high, calories in fats are not spent, and are only accumulated. When the system is broken, most of the time, or all the time, the insulin level is so high that the organism cannot spend calories stored in fats. In a system that works properly, the insulin level is sufficiently low most of the time and does not block expenditure of fats. But, of course, a too low or zero insulin level means type one diabetes.

The main measures for the repair: 1) limitation of consumption of carbohydrates and replacement of them by an increased consumption of fats, especially saturated ones; 2) one large interval per day between meals – at least 12 hours, but much better, 16 to 18 hours, or even just one meal a day (OMAD). Physical exercise and activities are very important, not only and not as much for spending energy. Motion is life.

There are exceptional cases, when attempts to repair the metabolic system cause catastrophic consequences. Usually they are related to abnormal operation of other systems or the same system, caused by serious diseases or traumas.

Intermittent fasting, in addition to restoration of the ability of the organism to use fats as a fuel, also initiates autophagy and increases production of the human growth hormone. But one should be careful when refraining from eating for a long time – to maintain the balance of electrolytes when fasting longer than 24 hours and to think of being under a medical observation when fasting for more than 3 or 4 days, especially for the first time.

Physical activity is a powerful stimulator of the brain. Low-intensity activity is aerobic – ATP molecules are charged by mitochondria with the use of oxygen. At high intensity, they become anaerobic – mitochondria cannot keep up with the increased demand for recharging ATP, and fermentation became involved for charging ATP without oxygen. Simple morning exercise and walking at a moderate speed for one to two hours a day will provide the minimum physical activity.  Also, if there are no serious cardio-vascular diseases, it is useful to practice HIIT – high intensity interval training – two to four periods per day, each lasting from 1 to 4 minutes, and with intervals between them no less than 3 to 5 minutes.