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The physiology of muscular contraction
The skeletal muscle performs its functions through contraction. Muscle
contraction causes joint movement and therefore skeleton movement.
Muscle contraction takes place as follows: when a person decides to
make a movement, the electric potential in the brain motor center is
changed and an electric signal is sent to the muscle that will have to
contract.
The electric signal is sent as a potential (voltage) change and an electric
pulse passes through the motor nerve to the muscle that has to be
stimulated.
After the pulse is received, Ca ions are released causing actin-myosin
rapprochement. As a result, the distance between Z bands decreases
causing muscle contraction
The necessary energy is provided by sugar and fat reserves of the human
body. In other words, electric stimulation is not a direct source of energy,
but acts as a tool that triggers muscle contraction.
The same mechanism is activated when muscle contraction is produced
by EMS. In other words, they act as a natural pulse sent by the motor
nervous system.
The muscle usually relaxes and goes back to its original state at the end
of the contraction.
Isotonic and isometric contraction
Isotonic contraction occurs when, in a body movement, muscles produce
a state of constant tension. On the other hand, when the articular ends
of a body part are blocked, muscles produce a tension that is called
isometric contraction.
In the case of electrostimulation, isometric contraction is preferred as it
can be controlled more effectively.
The distribution of the different fiber types in the muscle
The relationship between the two main categories (type I and type II)
can vary in a considerable way. There are muscular groups that are
typically made up of type I fibers, like the soleus, and muscles that only
have type II fibers, like the orbicular muscle; however, the majority of
human body muscles is composed of a combination of the two types.
Studies on the distribution of fibers in the muscle have highlighted the
close relationship between the (tonic or phasic) motoneuron and the
functional features of the fibers it innervates; moreover, they have
proved that a specific motor action (particularly in sports) can lead to
a functional adaptation of fibers and change their metabolic features.
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Rev. 03 Multi_06_2018
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