Muscle, ligament, tendon, joint capsules, meniscus and cartilage belong to the category of the soft tissues. Bone tissue belongs here as well, even though it may seem that bone appears as a sufficiently hard mass. The reason is its ability to change its properties, density or shape thanks to the physical forces, which constantly affect it.
EFFECTS OF PHYSICAL FORCES ON THE DEVELOPMENT AND GROWTH OF THE TISSUES
All the tissues react to the external impacts. For example, if the muscles of an athlete are excessively burdened, there will be an increase of the motor units, increased number of muscle fibres which will also start to grow in both, width and length. Such muscles then affects the tendons, which are also strengthened, and its transitions are also strengthened (transitions from tendon to muscle and tendon to bone). The most fragile transition, prone to damage is the tendon/bone transition, since significantly softer tissue (tendon) is transitioning to significantly harder tissue (bone). Therefore these ruptured tendons are frequently occurring in the areas where they are attached to the bone, due to being most “fragile” in these area.
Athletes tend to have rougher surface structure of the bones, than people who don’t sport that much, and at the same time the rougher bone surface can be observed in men than by women. The shape of the bones is changing according to the effects of pressure, which is involved on them for a long period of time.
If the effect of physical forces is balanced, and the soft tissues are affected evenly stimulated the tissues will have enough space and time for possible regeneration, then everything is alright and the development is considered to be physiological.
If the number of stimulations and intensity is insufficient, it will lead to insufficient development, alternatively it can result in atrophy of the tendons, ligaments, muscles, and by bones we talk about osteoporosis.
On the other hand, if the amount of physical forces in form of pressure or vibrations affect the soft tissues especially if they are dominated above the ability of regeneration and adjustment of the tissue to the physical factors, it leads to degeneration of the tissue and even to its damage. For example during insufficient production of synovial fluids in the joints can lead to draining of the cartilage, cracking and formation of the arthrosis with gradual decrease of the cartilage tissue in the joint area. Joint capsule, ligament, tendon and muscle can under increased pressure tear apart which can also break the bone beneath. It is not an exception, that untrained people or people who train too much can be disabled by a stress fracture. For example, by runners we observe stress fractures of the tibial or heel bone.
Typical example of changed bone shape can be:
- Head of the femur bone (thigh bone), if it is not centered in the joint socket of the pelvic bone, it can be dulled, and the angle between the femur head and the thigh bone is closed.
- If the pressure around the spine on the right side is higher, it will lead to gradual decrease height of the body of the vertebra on the right. On the other hand, the side with lower muscle tension on the left side can be observed by increased height on the left side of the vertebral body than on the right side, that is how scoliosis forms.
CHANGED DENSITY OF THE BONES
Long lasting affecting of the physical forces (pressure, traction) on the bone can be considered to be cca 3 months. For example osteoporosis forms not only as a result of hormonal changes by women after menopause. We can observe it there most frequently, but it forms also in time when the bone is not sufficiently exercised during long lasting illness, when we are constantly lying in bed, the bone is not burdened with pressure and traction during walking, sitting, etc.
It leads to decalcification and atrophy (disappearance) of the muscle tissue, which we observe as a first result of inability to move. The fracture of small bones in the instep is thanks to insufficient blood supply and nutrition also leads to atrophy of the bones.
THE EFFECT OF GRAVITY ON THE FUNCTION OF MUSCLE AND BONES
The astronauts are before the mission to space very well trained not only in centrifuges, and other devices, so that they could deal with the pressure, but also simple physical activities (running, weight lifting, dynamic exercising,...). Their goal is to increase the muscle mass and strengthen their musculoskeletal apparatus. Outside the earth they won’t be exposed to the gravitational force of the earth, and therefore they are exposed to slow degenerative process of their bones, muscles and tendons - decalcification of the bones and starting atrophy in the musculoskeletal muscles, but also cardiac muscle and vascular smooth muscles are degenerating.
Astronauts who are spending longer time on the orbit, have to spend 2 hours a day exercising on devices which they have available on their station. Anaerobic exercise is part of their working duty. Regular trainings at least partly keeps their musculoskeletal mass and density of the bones, but also their heart has to be regularly “exercised”. In case the astronauts would not intensively exercise before the launch and during their stay in space, the return to earth would be fatal for them afterwards. The muscles after the return could not deal with the gravitational pull of the earth, that goes for heart as well, and muscles of the vascular smooth muscles in the blood bloodstream, whose primary task is to distribute the oxygenated blood and nutrients to brain, lungs and absolutely vital organs. Bones would get during the flight fragile (osteoporosis) and either during the return they would not be able to deal with the overload, or they would not be able to deal with the gravitational pull of the earth, and compression fractures of the vertebrae and longer bones would occur.
Author: Mgr. Iva Bílková, FYZIOklinika fyzioterapie Ltd, Prague, Czech Republic