Why exercise works wonders

An active lifestyle benefits us for many reasons, apart from the known reasons

We all know we should exercise, but few realize that exercise is the single most important thing most of us can do to improve or maintain our health. Regular movement not only reduces the risk of developing heart disease, stroke and diabetes and causing death as a result, but also prevents certain types of cancer, improves mood, builds bones, strengthens muscles, develops lung capacity, reduces the risk of falls and fractures, and helps to control excess weight - and these are only some of the better known effects.

Many studies conducted in recent years have revealed additional benefits. Among other things, it seems that physical activity strengthens the brain's abilities, especially the ability to perform tasks that require attention, organization and planning. Among some of the population, it reduces symptoms of depression and anxiety and improves the immune system's ability to recognize certain types of cancer and fight them. Also, besides describing the general health benefits of regular physical activity, researchers are beginning to detail the positive changes that occur at the level of cells and molecules in diseases such as atherosclerosis and diabetes.

Studies designed to examine the effects of physical activity, large and small, on various systems in the human body (the heart and blood vessels, the digestive system, the endocrine system and the nervous system, among others) show that the benefits derive, apparently, from a variety of moderate improvements in physiology, and this is contrary to the idea of ​​positive effects large on a small number of processes in certain cells and tissues.

The researchers also realized that people do not have to compete in triathlons to enjoy the benefits of physical training. Twenty years ago, health experts focused almost exclusively on the benefits of vigorous activity. Today, however, they emphasize the value of prolonged moderate movement. In extensive studies in the field of women's health, one of us (Manson) showed that moderate activity has benefits that can be compared to those of vigorous activity. Based on the data from these and other studies, the current US physical activity guidelines (published in 2008) recommend moderate activity, such as brisk walking for at least 30 minutes, five times a week or more, or 75 minutes of vigorous activity, such as jogging, once per week as well as 30 minutes of muscle strengthening activity at least twice a week.

A closer look at some of the most exciting findings reveals the unexpected ways in which exercise protects our bodies and keeps them functioning properly.

Immediate effects

To fully understand the latest findings, it is useful to know the body's typical response to increased physical demands. Physical training can be different from person to person. It can take different forms, such as walking in the snow, swimming or brisk walking on the beach, and in each of them be at a different level of effort. It is the aerobic training that greatly increases the amount of oxygen that the muscles consume, and therefore requires the lungs to work hard. Its health benefits are also the most understandable. However, there is also room for less mobile training, such as weight lifting and balance exercises.

Scientists have developed fairly accurate methods for measuring the intensity of aerobic exercise in research laboratories. Outside of the lab, an effective and much less expensive way to measure how much you exert your body is the speech test: moderate activity begins when your heart rate accelerates, and you breathe more heavily. If you are able to speak or recite while moving, you are still at a moderate intensity level. On the other hand, if you can only croak a word or two at a time, this is a vigorous workout. On the other side of the scale, if you are able to sing right on the move, your training intensity is low.

Every time a person increases the training rate, his nervous system prepares all the organs of the body for action. Initially, the exerciser may feel increased awareness, high heart rate, accelerated breathing and light sweating. Inside the body, blood flow decreases to organs that are not essential for movement, such as the digestive system and kidneys. On the other hand, the blood vessels in the active muscles expand and ensure that a sufficient amount of oxygen-rich blood flows to the place where the greatest effort occurs.

Inside the muscle cells, the oxygen diffuses into cellular structures called mitochondria, which are used to produce energy for the cell's needs. The fuel at the base of this process is the sugar molecule glucose, which the body produces by breaking down larger pieces of food and is absorbed during digestion. The connection of oxygen to glucose in the mitochondria causes a particularly efficient combustion-like process: in the presence of oxygen, the mitochondrial bodies are able to produce almost 20 times more energy from each glucose molecule than without it.

The first glucose molecules that the body burns are molecules that are stored in a compound called glycogen, and is found mainly in the liver and muscles. But as training progresses, the available glycogen stores run out and triglyceride molecules (a type of fat) become the main fuel source. This internal combustion creates certain byproducts, such as lactic acid and carbon dioxide, which seep from the muscle into the bloodstream. When this happens, the rest of the body starts to feel them. The increasing concentration of these waste materials triggers additional biochemical reactions in the brain, lungs and heart, until eventually getting rid of these compounds becomes more efficient and less tiring.

The benefits of physical training begin to accumulate to a considerable extent as soon as physical activity becomes a regular habit. The body adapts to the increasing demands placed on it, and endurance increases as the person "gets in shape". For example, the lungs process more oxygen as breaths become deeper, and the heart pumps out more oxygen with each beat. Such an adaptation, which usually begins to appear within a few weeks of following the physical training guidelines, also causes biological changes that improve long-term health.

molecular changes

Entire libraries could be filled with data showing the effects of physical activity on everything from major organ systems to turning certain genes on and off. We will focus on some of the recently discovered mechanisms that help explain why physical activity improves our cognitive abilities, increases our ability to control blood sugar levels and strengthens the cardiovascular system. These changes have a greater impact on quality of life that outweighs almost any other benefit of exercise.

Athletes have always known that training improves their mood and mental health. However, it was only in 2008 that scientists were able to directly measure the runners' "high" feeling: a feeling of euphoria that appears after a long workout. They discovered that during long runs, not only does the brain release more endorphins (opium-like hormones that induce a pleasant feeling), but they also determined that these compounds are active in certain areas of the brain responsible for strong emotions. Before that, studies identified the increase in the level of endorphins only in the bloodstream, regardless of changes in the brain.

Recently, researchers have focused on the chemical changes in the brain that are caused by training and improve our ability to concentrate, think and make decisions. In 2011, a rigorous scientific experiment was conducted, which included random division into groups of 120 subjects in their 60s and 70s. This experiment showed that physical training increased an area of ​​the brain called the hippocampus. The researchers noted that the particular part of the hippocampus that was affected by the training is what allows people to remember familiar environments. It is also one of the only areas of the brain that produces new nerve cells - at least in laboratory mice. It is commonly thought that new neurons help distinguish between similar but separate events and objects. Animal studies have also shown that exercise increases levels of the chemical compound responsible for encouraging the growth of these new nerve cells: a molecule known as brain-derived neurotrophic factor, or BDNF.

Now, research is challenging the conventional wisdom about how exercise prevents heart disease. In the past, scientists believed that regular activity reduces the risk of these diseases mainly by reducing blood pressure and reducing the amount of LDL cholesterol (the "bad" cholesterol) while increasing the amount of HDL ("good") cholesterol in the blood. This conclusion is only partially true. Although, for some people, training greatly reduces blood pressure, but for the majority, this benefit is relatively small. Also, certain types of training, especially resistance training, such as weight lifting, can raise the HDL level, in a process that may take months and whose effect is modest, on the order of only a few percent.

Other studies have found that the more important effect associated with LDL is how exercise changes the properties of the molecule itself rather than its amount in the blood. From a technical point of view, the LDL is not just cholesterol, but a chemical array that carries the cholesterol in the bloodstream, like a vehicle that carries deliveries from the grocery store. Since cholesterol is a fatty substance, it is not able to dissolve in the aqueous environment of the blood and needs to be packaged in substances capable of doing so. The LDL clusters themselves are found in a variety of sizes, similar to scooters, cars and trucks that transport products.

In recent years, some scientists have discovered that the small LDL clusters are particularly dangerous. Among other things, they have a tendency to lose electrons, which pass to other molecules in the blood vessels and damage them and the cells where they are found (imagine a wild driver in a shabby delivery vehicle). In contrast, the larger LDL aggregates are also chemically more stable and cruise through the bloodstream without harming anything (like well-maintained trucks with professional drivers).

According to the studies, physical training increases the number of large and safe LDL clusters, decreases the number of the small and dangerous ones, and generates all of this by increasing the activity of an enzyme called lipoprotein lipase found in fatty tissues and muscle tissues. Two people with the same amount of cholesterol in their blood but with different levels of physical activity may therefore be at very different risk of heart disease. A lazy person will likely have many small and few large LDL aggregates, if any, while the active person's blood will have mostly large LDL aggregates. The cholesterol level, as mentioned, is the same, but the lazy person will have a much greater chance of a heart attack than the active person.

Regular physical activity has a positive effect on another key component in the blood: the sugar glucose. The liver, pancreas, and skeletal muscles (which move the head, arms, legs, and upper body) usually work together to ensure that every part of the body gets the sugar it needs, whether the person is at rest or active. By definition, the activity puts more strain on the skeletal muscles, and therefore they need more glucose. In the long term, the activity makes the fibers inside the muscle more efficient in using glucose, and thus the muscle becomes stronger.

The liver immediately responds to the call for additional fuel and releases sugar molecules into the bloodstream. The pancreas releases the hormone insulin, which instructs the cells to absorb a greater amount of glucose from the blood. Apparently, such a process can cause sharp fluctuations in sugar levels, especially after a meal or a run. But in practice, the body works hard to maintain blood sugar levels within a fairly limited range, between 70 and 140 milligrams per 100 milliliters, and in a fasting state much less than 126, at least in non-diabetics. One of the reasons for maintaining a sugar level of more than 70 mg per 100 ml is that glucose is the main source of energy for the brain, and therefore the brain is very sensitive to any change in the amount of glucose in the blood. Extremely low levels can cause coma and death within minutes. It is equally important from a physiological point of view to avoid too long periods at the upper end of the scale. Excess blood sugar burdens the system and causes cells to age prematurely.

When exercise becomes a daily habit, the muscles become more sensitive to the effects of insulin. This means that the pancreas no longer has to work hard to maintain normal sugar levels: a smaller amount of insulin will achieve the same result as larger amounts were consumed before. This ability, to do more with less investment, is especially beneficial for those suffering from type 2 diabetes, whose body has difficulty maintaining normal sugar levels mainly because it becomes resistant to the effects of the hormone. Insulin also encourages proliferation, or faster production of new cells, so its high levels are associated with a higher risk of cancer, especially of the breast and colon. [On the link between insulin and obesity, see "Why do we get fat?" in this issue.]

Recently, it was also discovered that physical activity improves the absorption of glucose in another way, which does not require the presence of insulin. The existence of a second path to remove glucose from the blood into the muscle cells can open the door to new treatments for diabetes.

The greatest benefits for diabetics are achieved from a combination of different types of exercise. Two clinical studies, which randomly divided subjects into groups, reported that a combination of aerobic training and resistance training was more beneficial in maintaining blood glucose levels than either type alone. However, the first study was conducted so that it is difficult to know whether the benefit is due to the combination of the types of training or the fact that the subjects who trained in the combined training actually performed a longer activity than the other subjects. One of us (Church) decided to examine the question through a follow-up study with the participation of 262 diabetic men and women who were less active. They were divided into four groups: an aerobic group (which exercised on a treadmill), a resistance group (rowing machine, pushing weights with the legs, etc.), a combined group and a control group, which performed weekly flexibility and relaxation classes.

All the groups that performed physical activity spent the same amount of effort and time (about 140 minutes per week) over the course of nine months. Everyone reduced their weight, and the physical fitness of both groups that performed aerobic activity improved. In contrast, only the group that performed combined training showed a significant decrease in the amount of HbA1c protein in the blood. This protein is used as a marker of the average blood sugar level in recent months. The advantage of combined training dictates that each type of training affects other physiological mechanisms, an idea that currently guides researchers at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, and elsewhere.

Another way in which continuous training strengthens muscles is by increasing the creation of energy-producing mitochondria. In response to the regular training, the muscle cells begin to produce a protein called PGC-1α, which causes the cells to produce new mitochondrial bodies. And so each cell is able to convert more glucose into energy, and the entire muscle becomes stronger and resistant to fatigue.

Dangerous sitting

In light of all the health benefits of moderate exercise, one would think that everyone would lace up their sneakers and leave the house by now. But in practice, many are not as active as recommended, not even for half an hour of moderate activity, five days a week. Only 52% of the adult population in the US are active enough to meet these requirements, and only 29% strengthen their muscles as recommended, twice a week, for 30 minutes each time. Only one in five meets both the aerobic and resistance training recommendations.

The difficulty of changing habits prompted scientists to test whether short or even more moderate activity sequences also help health, with the hope that positive results will convince even the lazy to move a little more than usual. So far, the data shows that even minimal daily exercise can slightly extend life. An analysis of data from six studies, conducted in 2012 and including a 655,000-year follow-up of 11 US adults, found that people who spent even just 1.8 minutes a day in a relaxed activity (gardening, washing the car, walking around the neighborhood) lived, on average, 40 years longer ( after the age of 3.4) from those who were not active at all. People who met the moderate activity guidelines gained more: their life expectancy was 60 years longer, and those who were active for 90-4.2 minutes a day gained up to XNUMX years.

Even a minimal effort therefore has advantages, but an overall look at the research done so far in the field shows that it is better to increase the duration of the activity in any case: add moderate exercise to light exercise, or vigorous activity to a routine of moderate exercise. The worst news, as far as today's office workers are concerned, is that sitting for more than six hours a day can be harmful even to those who occasionally exercise at a high intensity. It is not yet known whether the problem lies in the yeshiva itself, or in the lack of activity that usually accompanies it.

In light of the ongoing and accumulating evidence regarding the health benefits of physical activity, the message is clear: prolonged and regular movement, at any level of intensity that they can safely withstand, should be incorporated into everyone's daily routine and physical environment. This activity should be as simple to perform as getting into the car.

We strongly recommend that doctors and other healthcare professionals provide exercise prescriptions at each routine visit. We also suggest that additional studies be conducted that examine behavioral programs, public health campaigns, and urban planning changes that may promote consistent levels of beneficial physical activity in our sedentary society.

__________________________________________________________________________________________________________________________________________________________________________

first steps:

In the 19th century, Edward Muybridge incorporated the stop-motion photography technique to study human movement.

About the authors

Shari S. Basuk (Bassuk) is an epidemiologist at Brigham Hospital and a researcher at Harvard Medical School.

Timothy S. Church (Church) is the John S. McIlney Endowed Chair, director of the Preventive Medicine Research Laboratory and professor at Louisiana State University's Pennington Biomedical Research Center.

Joan A. Manson (Manson) heads the Department of Preventive Medicine at Brigham Hospital, is a Professor of Medicine and Professor of Women's Health at Harvard Medical School, as well as a Professor in the Department of Epidemiology at the Harvard School of Public Health.

in brief

regular physical activity Moderate or vigorous exercise significantly reduces the risk of dying from heart disease, stroke, diabetes, cancer and other diseases.

Researchers recently identified Many previously unknown ways in which regular physical exercise can reduce the risk of heart disease and cancer, help control diabetes and even improve learning ability.

Long sitting, on the other hand, eliminates some of the health benefits that come from regular physical activity.

From the heart and lungs

The training also benefits less predictable systems in the body

Most people do not understand that performing regular physical activity, moderate or vigorous, completely changes our body inside and out. Here are some of the lesser known effects, starting with nerve connections in the brain and ending with the major muscles and bones of the limbs.

Nervous System

The training improves the cognitive functions. Aerobic training helps with organization, planning and attention, especially for adults.

immune system

Regular physical activity protects the body from inflammation; However, excess activity may weaken the immune system's ability to fight bacteria.

the endocrine system

Exercise improves the body's response to insulin and strengthens another hormone called adiponectin. These changes reduce the risk of type 2 diabetes and metabolic syndrome.

cancer

Physical activity reduces the risk of breast, colon and other cancers.

the skeletal muscle system

Weight training and balance exercises help prevent fractures and falls. Aerobic fitness reduces everyday fatigue by increasing muscle efficiency.

Genetics

Scientists are identifying the unique genes that are turned on or off due to changes in physical activity. These effects are often small, but occur in a wide variety of cells.

More on the subject

Global recommendations for physical activity to improve health, World Health Organization, 2010.
US government physical activity guidelines:

Scientific American online

Check your activity level against US standards at