Growth stimulus
The growth stimulus is the threshold from which a change in the direction of increased mass ( hypertrophy ) occurs in the muscle substance.
A stimulus that is effective for growth or training signals to the body that the current body's own strength resources are not sufficient to cope with the given loads. The body reacts to this with supercompensation , which means that it increases its capacity to deal with the load, in this case by increasing the muscle cross-section.
background
A muscle is made up of many individual muscle fibers that contract to create force. The nervous system always addresses as many fibers as are necessary to exert the required force, of course restricted by biological aspects such as maximum strength and intramuscular coordination ; It is currently (2008) assumed that a maximum of 30% of all muscle fibers are activated at the same time. After the fibers addressed first are tired, the next ones are addressed, and so on. Once all the fibers present have been addressed, the cycle starts all over again. With little stress and good training condition, this cycle could theoretically continue indefinitely without creating any growth stimulus. If the load is sufficiently high in relation to the level of training, this cycle comes to an end when the muscle relaxes or fails. In the last moments before the so-called reserve fibers are addressed, i. H. Muscle fibers that are naturally present, but have a comparatively small amount of high-energy substance and are accordingly thinner than the active muscle fibers. This activation leads to the conversion of these reserve fibers into active fibers, which causes the growth of the muscle cross-section described above.
Restriction
The growth stimulus can be set again and again for a surprisingly long time, but it cannot be increased indefinitely. It is limited, among other things, by the genetically created number of reserve fibers.