Skeletal muscle work is controlled by the human mind, i.e. submits his desires (arbitrarily). Two processes are carried out at the same time upon exc

Skeletal muscles work

Skeletal muscle work is controlled by the human mind, i.e. submits his desires (arbitrarily). Two processes are carried out at the same time upon excitation of the muscles — contraction and tension (diagram 37). Usually, one of them prevails, and that determines the different modes of muscular work.

The muscles work that allows to move the cargo as a result of movements of the bones in the joints, called dynamic. Static work — this is when the muscles tense, but does not get shortened.

Contraction force is measured in kilograms per square centimeter of cross-sectional muscle. For a calf, it is 5.9 kg/cm2 for the biceps shoulder — 11.4 kg/cm2.

Diagram 37. Muscles work: a) flexor work (1) and extensor (2). The blue arrows indicate relaxation, red — muscle contraction. When the motor centers of the brain (3), the cerebellum (4) and spinal cord (5) send a signal for the flexor to contract (green), at the same time the extensors relax (gray) and the arm is bent at the elbow; b) forces diagram: F1 — force of muscle contraction; F2 — the force of attraction of the subject

The muscle work is measured by multiplying the mass of raised cargo and the height it was raised. It will be zero when muscle contracts with no load or when the load is too heavy and lift height equals zero.

A muscle performs the hardest work at average loads and average rhythm of contractions.

The power of skeletal muscles is the work done per unit of time. It will be maximum be at medium loads. Indicator of muscle performance — is a coefficient of efficiency. Skeletal muscle has 25-30%: this is the part of the energy that is consumed for the muscle contraction. The remaining 70-75% of the energy is converted into heat. Taken from http://worldofschool.org

Muscle acts like the lever on bones, connected by joint (diagram 37). To carry out various precious and often the opposite directed movements, the skeletal muscles are arranged the way that one muscle action contrasts the actions of the other. Contracting, muscle causes the movement of a certain part of the body, and when the opposing muscle starts to work, it returns to its original position. These muscles are called antagonists. Examples of these are flexors, that flex limb in the joint, and extensors that straighten it. If they contracts simultaneously, the limb is straightened.

In human body there are muscle-synergists (Greek: those that act together), which operate in the same direction. Usually, complex movements affect both antagonists, and synergists.

Categories:
Questions:
  • Explain the definition of "tonus", "work", "force contraction" and "muscle power".

  • Determine the importance of the static and dynamic muscle work.

  • How does different muscle groups coordinate?