How Does Muscle Building Work? A Journey into the World of the Muscle.
How does muscle building work?
So how does muscle building really work? Again and again you hear myths, such as that muscles grow in spurts. In today's blog we therefore look at the structure of the muscle as well as the biological processes involved in building muscle.
Structure of the muscle
The muscle consists of so-called muscle fibre bundles. The muscle fibre bundles are the visible meat "fibres" you can see with the naked eye and have a diameter of approx. 100 - 1000 μm. The muscle fibre bundles in turn consist of several muscle fibres. The muscle fibres are muscle cells with a diameter of approx. 10-100 μm (10-100·10-6 m) and can be several centimetres long. The cell membrane of the muscle cell is called the sarcolemma and encloses the sarcoplasm (cytoplasm), several cell nuclei, mitochondria, substances for the supply of oxygen and energy, and a few hundred myofibrils.
Each myofibril within the muscle fibre is divided by so-called Z-discs into compartments approx. 2 μm long, called sarcomeres. The (half-)sarcomere is the smallest contractile unit of the muscle. Under (two-dimensional) microscopic observation, the myofibrils show alternating light and dark bands and lines (hence cross-striated muscle), which are caused by the arrangement of the (thick) myosin-II and (thin) actin filaments. A sarcomere lies between two Z-lines or, three-dimensionally, between Z-discs (picture below).
a) Schematic representation of the main components of a sarcomere (Pradeep K. Luther 2009)
b) View of a sarcomere based on an electron microscope longitudinal section of a fish muscle (Pradeep K. Luther 2009)
Filament sliding
Muscle contraction occurs through filament sliding, with energy in the form of adenosine triphosphate (ATP). The myosin heads, with their ATPase activity, are the motors. The actin and myosin filaments of a sarcomere are thus arranged so that they can slide into each other. The myosin heads connect to the actin filaments at a certain angle. Through a conformational change in the binding area, whose spatial extent is increased by movement of the neck region, the head of the myosin "bends" and pulls the thin filament over 4 nm (4 · 10-9 m) with it. The head then releases, is "cocked" again, and after rebinding to actin makes the next "rowing stroke".
How does muscle building work?
Muscle building is about forming muscle proteins. This happens via the so-called muscle protein synthesis rate. Opposed to this is the muscle protein breakdown rate. If the muscle protein synthesis rate is now greater than the muscle protein breakdown rate, more muscle protein is produced and the muscle "grows".
Muscle protein synthesis
Protein synthesis, greatly simplified, works as follows. The cell nuclei contain the DNA. DNA is a very long molecule which in humans exists as chromosomes. It contains the encoded genetic blueprint of all cells in the living organism. However, the production of proteins does not take place in the cell nucleus but outside it. Since the DNA cannot leave the cell nucleus, its information must be copied. The information is copied from the DNA onto so-called RNA. This process is called transcription. A section of DNA that is "written" onto an RNA for a hereditary trait is called a gene.
The mRNA (messenger RNA) is transported through the nuclear pores into the cytoplasm. In the cytoplasm it binds to ribosomes. The ribosomes translate the information into the amino acid sequence of the protein. This is also called translation. The amino acids for making muscle proteins come from amino acids released when other proteins are broken down, or from protein taken in through food. Muscle proteins are therefore built up and broken down at all times. Right now, too, you are building up and breaking down muscle protein.
A muscle cell can regulate both transcription and translation. This happens, for example, through training and nutritional stimuli.
