Energy… what is it?

When it comes to sports, energy is a difficult topic to avoid. Whether it's endurance, running, swimming, weightlifting, or powerlifting, progressive or maximal energy release is one of the most common sports challenges. Yet athletes are often unsure how their muscles store or release energy. a large amount of energy .

This article will give you a clearer and simplified idea of ​​the processes that allow you to store and release muscle energy. A complex mechanism, your muscle cells generate energy with adenosine triphosphate. More simply, let's say that ATP is a phosphate transporter. Phosphates then release cellular energy. This also explains why phosphorus is one of the most abundant minerals in the human body. Other complex mechanisms allow our cells to obtain energy. However, these complex processes that take place at the mitochondria level are beyond the scope of this article. Just remember that Adenosine triphosphate is one of the simplest biological processes to describe and understand.

Talking about energy means talking about glucose and energy substrates

An energy substrate is a simple substance, such as glucose, an amino acid, or a fatty acid, that allows you to end up with an energy molecule called ATP or Adenosine triphosphate . Indeed, glucose is the simplest molecule for your muscles to transform into ATP. Adenosine triphosphate is not, however, an energy molecule strictly speaking, but a reserve of phosphates ( triphosphate or three phosphates ) which generates a release of energy. By releasing ATP, a phosphate produces energy, which allows your cells to live and activate, as muscle cells do.

Adenosine releases a phosphate to produce muscle energy and generate force

However, when ATP has lost a phosphate to produce energy, it becomes inactive. This is called ADP ( adenosine diphosphate ). Fortunately, the phosphocreatine is also rich in phosphates. It then gives up one of its phosphates to ADP and the latter returns to its initial form of ATP. This process between creatine and ATP is valid during the first seconds of exercise , we then speak of anaerobic alactic because it is a release of energy without the help of oxygen and without the production of lactates (or lactic acid for a very brief moment, if it really exists at the cellular level). At this level, it is still an exchange between ATP and creatine , but this energy-generating process doesn't last more than a few seconds. In fact, nature is well made and your body has many resources for generating energy.

The Krebs cycle creates ATP and intermediates such as lactate, pyruvate, and alpha-ketoglutarate.

One of these processes is called the Krebs cycle, named after the person who formalized this cellular process. In reality, the Krebs cycle ( or citric acid cycle ) produces little ATP but it mainly allows the formation of intermediate molecules, including the lactates we have just mentioned. Alpha ketoglutarate, acetyl CoA and other molecules are also created during this cycle… From there, the energy release Cellular activity can continue after the work of the ATP/phosphocreatine pair. Here, glucose already acts as a substrate for the formation of ATP.

The Krebs cycle alone does not produce adenosine triphosphate when energy needs increase due to exercise intensity. At this level, our mitochondria ( small ATP-producing factories ) will generate ATP with glucose and oxygen. This mechanism, called cellular respiration by oxidative phosphorylation, can ultimately generate more than 30 ATP. By this principle, the energy released by ATP then allows muscle contraction to continue for long periods, sometimes up to a marathon.

In strength training exercises that last only a minute or less, ATP/phosphocreatine exchanges and glycolysis (use of glucose) are the main focus. In contrast, endurance sports use a maximum amount of oxygen and glucose to create ATP with oxidative phosphorylation. This is how our muscles can cope with all the stresses. energy demands , from a weight training set that lasts only 40 seconds to a marathon or Iron Man that can last several hours. Also note that when energy demands are very intense, ATP can be broken down into ADP (adenosine diphosphate) and then into AMP (adenosine monophosphate), until only a metabolic waste product, ammonia, remains. However, the body always finds a way to call upon other sources of energy, even during the most intense workouts.

Where are our energy and glucose stores located?

Naturally, to generate energy for periods of several minutes or hours, our body must be able to store sufficient energy in the form of glucose. These glucose reserves are located in the muscle mass (for about 2% of the volume of our muscles) and in the liver . These are glycogen reserves, glucose chains linked to each other. However, liver glycogen will have a very difficult time fueling our muscles. However, when our glycogen stores are low, a hormone called glucagon is secreted. Glucose is then released by the liver. This mechanism helps raise blood glucose levels. Fortunately, our bodies can rely on other energy sources.

Amino acids and fats can serve as our energy reserves

Glucose isn't the only energy substrate used for ATP synthesis. Amino acids and fats are, too. Moreover, fatty acids are more energy-dense than glucose or amino acids. with an average caloric output of 9 calories per gram. However, amino acids cannot be stored as an energy reserve. However, if muscle glycogen drops too low, amino acids from your own muscles will serve as an energy source. This is called catabolism, another reason to never run out of carbohydrates. Most amino acids are called glucoformers. That is, they can be broken down into glucose. L-Alanine, BCAAs ( Leucine , Valine, Isoleucine ) and L-Glutamine are among the amino acids most easily used by the body to remake glucose. Your muscles contain more than 30% BCAAs, making them energy substrates favored by the muscles themselves. However, while your own proteins can serve as energy substrates, this situation is still quite rare, even if it is completely normal.

Fats (or fatty acids) are also among the sources of energy preferred by your muscles when glycogen is running low. Each gram of fat releases 9 calories compared to 4 for carbohydrates or amino acids. MCTs are an exception with 7 calories. Your blood also contains triglycerides which will be used as an energy source when the exercise is particularly long. Finally, the three Macronutrients are used by your cells to generate energy. Carbohydrates ( stored as glycogen ), amino acids, and fatty acids all contribute to the synthesis of ATP by your muscle cells during exercise.