yogabook / movement physiology / connective tissue

This applies in particular to bradytrophic tissue. The load deformation curve of the connective tissue is quite flat at the beginning, i.e. a small load is followed by a significant lengthening, but this only applies to a small area known as the foot area, after which there is an essentially proportional elongation.The turnover of various tissues:
ground substance 2 to 9 days,
fibres 300 to 500 days,
skin 5 to 10 days,
synovia, 14 to 21 days,
capsule and ligaments 300 to 500 days,
cartilage 300 years,
intervertebral disc 60 years,
bone 10 years.
The
turnover is not only dependent on the specific tissue, but also on the context in the body, i.e. a cartilage cell of the ankle joint has a higher turnover than a cartilage cell of the knee joint. If the cartilage cell of the ankle joint is removed, it does not retain the fast turnover. The turnover is related to the blood flow in the tissue and also to the temperature of the tissue. The cells of the connective tissue maintain contact with the outside world, i.e. with other components of the connective tissue, through integrins whose extensions penetrate the cell wall. The number and structure of integrins is dependent on the load on the cell, which means that it, and through it the entire tissue, is capable of adaptation. Connective tissue cells produce their own environment in terms of quantity and quality. Due to their high water content, connective tissues have a very low compressibility, but an elasticity that is due to the negative charge of the glucosamine glycans, which partially converge when deformed. This brings chondroitin sulphate chains with the same charge closer together, which stores elastic energy because they want to move away from each other again due to the same charge. The cells in the connective tissue can react to these physical stimuli and the resulting charge shifts and increase their synthesis activity. The flow of electrically charged fluids, i.e. fluid shifts, for example in cartilage or the intervertebral disc, can also lead to an increase in the synthesis activity of the cell. The integrins act as transducers of external stimuli. External mechanical stimuli can thus be converted into internal chemical signals that cause the cell to become active. Mechanical variables such as tension or pressure, frequency, amplitude and intensity are relevant here. This mechanism forms the basis of the trainability of connective tissue. The endoplasmic reticulum produces various matrix molecules that are transported out of the cell by vesicle transport to be incorporated into the matrix in accordance with the signals transmitted inwards by the external stimuli via the integrins. Two extracellular signals have a dampening effect on the productive activity of the cell: the concentration of extracellular matrix molecules and an absent or subliminal stress stimulus. Immobilisation leads to a lack of stimulating stimuli and thus to a decrease in matrix synthesis. The constant remodelling processes in terms of turnover reduce the quantity of fibres and molecules and also their quality in terms of physiological alignment. For tissue with both fast and slow turnover, degradation is generally faster than build-up. Immobilisation damage can amount to 30% or more of the tissue. Using the example of a meniscus suture, Eckstein demonstrated a 38% muscle atrophy in relation to the cross-section and a 14% reduction in the thickness of the cartilage. While the muscle atrophy was compensated after 18 months, the cartilage thickness was still reduced. It follows that the fonts of immobilisation must not be underestimated and that necessary immobilisations must be kept as short as possible.

For all tissues and their respective turnover, it can be stated that the degradation as a result of immobilisation is always faster and more pronounced than the reconstruction, even through targeted training. While tissue degradation through immobilisation is usually 30% depending on the duration, the rehabilitative reconstruction will be between 3 and 20%. The muscle atrophy resulting from a meniscus suture and the subsequent immobilisation is around 38%, the cartilage decreases in thickness by around 14%. The muscle atrophy can be fully recovered within 18 months, but the loss of cartilage thickness cannot. When stretching connective tissue, the shape of the collagen fibres is smoothed with relatively little effort at the beginning. With these small changes in length, which are completely reversible, an elastic stretching of the collagen fibres takes place. In this area, the tissue does not immediately return to its original state, but a stretch residue remains. This effect is known as hysteresis. If this elongation residue returns, this is referred to as viscoelastic deformation, if it remains, or a proportion of it remains, this is referred to as plastic deformation. This generates heat. The viscoelastic tissues of the body should be able to store energy in deformation and convert a large proportion back into kinetic energy, i.e. it is desirable to minimise the residual strain. Energy is stored in connective tissue, particularly when the extremities are reversed in cyclical movements. If a significant force, which is in a range that does not yet cause damage to the connective tissue, acts on a connective tissue evenly over a longer period of time, the tissue deforms, first faster and then slower and slower until a limit value is reached. This levelling out of the deformation is known as creep. As several parameters are involved in this process, the time it takes to reach the limit value cannot be specified uniformly. Conversely, it can be said that when a tissue is stretched to a certain extent, the force required to do so decreases over time. This effect is known as stress relaxation.