The Muscular System : Part 3

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 17 of 27)

Classes of Levers found in the Body. - Practically all of the levers of the body belong either to the first class or the third class. In both of these the muscle power can be applied to the short arm of the lever, thereby moving the body weight through a longer distance than the muscle contracts. In the levers of the second class, however, the weight occupies this position, being situated between the power and fulcrum. The weight, therefore, cannot move farther than the power in this lever. It must always move a shorter distance. While such a lever is of great advantage in lifting heavy weights outside of the body, it cannot be used for increasing the motion of the muscles. For this reason no well-defined levers of the second class are present in the body.

Loss of Muscular Force. - Using a small spring balance for measuring the power, a light stick for a lever, and a small piece of metal for a weight, and arranging these to represent some lever of the body (as the forearm), it is easily shown that the gain in motion causes a corresponding loss in muscular power. If, for example, the balance is attached two inches from the fulcrum and the weight twelve inches, the pull on the balance is found to be six times greater than the weight that is being lifted. If other positions are tried, it is found that the power exerted in each case is as many times greater than the weight as the weight-arm is times longer than the power-arm.

Applying this principle to the levers of the body, it is seen that the gain in motion is at the expense of muscular force, or, as we say, muscular force is exchanged for motion. This exchange is greatly to the advantage of the body; for while the ability to lift heavy weights is important, the ability to move portions of the body rapidly and through long distances is much more to be desired.

Important Muscles. - There are about five hundred separate muscles in the body. These vary in size, shape, and plan of attachment, to suit their special work. Some of those that are prominent enough to be felt at the surface are as follows:

Of the head: The temporal, in the temple, and the masseter, in the cheek. These muscles are attached to the lower jaw and are the chief muscles of mastication.

Of the neck: The sterno-mastoids, which pass between the mastoid processes, back of the ears, and the upper end of the sternum. They assist in turning the head and may be felt at the sides of the neck.

Of the upper arm: The biceps on the front side, the triceps behind, and the deltoid at the upper part of the arm beyond the projection of the shoulder.

Of the forearm: The flexors of the fingers, on the front side, and the extensors of the fingers, on the back of the forearm.

Of the hand: The adductor pollicis between the thumb and the palm.

Of the trunk: The pectoralis major, between the upper front part of the thorax and the shoulder; the trapezius, between the back of the shoulders and the spine; the rectus abdominis, passing over the abdomen from above downward; and the erector spine, found in the small of the back.

Of the hips: The glutens maximus, fastened between the lower back part of the hips and the upper part of the femur.

Of the upper part of the leg: The rectum femoris, the large muscle on the front of the leg which connects at the lower end with the kneepan.

Of the lower leg: The tibialis anticus on the front side, exterior to the tibia, and the gastrocnemius, the large muscle in the calf of the leg. This is the largest muscle of the body, and is connected with the heel bone by the tendon of Achilles.

The use of these muscles is, in most instances, easily determined by observing the results of their contraction.

Hygiene of the Muscles

The hygiene of the muscles is almost expressed by the one word exercise. It is a matter of everyday knowledge that the muscles are developed and strengthened by use, and that they become weak, soft, and flabby by disuse. The effects of exercise are, however, not limited to the large muscles attached to the skeleton, but are apparent also upon the involuntary muscles, whose work is so closely related to the vital processes. While it is true that exercise cannot be applied directly to the involuntary muscles, it is also true that exercise of the voluntary muscles causes a greater activity on the part of those that are involuntary and is indirectly a means of exercising them.

Exercise and Health. - In addition to its effects upon the muscles themselves, exercise is recognized as one of the most fundamental factors in the preservation of the health. Practically every process of the body is stimulated and the body as a whole invigorated by exercise properly taken. On the other hand, a lack of exercise has an effect upon the entire body somewhat similar to that observed upon a single muscle. It becomes weak, lacks energy, and in many instances actually loses weight when exercise is omitted. This shows exercise to supply an actual need and to be in harmony with the nature and plan of the body.

How Exercise benefits the Body. - In accounting for the healthful effects of exercise, it must be borne in mind that the body is essentially a motion-producing structure. Furthermore, its plan is such that the movements of its different parts aid indirectly the vital processes. The student will recall instances of such aid, as, for example, the assistance rendered by muscular contractions in the circulation of the blood and lymph, due to the valves in veins and lymph vessels, and the assistance rendered by abdominal movements in the propulsion of materials through the food canal. A fact not as yet brought out, however, is that exercise stimulates nutritive changes in the cells, thereby imparting to them new vigor and vitality. While this effect of exercise cannot be fully accounted for, two conditions that undoubtedly influence it are the following:

1. Exercise causes the blood to circulate more rapidly.

2. Exercise increases the movement of the lymph through the lymph vessels.

D.C. Heath and Co. - Publishers
Original copyright 1909