"Musculature, Stretching, and Flexibility"
Information compiled by Mr. Paul Riley: Naginata Shugyo; Aurora, CO
Note: The following material has been compiled and presented without markers and footnotes. A material source can be found at the end of the section.
Know your body, Know your limitations, Then dare to stretch your horizons.......
When muscles cause a limb to move through the joint's range of motion, they usually act in the following cooperating groups:
Muscle tissue, which comprises about 40% of human body weight, consists of threads, or muscle fibers, supported by connective tissue. All living cells can move to some degree, but this ability is highly developed in muscles, which act by fiber contraction: the fibers can shorten to two-thirds of their resting length. Muscles vary greatly in structure and function in different organs and animals. Based on structure there are two types of muscles: smooth and striated. "Involuntary," or smooth, muscles are found in the walls of all the hollow organs and tubes of the body (for example, blood vessels and intestines). These react slowly to stimuli from the autonomic nervous system. The "voluntary," or striated, muscles of the body mostly attach to the bones to move the skeleton, and under the microscope their fibers have a cross-striped appearance. Striated muscle is capable of fast contractions. The heart wall is made up of special muscle fibers (cardiac muscle), a type of striated muscle. Some invertebrates have only smooth muscles, and all arthropods have only striated muscles.
STRUCTURE AND FUNCTION
All muscles have basically the same structure, from the tiny stapedius that moves and steadies a little bone (the stapes) in the middle ear to the huge quadriceps femoris located in the front of the thigh. Each muscle has an attachment at both ends, called the origin and the insertion, and a fleshy contractile part, known as the muscle belly. Origins and insertions are usually noncontractile tendons; however, a great variety of muscle architecture is found that obtains the special mechanical advantages required at specific JOINTS. For example, many muscles in the limbs have a pennate architecture (bundles of muscle fibers arranged like the barbs of a feather and springing from the edges of a tendon). This form greatly increases muscular force, but it reduces the distance through which the insertion may be pulled. Having many bundles of fibers in the muscle belly gives greater strength; longer bundles give a greater range of motion.
The nerve control of the muscle fibers is organized in an economical fashion. Each motor nerve fiber running in a motor nerve to a muscle supplies a group of muscle fibers, which twitch each time an impulse is sent down the nerve fiber from the spinal cord. The frequency of these twitches can be increased and the number of motor units involved can be increased until all units are twitching rapidly (up to 50 times per second). The blending of all the twitches results in a smooth contraction of the entire muscle. If the twitches fail to blend well but instead come in bursts, an obvious tremor results. Tetanus occurs when the frequency of pulses is such that the fibers remain tense continuously.
A muscle produces movements of a joint and can only act on the joints it crosses; muscles also steady joints, preventing movements in the direction opposite to those intended. For instance, the triceps brachii, which makes up the muscle mass on the back of the arm, not only is a powerful extensor straightener of the elbow joint; it also contracts strongly to prevent the elbow from bending when pushing with the hand. In many muscles of the lower limb it is gravity that must be counteracted; for example, the muscles are just as important to keep a person erect as they are in raising the heels off the ground.
The optimum angle of pull of a muscle is achieved when the muscle is acting more or less across a right angle of a joint; however, muscles are usually working across angles that are necessarily less advantageous. The inefficiency is only of a mechanical nature, though, because the extra heat energy generated helps warm-blooded animals maintain their temperature for optimum functioning of the body.
In mechanical terms, the skeleton provides leverage, the muscles are the motors that act on the levers, and the joints provide fulcrum. The body employs all the typical leverage forms known to engineers. Most levers in the human body are levers of the first class; these are exemplified by the familiar see-saw and the crow-bar. Levers of the third class are also common in the body; the ordinary hinged door is an example, the handle being the point at which the force is applied. In the body, this force is exerted by a tendon attached to a bone; almost always the tendon is attached near a hinge in order to provide proper mechanical advantage.
The brain needs to be specifically trained in order to contract individual muscles. Animals, including human beings, "will" movements of joints and limbs. Individuals do not consider the amount of contraction necessary in biceps brachii, brachialis, and brachioradialis muscles to develop the force and speed required to move an elbow. Voluntary movement takes learning, perhaps over many months and years, and it becomes automatic or semiautomatic, reaching its finest expression in the virtuoso performance of a great musician or a champion athlete. All human movements and postures, with the exception of a few primitive, life-sustaining reflexes, are learned and patterned by repetition. Another major factor is the coordination of muscle actions, which is learned, and which depends on the cerebellum and brain stem for a form of subconscious training. Muscles often must be trained to work as teams, both dimensionally and sequentially.
Training not only improves coordination; it also makes muscles stronger. This occurs because individual muscle fibers become thicker and more powerful; they do not, however, increase in number. Each creature is born with its full quota of fibers. Normal growth and the increase in volume that comes from exercise depend on enlarging this set number of fibers. Conversely, a muscle atrophies (shrinks and weakens) when it is not used or has had its nerve supply cut. If the nerve supply remains intact or is restored, exercise will bring the muscle back to its former condition.
In the next installment I will continue with Classification, Supplementary Structures, and Major Muscles and Muscle Groups.
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