urrent scientific research shows that if you train for hours every week, especially when it comes to medium-intensity endurance activities, there is no added value in improving "health and fitness". Movement at low intensity (e.g. hiking), on the other hand, is very healthy and should be included into your daily routine whenever possible (e.g. going for a walk over lunch, take the stairs instead of the elevator). Even more astonishing is the fact that such short, but intensive strength training sessions have a better effect on the cardiovascular system than training forms in the low or moderate intensity range (such as running or cycling at low or moderate intensities). At the same time, a large number of other elements of the metabolism are stimulated, which have unique health effects that cannot be achieved with conventional training. If you also consider that activities such as running often lead to a high level of physical wear and tear, then it seems senseless to expose yourself to this risk in order to improve your fitness and health [1,2,3,4,5,6].
STRENGTH TRAINING MAY WELL BE HEALHY...BUT MOST OF YOU WILL SURELY ASK, HOW FOR GOD'S SAKE CAN I IMPROVE MY CARDIOVASCULAR SYSTEM AND MY OVERALL HEALTH WITH PURE STRENGTH TRAINING? IS THAT POSSIBLE AT ALL AND WITH JUST A FEW MINUTES PER WEEK?
Yes, it works. And to be able to answer the question better, we first have to distance ourselves from the question of how much sport and exercise we can potentially do and ask ourselves how little training is required to achieve positive results on fitness and health!
The results of various studies show a uniform and astonishing picture, since the total amount of training required is significantly lower than previously recommended [1,2,3,4,5,6]. For example, a 6-minute high-intensity strength training, which is performed once a week, can achieve a higher increase in aerobic capacity (= Vo2max as a measure of fitness status) than a conventional low- or medium intensity endurance training, which also takes about 98% more time on average.
First of all you have to understand that mechanical work is mechanical work: This means that our organs, such as the heart and lungs, cannot distinguish whether our muscles are used when jogging or on the leg press. Heart and lungs only know how high the current energy requirement is and try to meet it. Accordingly, it does not matter whether a 30-second, intensive muscle effort exclusively strains the lower body, e.g. when cycling or the upper body like doing pull-ups. Both scenarios involve mechanical work that our muscles do. And this mechanical work is the key factor for all metabolic processes that take place in our cells.
To come back to the question of how a training approach that takes up only 2% of the time of a conventional workout achieves the same or even better aerobic (cardiovascular) performance increases, one can give a simple answer: Intensive strength training is a very large muscle effort that triggers a very high stimulus. Conversely, the greater the muscular effort, the shorter the necessary duration of the activity. As a result, it is now important to understand that a sprint session (but also a strength exercise with far less risk of injury) that can be sustained for a maximum of 60 seconds is a better cardiovascular stimulus than a 60-minute endurance run. The reason for this is that all types of muscle fibers are exposed to a greater total load, as well as the energy systems that support our muscles. This is not the case with low- or medium-intensity activities and the stimulus is too small to cause all positive adaptations to fitness and health.
⟶ Read more about our muscle fibers...
If you look at our metabolism in detail, it clearly shows that conventional aerobic training is a low-intensity physical activity in which the mitochondria do their work at a submaximal pace. And that means that only a part of the metabolism - the aerobic system- is activated to generate energy. Nonetheless, innumerable health-promoting effects have been associated with this very specific metabolic adaptation over several decades. The difference between aerobic and cardiovascular conditioning (aerobic) soon became blurred, and the two terms were considered synonymous. But you should keep in mind that the cardiovascular system is always active. Even when you are sitting at the office table and talking to someone on the phone. So you always do "cardio" when you do something - but also when you don't do anything. The heart and blood vessels support the cell as a whole. If you also look at the interrelationships between the different metabolic cycles, it becomes clear that you can never clearly separate them, they always run simultaneously and in combination. Accordingly, each component of metabolism is directly related to the cardiovascular system. Strength training is actually the best way to not only train the cardiovascular system, but also to achieve various other positive health effects that no other form of training can achieve. This is because, in contrast to aerobic training, high-intensity strength training involves all components of the metabolism and stimulates them to function more efficiently, both the metabolism in the cytosol (the liquid part of the cell, without oxygen) and the metabolism in the mitochondria (i.e. with oxygen). It is also important to understand that the necessary auxiliary systems (including the aerobic system) will only adapt to new requirements with increasing muscle strength. This explains, among other things, why many people, as they lose muscle mass with increasing age (an aging process known as sarcopenia), not only lose strength, but also endurance with often serious health consequences.
In order for a muscle to do contraction work, it needs energy. The process that is responsible for mobilizing, transporting and providing energy in the muscle cells is called metabolism (also called energy metabolism or energy supply) and takes place in our cells.
There are basically two different mechanisms available for this energy supply. Firstly, the aerobic energy supply , in which energy is released while consuming oxygen. This takes place in the so-called mitochondria, our cell power plants.
And on the other hand the anaerobic energy supply (without the aid of oxygen), in which lactic acid (lactate) is produced and which takes place outside the mitochondria in the so-called cytoplasm. Since this energy supply takes place in our cells, which is connected to our cardiovascular system via the bloodstream, it is impossible to consider individual metabolic processes such as the aerobic and anaerobic mechanism in isolation. For this very reason, the overall performance of the cardiovascular system can only be improved if all components of the metabolic activity within the body cells are optimized. Unfortunately, this is exactly what happens with low- or medium intensity endurance training...various components of metabolic activity are neglected and the cardiovascular system is also not optimally trained.
Back to the metabolism:
In a first step, energy enters our cells in the form of glucose, a sugar that is obtained by breaking down food (the body's preferred macronutrient for the production of glucose are carbohydrates, but the body can also derive glucose from other organic substances, if insufficient carbohydrates are ingested). Once the glucose has entered the cell, it is processed through approximately 20 chemical reactions until it has turned into a substance called pyruvate. This process takes place in the context of anaerobic energy generation. The pyruvate is then transported to the mitochondria, which metabolize it in a complex process through the citrate cycle and the respiratory chain. Here, pyruvate is converted into a total of 36 ATP molecules (ATP = adenosine triphosphate, the storage form of energy that enables metabolic processes in the first place). This process is known as aerobic energy supply.
The citrate cycle and the respiratory chain can generate a lot of energy in the form of ATP, but they run comparatively slowly. In contrast, glycolysis (a process in which glucose is converted into pyruvate in a few steps in the cytosol) produces only two ATP molecules, but it does so much faster than the citrate cycle and the respiratory chain, which is essential in a life-threatening situation or in extreme exhaustion. If you are well conditioned, in such an emergency, this glycolytic cycle can be accelerated and the active muscles can be supplied with energy over a longer period of time. Because this way more pyruvate is formed than can be consumed in the aerobic cycle (in the mitochondria), pyruvate accumulates and is converted into a substance called lactate by the so-called lactate dehydrogenase. If such a situation persists, lactic acidosis develops, which manifests itself in muscle burning and ultimately leads to the fact that the activity has to be stopped when the lactate level exceeds a certain threshold. However, it is also possible to generate new fuel for the working muscles from the lactate, which enters the blood and thus the liver via the muscles. This happens in the liver, which converts lactate back into pyruvate, before new glucose is generated as an energy supplier via gluconeogenesis (this cycle is also known as the Cori cycle).
The citrate cycle and the respiratory chaincan generate a lot of energy in the form of ATP, but they run comparatively slowly. In contrast, glycolysis - a process in which glucose is converted into pyruvate in a few steps in the cytosol - produces only two ATP molecules, but it does so much faster than the citrate cycle and the respiratory chain, which is in a life-threatening situation or in the event of extreme exhaustion. If you are well conditioned, this glycolytic cycle can be accelerated in such an emergency and the active muscles can be supplied with energy over a longer period of time. Because this way more pyruvate is formed than can be consumed in the aerobic cycle (in the mitochondria),Lactate converted. If such a situation persists , lactic acidosis develops , which manifests itself in muscle burning and ultimately leads to the fact that the activity has to be stopped when the lactate level exceeds a certain threshold. However, it is also possible to generate new fuel for the working muscles from the lactate, which enters the blood and thus the liver via the muscles. This happens in the liver, which converts lactate back into pyruvate, before new glucose is generated as an energy supplier via gluconeogenesis (this cycle is also known as the cori cycle).
It is now important to understand that only anaerobic training (i.e. high-intensity training) stimulates glycolysis. And this is the only way to achieve that more pyruvate is produced at a higher speed, which in turn massively stimulates the citrate cycle. So if you only do a low-intensity (submaximal) training, it is not possible to make optimal use of the aerobic cycle. After a high-intensity muscle effort, lactate accumulates in our muscles during the recovery phase. The cell processes the lactate by converting it back into pyruvate, which then reaches the mitochondria, where it is subsequently metabolized aerobically. This means that, especially during the recovery phase after a high intensity workout, there is greater stimulation of the aerobic system, than you get with conventional, low- or medium intensity training. Although many people still believe that the accumulation of lactate is a sign that the aerobic metabolic pathway works only suboptimally, the reality is that glycolysis always produces pyruvate faster than it can be used in the citrate cycle. The enzyme pyruvate dehydrogenase (which transports the pyruvate to the mitochondria for processing via citrate cycle) is known as a speed-limiting enzyme, which means that its reaction rate is fixed. As a result, it cannot be made to work faster and will always be slower than the other metabolic steps in this cycle, no matter how "aerobic" you are. So it is a fact that you always produce lactate when you exert yourself physically. In other words, lactate is not something that could be avoided in any way.
The lactate formed by a high-intensity activity can even be used constructively to increase our aerobic capacity. It is important to understand that the aerobic system always works best when you are recovering from lactic acidosis. After a highly intensive workout, the body is still busy for a while to break down the pyruvate in the system - and that is exactly what happens with the help of aerobic part of the energy metabolism. In addition, hydrogen ions are released into the blood whenever lactate is formed (if you train at a sufficient intensity).
There they interact with the hemoglobin molecules to change their shape so that they lose their affinity for oxygen. This leads to better oxygen release into the tissue. So if you train regularly with adequate intensity, this leads to the synthesis of a substance called 2,3-diphosphoglycerate (2,3 DPG) . For people who live far above sea level (Bohr effect) and for those who regularly do high intensity training (--> oxygen requirement exceeds the currently available amount) more 2,3-DPG is synthesized. This is another metabolic adaptation that only high-intensity training can achieve and that is extremely important for survival and physical functioning.
Another important and still misunderstood metabolic adaptation, which takes place during high-intensity training, is the fatty acid metabolism. Energy that the body does not need at the moment is stored in the form of triacylglycerol in the adipocytes (fat cells). When the body is under stress and needs energy (e.g. during muscular exertion or in emergency situations) the hormones adrenaline and glucagon stimulate the mobilization of triacylglycerol by activating the enzyme "hormone-sensitive lipase". Hormone-sensitive lipase releases fatty acids into the blood, where they combine to form a protein called albumin. Albumin transports these fatty acids into the muscles, where they undergo the so called B-oxidation and form 35 ATP molecules. In addition, glycerin, an intermediate product that arises during this process, can be passed into the liver and is converted into glucose, which is then further oxidatively processed and produces impressive 96 ATP molecules. This lively metabolic activity is only achieved through high-intensity training and is crucial for our survival as well as for our physical functioning. This should once and for all invalidate the myth that you do not burn fat during high-intensity training.
⟶ Read more about HIT and our fat metabolism...
Another unique metabolic adaptation that takes place during high-intensity training is the splitting of glycogen to generate energy in the skeletal muscles - the so-called glycogenolysis. The reason why this is so unique is that high-intensity strength training restores the insulin sensitivity of muscle cells (which are by far the largest glycogen store in the body). On average, men store about 70 grams of glycogen in the liver and about 210 to 220 grams in the skeletal muscles; in women it is about 20% less. While the glycogen in the muscle cells is only used there, the glycogen in the liver serves to maintain glucose homeostasis in the blood, which is regulated in the long term by a balanced ratio of insulin and glucagon.
When we were hunter-gatherers, we were most vulnerable while consuming food. As a result, we developed a mechanism that still enables us to activate our metabolism in a matter of seconds. This is exactly what is achieved by glycogenolysis in our skeletal muscles. In emergency situations, the glycogen that is stored in our muscles is immediately broken down and used on site to generate energy. High-intensity training can artificially trigger such an emergency situation and mobilize the glycogen stores. The reason for this is that muscle fibers, which are otherwise only used in an emergency situation (such as during an attack or flight), are also activated during high-intensity strength training. In addition, these muscle fibers stimulate the release of stress hormones such as adrenaline and noradrenaline . In such emergency situations, the muscle cells' glycogen stores empty almost completely, which means that insulin acts on the cell surface and ensures that a supply of glucose gets into the muscle. In addition, the same process that activates glycogenolysis also activates hormone-sensitive lipase and the mobilization of fatty acids for energy. So this means that during high-intensity training, both glucose and fatty acids are released into the blood. The blood transports them to the liver for B-oxidation and then they are brought into the mitochondria to produce a impressive 96 ATP molecules.
Many people try to control their insulin levels solely through their diet. This is a very important step and is achieved through a good balance between insulin and glucagon. But it is very important that a healthy diet is consistently pursued over the long term. Unfortunately, there is no amplification or signal amplification via nutrition as with a high-intensity training. High-intensity strength training brings about a superior adaptation of the metabolism because it triggers both the mobilization of glycogen and hormone-sensitive lipase - through the so-called reinforcement cascade. In such an amplification cascade, a certain enzyme (or hormone) activates a number of other enzymes instead of producing a metabolic effect on its own, as is the case with a glucagon molecule, for example, which switches on and triggers the release of only one glucose molecule from the glycogen. At the next stage of the amplification cascade, a large number or even hundreds of enzymes can be activated. Each of these hundred enzymes in turn activates another stage of the cascade and so on. So instead of just pulling one glucose molecule after the other from the glycogen chain, the activity of an enzyme increases exponentially, so that thousands of molecules are now split up at the same time to generate energy. For this very reason, the emptying of glycogen stores, which is triggered by heavy muscle strain, is enormously accelerated and expanded [17].
Nature has given us this highly effective mechanism to provide our muscles with a large amount of energy as quickly as possible in an emergency by using a series of enzymes that trigger a kind of avalanche effect. (At the same time, while the cascade of fortifications breaks down glycogen for further use, another enzyme that is involved in the formation of glycogen prevents the body from regenerating glycogen. Thus, all of the body's energy systems can work towards breaking down the available glycogen and using glucose as energy. This means that as long as the available glycogen is used up, the glycogen stores are not refilled.) This means that as long as the available glycogen is used up, the glycogen stores are not refilled. Through glycogenolysis and the resulting reinforcement cascade, high-intensity training attacks the largest glucose stores in our body and mobilizes them to such an extent that the resulting glucose deficiency must be remedied after the training. This creates a situation in which the insulin receptors on the surface of the muscle cells become more sensitive and react more strongly to eliminate such a deficiency. Depending on how empty the stores are, it can take several days to replenish the reserves. The replenishment process proceeds through normal glycogen synthesis, which uses no comparable enhancement mechanism. Due to the considerable emptying of the glycogen stores with high intensity training, insulin sensitivity remains much longer after the workout than with any other forms of training (such as a 60-minute low-intensity endurance run that hardly empties the glucose stores at all). However, it is not only the insulin sensitivity per se that is important, but also the effects that this process has on the metabolism. As soon as the glycogen stores are completely filled, the glycolysis is inhibited because glucose accumulates in the body. A high glucose level leads to an abundance of metabolic by-products that inhibit the further use of glucose as an energy source. And that has serious consequences: If the glycogen stores are completely filled, glucose can no longer be processed via glycogen synthesis. As a result, excess glucose is stored as a fat reserve. When the glucose level is high and the glycogen stores are full, the enzyme phosphofructokinase (which is involved in the metabolism of glucose) is also inhibited. The glucose now only reaches fructose-6-phosphate in the glycolysis cycle, then it is directed to the pentose phosphate pathway, which converts the glucose into glyceraldehyde-3-phosphate (GP3), a precursor of fat, through a series of steps. Then several metabolic processes take place, the end result of which is the formation of a coenzyme called NADH, which serves to stimulate the synthesis of fatty acids. Full glycogen stores, which are associated with an increased carbohydrate intake, even stimulate the production of fatty acids, especially in the liver. This, in turn, drives up the amount of very low density lipoprotein (VLDL) because it is the first thing that is converted from glucose to fat. This very low density lipoprotein is converted to LDL cholesterol, which is an indicator of potential heart disease.
It remains the realization that low- or medium intensity forms of training are unable to activate the fast-contracting muscle fibers that store the most glycogen. As a result, the glucose reserves in the muscles never empty. The glucose in the blood doesn't know "where o go" and is ultimately stored in the form of body fat. This causes the muscle cell walls to lose their insulin sensitivity. The cell walls become inflamed due to the large amounts of insulin that the body has produced to cope with the high glucose levels. The body finally fights this inflammation with LDL cholesterol, which ultimately exposes the low- to medium intensity athlete to a higher cardiovascular risk. This may sound contradictory at first, but the cell, which is already full to the brim with glucose / glycogen, lowers its insulin sensitivity to protect itself from being flooded with even more glucose. Because too much glucose leads to saccharification of the cell and thus impairs its functionality. In addition, the metabolism of excess glucose produces oxidative free radicals, which cause strong inflammatory reactions. The same applies to "too much" insulin, which ultimately also causes inflammation on the vessel walls. (And here, too, the body tries to suppress deposits with LDL cholesterol.)
In summary, these processes of our metabolism clearly show why high intensity strength training is the best way to optimize all components of metabolic activity.
Sources:
Hi, I am a guest contributor & scientific advisor for the post-injury rehabilitation at AURUM. I specialize in orthopaedic surgery and traumatology with a focus on knee and shoulder surgery & sport traumatology. I hope you enjoy my articles. Feel free to get in touch with me for a consultation or second opinion.
See All Posts
