Major Muscles and muslce power

Since muscle fibers exert pull when they contract, they use energy. The energy comes from food supplied to them through the blood. A muscle works by converting chemical energy into mechanical energy. Actually, only about one fourth of the chemical energy is converted properly into mechanical energy; the remaining three fourths is lost as heat, raising the temperature of anyone doing strenuous work. This efficiency of 25 percent is similar to that of an automobile engine, which also loses much of its energy as heat. There have been calculations which suggest that the maximum energy output for man is about 6 horsepower and that as much as 0.5 horse- power output can be sustained almost indefinitely.

SOME MAJOR MUSCLES Skeletal muscles are of many shapes and sizes suited to their particular jobs-and they have many jobs. The sternomastoid muscles, which are on either side of the head, serve two purposes. When you nod your head, it is because both of the sternomastoid muscles contract simultaneously. You turn your head to one side or the other depending upon which of the two you contract. Among muscles at the shoulder are the trapezius, which shrugs the shoulder when it contracts, and the pectoralis major, which spreads over the chest and attaches to the humerus and helps sweep the arm across the chest. On the forearm are muscles that divide into tendons extending down to the fingertips; they help move the fingers.

 Among the big muscles of the lower extremity are the gluteal muscles on the buttocks, which, with their contraction, move you from sitting to standing position and are involved in walking; the sartorius, in the thigh, the longest muscle in the body, which pulls the thigh into cross-legged position; the quadriceps in the thigh used [or balance during standing and for kicking; and the gastrocnemius and solt'us in the calf which enable you to stand on tiptoe and provide from the ground for walking, running, dancing. Along each side of the spinal column maintain an erect posture, to bend the body, and to help turn it to one side or the other. Inside the body is the major muscle for breathing, the diaphragm, which is attached through tendons to the spinal column, ribs, and lower tip of the breastbone. The contraction of the diaphragm helps fill the lungs with air. And the diaphragm, incidentally, is also used in laughing, sneezing, and coughing. Its spasmodic contractions occasionally produce hiccupping. 

TYPES OF MUSCLES Muscle Fibers

TYPES OF MUSCLES 

Each muscle is made up of a bundle of fibers, each of which is about the size of a hair and capable of supporting 1,000 times its own weight. All told, there is something more than 6 trillion fibers in the muscles throughout the body. There are three types of muscle tissue. One, when viewed under a microscope, has dark and light bands across the fibers, and is known as striped muscle. It is also called skeletal muscle because it is attached to some part of the skeleton. And it is classed as voluntary muscle because it is under the control of the conscious part of the brain. This is the type of muscle used to walk, write, lift, and throw to perform any movement we actually will to be done.

A second type of muscle, called smooth or involuntary, lacks the dark and light bands. This type of muscle handles the functions of all internal organs except the heart. It is involved in the vital movements of the stomach and intestine, for example. It is called involuntary since we do not have direct control over its action. Its workings are automatic, freeing us from concern over it, allowing us opportunity to concentrate on other matters. The third type of muscle that of the heart is called cardiac. It is striped like the voluntary type but has no sheaths as the voluntary does. It, too, is involuntary.

Muscle fibers vary considerably in length, from as little as 0.04 inch or even less to 1.5 inch or more. The diameter, of course, is very small, as little as 0.004 inch or even less. When a muscle contracts, it becomes shorter by as much as one third to one half, and as it shortens, it thickens. Most skeletal muscles are linked to a bone either at one end or at both ends. The tendons, or sinews, which do the linking, vary considerably in size, ranging up to more than a foot in length. Ligaments, like the tendons, are made up of strong fibrous tissue, but their function is to bind bones together. Tendons join muscle to bone; ligaments join bone to bone. Ligament fibers stretch. Tendons are so strong that a bone may break before the tendon attached to it gives way. When muscles join bones, one of the bones usually functions as an anchor to help move the other bone.

The point where the muscle attaches to the anchor bone is known as the point of origin. The attachment to the bone that does the moving is called the insertion. Before a muscle can contract, it must receive a contract signal. In the case of voluntary muscles, the signal comes from the brain via the central nervous system and is relayed' instantly through tiny nerves that reach each of the fibers involved. Involuntary muscles get their signals from the autonomic nervous sys- tem, which is concerned with the regulation of body functions that do not have to be under conscious control. To be sure, even in the case of voluntary muscles, you are not required to give a direct order-to take the time to stop and think and issue a command for a particular muscle to contract. You simply decide to bend an elbow, move a finger, throw a ball-and the brain and nervous system translate the decision into orders which go to the proper muscle fibers. 

THE MUSCLES BONES

THE MUSCLES BONES 

FORM the framework; joints permit movement; and it is the muscles that do the moving when they pull on bones. The hundreds of voluntary muscles in the body weigh two and one-half times as much as all the bones together. They constitute the flesh that gives the body its basic shape. An understanding of muscles and how they function is very much worth having, since it can help you to use your muscles most effectively, prevent injuries to them, and prevent progressive deterioration if an injury should occur. As noted in the preceding chapter, good muscle tone is an important element in preventing skeletal problems, and as we will point out in this chapter, tone is also important in maintaining good circulatory function. Muscles always work by pulling, never by pushing.

Muscle fibers contract and as they do so the muscle pulls a bone toward it. The body is so engineered that where one muscle acts to pull a bone in one direction, there is another muscle that can be contracted to pull the bone in the opposite direction. Thus, for example, the bulge that can be felt in the front of the upper arm when the lower arm is drawn up is the body of the biceps muscle. The mate to the biceps, called the triceps, lies on the opposite side of the arm and when this muscle contracts it straightens the elbow and stretches the biceps into position for another contraction.

 Muscle tissue is formed before birth, and a baby's supply of muscle fibers is his supply for life. The fibers, of course, grow as the child grows. Strength develops as the fibers do their work of contracting. The arms of a blacksmith, prizefighter, or weightlifter contain about the same number of fibers as do those of a little girl but are much stronger and thicker through use.