What happens in physical education

Muscle fiber (muscle cell)

Muscle fiber and sarcomere...


 If you put them under a microscope, you can see that the fiber bundles consist of other subunits - the actual muscle cells.

The muscle fibers consist of a large number of so-called (Myo-) fibrils.
The secret of muscle movement lies primarily in these myofibrils. They consist of tiny, lined up chambers, the sarcomeres. When the muscle contracts, two main types of thread-like proteins act in it, myosin and actin. They are long, thin threads made up of two different proteins - actin and myosin.
The actin forms firm attachment discs at regular intervals from which thin threads emanate. The myosin molecules lie between these threads. Their ends overlap with the ends of the actin threads.

Now what happens when the nerves give the order to contract muscles?
The nerves and blood vessels responsible for supplying the muscles run in the connective tissue. The nerves control the movements; by relaying commands from the brain and spinal cord to the muscles. The muscle cells (usually several) are in contact with a nerve ending (synapse) and react to their electrochemical signal by contracting. When we perform complex movements, the work of many millions of muscle cells has to be coordinated in this way.
The myosin molecules grip the actin threads like small barbs and pull them towards each other. This pushes the two proteins into one another like parts of a telescopic antenna. Effect: The muscle fiber shortens and becomes thicker. The thickening of the individual fibers adds up.

But of course the muscle fibers also need "fuel" - because movement is known to cost energy. The blood vessels are responsible for the energy supply. The fuel consists of carbohydrates, fats and proteins. Countless small veins (capillaries) run through the connective tissue sheaths of the muscle fibers, spinning around them with a dense supply network. Lined up in a row, the tiny blood vessels of the human musculature would stretch more than twice around the earth.

The nutrients supplied by the blood contain energy, but this energy is chemically bound and is not directly available to the cells. Just like gasoline in an engine, nutrients must first be burned to produce movement. This happens in special cell organs (mitochondria) that are present in every muscle cell. Because of their function as an energy supplier, theMitochondria also known as the "power plants" of cells.

The energy gained by burning the nutrients is initially stored in a special molecule, theAdenosine triphosphate (ATP). The ATP then migrates from the cell power plants to the myofibrils, the smallest units of the muscle in which the movement is generated. There, the ATP releases the stored energy the moment the muscle contracts: Physical training increases the number of myofibrils and thus the thickness and strength of the muscle. The mitochondria - cell power plants - can also be increased through training and thus improve the energy supply.