Muscles need energy to perform their functions. The Energy supply can be guaranteed in various ways through the breakdown and conversion of nutrients.
What is the energy supply?
The energy supply for activities of the muscle is possible in 4 different ways. They differ in terms of speed and the amount with which they can deliver energy. The intensity of muscle activity decides which of these processes is used to provide energy.
The various processes often run side by side. In the anaerobic (without oxygen) alactic (without lactate attack) process, the ATP storage (adenosine triphosphate) and the creatine phosphate storage provide energy for a short time. However, this is only sufficient for 6-10 seconds, for well-trained athletes for up to 15 seconds and is called up at maximum performance in the area of maximum, rapid strength and speed. All other processes require the presence of glucose or fatty acids. They deliver ATP (adenosine triphosphate) in various quantities through complete or incomplete degradation.
With anaerobic lactic energy supply, glycogen, the storage form of glucose, is broken down incompletely. Hence this process is also called anaerobic glycolysis. The result is lactate and little energy, which is sufficient for 15-45 seconds of intense performance, for top athletes for 60 seconds. For long-lasting, low-intensity sporting activities, the energy is obtained from the complete combustion of glucose or fatty acids in aerobic (with oxygen consumption) energy production processes that take place in the mitochondria of the muscle cells.
Function & task
Muscles need energy to perform their functions. They convert this into mechanical work to move joints or stabilize areas of the body. The mechanical efficiency is very low, however, as only about a third of the energy provided is used for the kinetic requirements. The rest is burned in the form of heat, which is either released to the outside or used to maintain body temperature.
Athletes for whom fast movements or those involving high physical exertion are important over a short period of time draw their energy from the energy stores that are located in the plasma of the muscle cells. Typical disciplines that meet these requirements are, for example, the 100 meter sprint, weightlifting or high jump.
Typical sporting activities that show a duration of 40 - 60 seconds under maximum possible performance are the 400 meter run, 500 meter speed skating or 1000 meter track cycling, but also a long final sprint at the end of an endurance race. The muscles obtain the energy for these activities from the anaerobic lactic energy metabolism. In addition to lactate, more hydrogen ions are produced, which gradually over-acidify the muscle and thus represent the limiting factor for this type of sporting activity.
In the case of long-term, low-intensity sporting activities, the energy must be constantly replenished without the occurrence of substances that lead to a breakdown. It does this by completely burning glucose and fatty acids obtained from carbohydrates and fats. In the end, both energy sources end up after various degradation stages as acetyl-coenzyme A in the citrate cycle, where they are degraded while consuming oxygen and deliver significantly more energy than anaerobic glycolysis.
It is significant that the body's fat reserves can provide energy for significantly longer than the carbohydrate stores, albeit at a lower intensity. If endurance athletes fail to replenish their carbohydrate supplies in between, there can be a significant drop in performance.
Illnesses & ailments
All diseases that impair the breakdown, transport and absorption of fatty acids and glucose have negative consequences for the supply of energy. In diabetes, the primary impairment is the absorption of glucose from the blood into the cells, for which insulin is required. Depending on the degree of severity, this can lead to an insufficient supply in the muscle cells, which reduces performance. The consequence of this absorption disorder is the rise in blood sugar level, a signal for the pancreas to produce even more insulin in order to reduce this excess. In addition to the long-term organ damage caused by changes in the composition of the blood, this process has a direct impact on the possibilities of mobilizing fat and glucose reserves in the liver. The increased presence of insulin promotes the conversion of glucose into its storage form glycogen and the formation of storage fat, which inhibits the mobilization of these substances for energy delivery.
Liver diseases such as fatty liver, hepatitis, liver fibrosis or liver cirrhosis have similar effects on fat mobilization, even if the mechanisms of action are different. The balance between fat absorption and storage on the one hand and breakdown and transport on the other hand is disturbed in these diseases due to enzymatic defects, with effects on overall performance.
There are some rare diseases that take place directly in the muscle cells and in some cases have significant consequences for the people affected. These genetic diseases are summarized under the term metabolic myopathies. There are 3 basic forms with different variants: In mitochondral diseases, the genetic defects cause disturbances in the respiratory chain, which is important for the aerobic breakdown of glucose. This means that either no or only a small amount of ATP is formed and made available as an energy source. In addition to the muscular symptoms, neural degenerations are in the foreground. In the case of glycogen storage disease (the best-known form is Pompe disease), the genetic defects disrupt the conversion of glycogen into glucose. The earlier this disease occurs, the worse the prognosis. The lipid storage disease behaves similarly, but there are problems with fat conversion.
A variety of symptoms occur with all diseases. In the muscles, there are sometimes considerable reductions in performance, rapid fatigue, the occurrence of muscle cramps, muscle hypotonia and, with prolonged progression, muscle wasting.
