Strength and Its Reserves in the Body

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Nourishment sources of energy

Energy is a necessary factor for human life and is provided through nourishment. The unit of energy is kilocalorie, and one kilocalorie is the amount of heat required to raise the temperature of 1 gram of water by 1°C. Most of the energy sources come from the following nutrients: carbohydrates (4 kcal or 17 kJ per gram), proteins (4 kcal or 17 kJ per gram), and fats (9 kcal or 37 kJ per gram). Carbohydrates are the primary source of energy in human nourishment, and the most significant amount of these nutrients can be found in bread, rice, and pasta. Proteins are an essential nutrient for the human body, and good sources of protein include meat, fish, and eggs. Fats are also an essential nutrient, and the best sources of fats are plant oils. Vitamins and minerals do not provide energy but are essential for the proper functioning of the body. The energy content of individual foods varies, and individuals with a more active lifestyle require more energy. The best source of energy for humans is carbohydrates, and a balanced diet should contain different types of these nutrients.

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Is this truly the process by which we acquire energy from food?

Upon ingesting food, it remains in the stomach for a certain period. There, under the influence of digestive juices, the digestion process initiates. This process occurs in the small intestine, where food components disintegrate into smaller units, enabling their absorption through the intestinal walls into the bloodstream. At this point, the body can utilize nutrients to generate energy, which is produced and stored in the form of ATP. The ATP molecule consists of adenosine and three phosphoric groups linked in series. Energy reserves are accumulated in chemical compounds between phosphate groups. To release energy, one phosphate group must detach, i.e., ATP disintegrates to ADP. ATP plays a crucial role in energy and metabolic processes within the body. It serves as the universal energy source for all biochemical processes and the primary energy carrier within the cell. Each cell contains a limited ATP supply, typically consumed within a few seconds. To convert ADP back into ATP, energy is required, which arises from the oxidation of carbohydrates, proteins, and fatty acids within cells.

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Energy reserves in the body

After nutrients have been provided to the body, certain amounts of them are stored as energy reserves in the form of glycogen and fat. Glycogen, similar to other carbohydrates, is stored in limited quantities in the liver and muscle tissue. During physical activity, glycogen breaks down into glucose, which, together with fats and blood glucose, provides energy to the working muscles. The utilization of nutrients depends on the type and duration of exercise. Glycogen is composed of long chains of glucose molecules. If glycogen stores are sufficient, excess carbohydrates can be converted into fat. Proteins and amino acids typically serve as the body's energy source, but in situations of food scarcity and high energy demand, amino acids from muscle tissue can also serve as an energy source. Protein from food can serve as an energy source or be converted into fat only when it has fulfilled its structural function.

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How is energy utilized during physical exercise?

At the start of exercise or when energy consumption rapidly rises (such as during a sprint), the energy requirement is higher than the level at which ATP synthesis occurs through the oxidation of carbohydrates. The first source of energy is carbohydrates, which are burned without oxygen (anaerobically). This process is accompanied by the production of lactic acid, which allows the release of a certain amount of ATP. Although the amount of released ATP is significantly smaller than during aerobic exercise, the process is much faster. The second fast source of energy is phosphoric acid, which is present in small amounts in muscle tissue. During the breakdown of phosphoric acid, energy is released that is necessary for the conversion of ADP to ATP. This process is very fast, and the body's reserves of phosphoric acid last only 10-15 seconds. During this time, aerobic metabolism of carbohydrates occurs in the body, oxygen consumption from phosphoric acid ends, and lactic acid production stops. Fatty acids become available as an energy source for working muscles, and the conversion of ADP to ATP due to fatty acid oxidation increases. Between the fifth and fifteenth minute after starting exercise, the increased demand for ATP stabilizes.

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Energy sources used during physical strain

Carbohydrates are the most vital and necessary source of energy for working muscles and are indispensable for all types of physical activity. In the human body, as previously mentioned, carbohydrates are stored in small quantities as glycogen in the liver and muscles. During exercise, glycogen is depleted, along with fatty acids and blood glucose as a source of energy for muscles. Although fats provide more energy, their combustion process is considerably longer, and the synthesis of ATP through the release of fatty acids is maintained by utilizing carbohydrates and phosphocreatine. When carbohydrate stores are nearly depleted, the body cannot withstand intense loads.

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Restrictive factors impacting energy availability during workouts

Nutritional sources utilized in diverse forms of physical exertion phosphagens (ATP and phosphocreatine fueling maximal-effort explosive bouts under 10 seconds), muscle and liver glycogen (utilized via glycolytic pathways during intense resistance and interval training), and free fatty acids oxidized in mitochondria during prolonged, steady-state aerobic activities.

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Low intensity level

: the necessary extent of ADP to ATP conversion is relatively low and is achieved through the oxidation of fats, glucose, and glycogen. Once glycogen reserves are depleted, the importance of fats as an energy source increases. Considering that fatty acids are oxidized at a moderately slow pace, the duration of such a training session depends on the amount of glycogen in the body.

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Average intensity level

: when the physical exertion performed by the body reaches its peak to continue the oxygen oxidation process, there arises a need for immediate restoration of ATP reserves. Carbohydrates become the primary source of energy for the body. However, the ATP level cannot be sustained solely by the oxidation of carbohydrates, so there is also fat oxidation and lactic acid production.

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Ultimate level of exertion

:- The production of ATP is primarily sustained by the application of phosphocreatine and the emergence of lactic acid, as the metabolism of carbohydrate and lipid combustion cannot transpire at such a rapid pace.

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Duration of training sessions

The type of energy source is contingent on the length of the training sessions. Initially, energy is released by utilizing phosphocreatine. Subsequently, the body uses glycogen, which provides around 50-60% of the energy required for ATP synthesis. The remaining energy needed for ATP synthesis is obtained through the oxidation of free fatty acids and glucose. Once the glycogen reserves are depleted, fats become the primary energy source, and the utilization of glucose increases.

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Type of physical exertion where low-exertion periods are replaced by short, intense efforts

in actions where periods of relatively low load are suddenly replaced by brief, very intense exertions (e.g. basketball), phosphocreatin and glycogen are alternately utilized as the primary energy source in ATP synthesis, while during the low-intensity phase, phosphocreatin levels in the body are renewed.

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Organism's preparation

The better prepared the organism is, the higher its ability to metabolize oxygen (fewer substances are converted into lactic acid) and the more efficient are the energy expenditures.. A prepared person performs exercises with lower energy costs than a beginner.

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Food consumption

The greater extent to which the level of glycogen reserves in the body is higher before starting exercise, the later the state of fatigue will occur. In order to increase glycogen stores, it is necessary to increase the consumption of foods rich in carbohydrates.