We will now look more closely at a muscle fiber, keeping in mind that there are thousands of these cylindrical cells in one muscle. Each muscle fiber has its own motor nerve ending; the neuromuscular junction is where the motor neuron terminates on the muscle fiber. The axon terminal is the enlarged tip of the […]

Before discussing the contraction process itself, let us look first at how muscle fibers obtain the energy they need to contract. The direct source of energy for muscle contraction is ATP. ATP, however, is not stored in large amounts in muscle fibers and is depleted in a few seconds.
The secondary energy sources are creatine phosphate […]

When you walk up a flight of stairs, do you have to look at your feet to be sure each will get to the next step? Most of us don’t (an occasional stumble doesn’t count), and for this freedom we can thank our muscle sense. Muscle sense (proprioception) is the brain’s ability to know where […]

Good muscle tone improves coordination. When muscles are slightly contracted, they can react more rapidly if and when greater exertion is necessary. Muscles with poor tone are usually soft and flabby, but exercise will improve muscle tone.
There are two general types of exercise: isotonic and isometric. In isotonic exercise, muscles contract and bring about movement. […]

Synergistic muscles are those with the same function, or those that work together to perform a particular function. Recall that the biceps brachii flexes the forearm. The brachioradialis, with its origin on the humerus and insertion on the radius, also flexes the forearm. There is even a third flexor of the forearm, the brachialis. You […]

Muscles are arranged around the skeleton so as to bring about a variety of movements. The two general types of arrangements are the opposing antagonists and the cooperative synergists.
Antagonists are opponents, so we use the term antagonistic muscles for muscles that have opposing or opposite functions. The biceps brachii is the muscle on the front […]

All muscle cells are specialized for contraction. When these cells contract, they shorten and pull a bone to produce movement. Each skeletal muscle is made of thousands of individual muscle cells, which also may be called muscle fibers . Depending on the work a muscle is required to do, variable numbers of muscle fibers contract. […]

Do you like to dance? Most of us do, or we may simply enjoy watching good dancers. The grace and coordination involved in dancing result from the interaction of many of the organ systems, but the one you think of first is probably the muscular system.
There are more than 600 muscles in […]

Living cells constantly interact with the blood or tissue fluid around them, taking in some substances and secreting or excreting others. There are several mechanisms of transport that enable cells to move materials into or out of the cell: diffusion, osmosis, facilitated diffusion, active transport, filtration, phagocytosis, and pinocytosis. Some of these take place without […]

Cytoplasm is a watery solution of minerals, gases, organic molecules, and cell organelles that is found between the cell membrane and the nucleus. Cytosol is the water portion of cytoplasm, and many chemical reactions take place within it. Cell organelles are intracellular structures, often bounded by their own membranes, that have specific functions in cellular […]

With the exception of mature red blood cells, all human cells have a nucleus. The nucleus is within the cytoplasm and is bounded by a double-layered nuclear membrane with many pores. It contains one or more nucleoli and the chromosomes of the cell.
A nucleolus is a small sphere made of DNA, RNA, and protein. The […]

Despite their many differences, human cells have several similar structural features: a cell membrane, a nucleus, and cytoplasm and cell organelles. Red blood cells are an exception because they have no nuclei when mature. The cell membrane forms the outer boundary of the cell and surrounds the cytoplasm, organelles, and nucleus.
Also called the plasma membrane, […]

All living organisms are made of cells and cell products. This simple statement, called the cell theory, was first proposed more than 150 years ago. You may think of a theory as a guess or hypothesis, and sometimes this is so. A scientific theory, however, is actually the best explanation of all available evidence. All […]

Nerve tissue consists of nerve cells called neurons and some specialized cells found only in the nervous system. The nervous system has two divisions: the central nervous system (CNS) and the peripheral nervous system (PNS). The brain and spinal cord are the organs of the CNS. They are made of neurons and specialized cells called […]

Muscle tissue is specialized for contraction. When muscle cells contract, they shorten and bring about some type of movement. There are three types of muscle tissue: skeletal, smooth, and cardiac. The movements each can produce have very different purposes.
Skeletal muscle may also be called striated muscle or voluntary muscle. Each name describes a particular aspect […]

There are several kinds of connective tissue, some of which may at first seem more different than alike. The types of connective tissue include areolar, adipose, fibrous, and elastic tissue as well as blood, bone, and cartilage. A characteristic that all connective tissues have in common is the presence of a matrix in addition to […]

Epithelial tissues are found on surfaces as either coverings (outer surfaces) or linings (inner surfaces). Because they have no capillaries of their own, epithelial tissues receive oxygen and nutrients from the blood supply of the connective tissue beneath them. Many epithelial tissues are capable of secretion and may be called glandular epithelium, or more simply, […]

Multiple studies have now shown that people who maintain appropriate body fitness, using judicious regimens of exercise and weight control, have the additional benefit of prolonged life. Especially between the ages of 50 and 70, studies have shown mortality to be three times less in the most fit people than in the least fit. But […]

Without belaboring this issue, let us list some of the effects of drugs in athletics. First, caffeine is believed by some to increase athletic performance. In one experiment on a marathon runner, running time for the marathon was reduced by 7 per cent by judicious use of caffeine in amounts similar to those found in […]

As much as a 5- to 10-pound weight loss has been recorded in athletes in a period of 1 hour during endurance athletic events under hot and humid conditions. Essentially all this weight loss results from loss of sweat. Loss of enough sweat to decrease body weight only 3 per cent can significantly diminish a […]

Almost all the energy released by the body’s metabolism of nutrients is eventually converted into body heat. This applies even to the energy that causes muscle contraction for the following reasons: First, the maximal efficiency for conversion of nutrient energy into muscle work, even under the best of conditions, is only […]

Muscle Blood Flow. A key requirement of cardiovascular function in exercise is to deliver the required oxygen and other nutrients to the exercising muscles. For this purpose, the muscle blood flow increases drastically during exercise. A recording of muscle blood flow in the calf of a person for a period of […]

Oxygen Consumption and Pulmonary Ventilation in Exercise. Although one’s respiratory ability is of relatively little concern in the performance of sprint types of athletics, it is critical for maximal performance in endurance athletics. Normal oxygen consumption for a young man at rest is about 250 ml/min. However, under maximal conditions, this can be increased to […]

Importance of Maximal Resistance Training. One of the cardinal principles of muscle development during athletic training is the following: Muscles that function under no load, even if they are exercised for hours on end, increase little in strength. At the other extreme, muscles that contract at more than 50 per cent maximal force of contraction […]

The same basic metabolic systems are present in muscle as in other parts of the body. However, special quantitative measures of the activities of three metabolic systems are exceedingly important in understanding the limits of physical activity. These systems are (1) the phosphocreatine-creatine system, (2) the glycogenlactic acid system, and (3) the aerobic system.
Adenosine […]

In addition to the large usage of carbohydrates by the muscles during exercise, especially during the early stages of exercise, muscles use large amounts of fat for energy in the form of fatty acids and acetoacetic acid, and they use to a much less extent proteins in the form of amino acids. In fact, even […]

Phosphocreatine (also called creatine phosphate) is another chemical compound that has a high-energy phosphate bond, with the following formula:
Creatine ~ PO3-
This can decompose to creatine and phosphate ion, as shown to the left in Figure 84–1, and in doing so release large amounts of energy. In fact, the high-energy phosphate bond of phosphocreatine has more […]

The final common determinant of success in athletic events is what the muscles can do for you—what strength they can give when it is needed, what power they can achieve in the performance of work, and how long they can continue their activity.
The strength of a muscle is determined mainly by its size, with a […]

There are few stresses to which the body is exposed that even nearly approach the extreme stresses of heavy exercise. In fact, if some of the extremes of exercise were continued for even moderately prolonged periods, they might be lethal. Therefore, in the main, sports physiology is a discussion of the ultimate limits to which […]