Muscles are made up of fibers that can contract under the influence of nerve impulses. They are an active element of the musculoskeletal system, as they provide a variety of movements when moving a person in space, maintaining equilibrium, respiratory movements, contracting the walls of internal organs, voice formation and so on.
There are three types of muscle tissue: skeletal, smooth, and cardiac. The function of heart tissue is clear from the name. Smooth muscles are the muscles of internal organs. They reduce the walls of blood vessels, produce a reduction in the intestines, facilitating the movement of food, and perform many other vital functions. We cannot control these two types of muscles, only reflexes work here. Skeletal muscles are exactly what you want to pump with iron. The function of skeletal muscles is the movement of parts of the skeleton relative to each other. It is about these muscles that we will talk further.
Skeletal muscle consists of striated muscle fibers connected by loose connective tissue into bundles of the first order. They, in turn, are combined into second-order bundles and so on. As a result, muscle bundles of all orders are combined by the connective membrane and form the muscle “abdomen”. The connective tissue layers, which are located between the muscle bundles along the edges of the “abdomen”, pass into the tendon part of the muscle attached to the bone. During contraction, the muscle “abdomen” is shortened and its edges come closer. At the same time, the contracted muscle with the help of a tendon pulls a bone behind it, which plays the role of a lever. This is a somewhat simplified model of motion.
The muscles are equipped with blood vessels and nerve endings. Each movement involves several muscles. Those muscles that act together in the same direction and cause a similar effect are called synergists, and those who perform oppositely directed movements are called antagonists.
To make it clearer, I will explain with an example. The flexor of the elbow joint is the biceps muscle of the shoulder (the more common name is biceps), and the extensor is the triceps (respectively, triceps). When the flexor muscles of the elbow joint contract, the extensor muscles, on the contrary, relax. But with a constant load on the joint (for example, when holding the dumbbell in a horizontally extended arm), the muscles – flexors and extensors of the elbow joint no longer act as antagonists, but as synergists, holding the hand in this position. So muscle action cannot be reduced to performing only one function. They are multifunctional.
Thus, according to the nature of the movements performed, the following types of muscles are distinguished: flexors and extensors, leading and abducting, rotating, lifting and lowering, etc. Mimic, chewing and respiratory muscles are also distinguished.
In the figures you can see where which muscles are located to have an idea of what and how to pump!
Fig. 1. The muscles of the frontal surface of the body:
1 – styloid process of the radius; 2 – ligament of the triceps muscle; 3 – intermuscular septum; 4 – pectoralis major muscle; 5 – clavicular part; 6 – sternum; 7 – a large round muscle; 8 – latissimus dorsi; 9 – anterior dentate muscle; 10 – oblique external muscle of the abdomen; 11 – rectus abdominis muscle; 12 – aponeurosis; 13 – muscle straining the wide fascia of the thigh; 14 – the rectus femoris muscle; 15 – lateral thigh muscle; 16 – middle muscle of the thigh; 17 – a long fibular muscle; 18 – calf muscle; 19 – anterior tibial muscle; 20 – long extensor of the fingers; 21 – soleus muscle; 22 – front retainer of the tendons of the extensor muscles; 23 – lateral ankle; 24 – the middle ankle; 25 – Achilles tendon; 26 – long flexor of the toes; 27 – tibia; 28 – semi-membranous muscle; 29 – tendon expansion; 30 – patella; 31 – knee ligament; 32 – tender muscle; 33 – long adductor muscle of the thigh; 34 – tailor muscle; 35 – scallop muscle; 36 – iliopsoas muscle; 37 – inguinal ligament; 38 – anterior spine of the ilium; 39 – white line of the abdomen; 40 – border of the ribs; 41 – sternal line; 42 – beak shoulder muscle; 43 – a long head; 44 – triceps muscle of the shoulder; 45 – brachial muscle; 46 – round pronator; 47 – ulnar process; 48 – beam flexor of the bone; 49 – ulnar flexor of the bone; 50 – long extensor of the fingers; 51 – short head
The universal source of energy in a living organism is the ATP molecule. Under the action of a special enzyme (ATPase), ATP is hydrolyzed and converted to ADP, and energy is released, which is used to reduce muscle fibers. But the initial supply of ATP molecules in the muscle is limited, therefore, when the muscle is working, constant replenishment of energy reserves is required (i.e., ATP resynthesis).
The muscle has three sources of energy reproduction: the breakdown of creatine phosphate, glycolysis, and oxygen oxidation.
Muscles of the back of the body:
1 – upper trapezius muscle; 2 – the average trapezius muscle; 3 – deltoid muscle; 4 – lower trapezius muscle; 5 – a long head of triceps; 6 – the middle head of the triceps; 7 – biceps muscle of the shoulder; 8 – brachial muscle; 9 – round pronator; 10 – beam flexor of the bone; 11 – a long palmar muscle; 12 – long abduction muscle of the thumb; 13 – brachioradialis muscle; 14 – a large adducting muscle of the thigh; 15 – a long head of the biceps femoris; 16 – short head of the biceps femoris; 17 – tender muscle; 18 – semitendinosus muscle; 19 – semi-membranous muscle; 20 – tailor muscle; 21 – the middle head of the calf muscle; 22 – knee ligament; 23 – tibia; 24, 26 – soleus muscle; 25 – long extensor of the toes; 27 – short fibular muscle; 28 – a long fibular muscle; 29 – a long flexor of the toes of the foot; 30 – anterior tibial muscle; 31 – lateral head of the calf muscle; 32 – head of the fibula; 33 – knee ligament; 34 – biceps femoris muscle; 35 – lateral broad muscle of the thigh; 36 – rectus femoris muscle; 37 – muscle straining the broad fissure of the thigh; 38 – gluteus maximus muscle; 39 – oblique external muscle of the abdomen; 40 – anterior dentate muscle; 41 – periosteal muscle; 42 – latissimus dorsi; 43 – a large round muscle; 44 – a small round muscle; 45 – side head triceps; 46 – brachial muscle; 47 – biceps muscle of the shoulder; 48 – ulnar extensor brush; 49 – short beam extensor of the hand; 50 – common extensor of the fingers; 51 – long abduction muscle of the thumb; 52 – long radial extensor of the bone; 53 – brachioradialis muscle
This reaction is called the Loman reaction. The reserves of creatine phosphate in the fiber are small, so it is used as an energy source only at the initial stage of muscle work – in the first few seconds.
After creatine phosphate reserves are depleted by about 1/3, the rate of this reaction will begin to decrease, and this will trigger the inclusion of other ATP resynthesis processes – glycolysis and oxygen oxidation. At the end of the work of the muscle, the Loman reaction goes in the opposite direction, and the reserves of creatine phosphate are restored within a few minutes.
The breakdown of creatine phosphate plays a major role in the energy supply of short-term exercises of maximum power – short-distance running, jumping, throwing, weightlifting and strength exercises – lasting up to 20s.