The musculoskeletal system is made up of bones, joints, and muscles. This system gives the body form and support, and protects the body while allowing it to move. Basically, the muscles in this system perform three important body functions: the movement of body parts, maintenance of body parts, and production of body heat.

These muscles all consist of a mass of protein fibers grouped together, and most are of mesodermal origin. And almost all of the muscle fibers you will ever have or need were present at birth. Nearly half of your body mass is muscles, the largest and strongest being in the shoulders, upper arms, hips, and thighs. There are over five hundred muscles in the human body.

Muscle fibers are basically classified according to their size and speed of contraction. There are three main types of muscles. The first is skeletal. Skeletal muscle makes up the largest mass of muscle in the body, and is the type of muscle that is attached to bones and moves the skeleton in a conscious control, so therefore it is a voluntary muscle. Its contractions are short and strong, providing the force needed for movement. The muscle contractions produce and provide some heat needed in the body.

Skeletal muscle tissue is made up of smaller fibers called myofibrils. These myofibrils are composed of even smaller protein filaments. These filaments can be either thick or thin. The thick filaments are made of the protein myosin, and the thin filaments are made of the protein actin. The arrangement of the myosin and actin gives skeletal muscle its striated (or striped) appearance.

Each section of a myofibril is called a sarcomere, and is the functional unit of muscle.

How muscles contract is directly related to their structure. The sliding filament theory is an explanation of how muscle contractions occur. This theory states that the actin filaments within the sarcomere slide toward one another during contraction. But, the myosin filaments don t move. The second type of muscle is smooth, which is found in internal organs and blood vessels. It consists of collections of fusiform cells that don t show its striations under even a light microscope. The most common function of this muscle is to squeeze, which puts forth pressure on the space inside the tube or organ it surrounds. Contractions of smooth muscle are weak and slow compared with the contractions of the other two kinds. The smooth muscle s contractions are generally controlled unconsciously by the autonomic nervous system, so therefore smooth muscle is an example of an involuntary muscle.

Another type of involuntary muscle is the third type, the cardiac muscle, which makes up the heart. Cardiac muscle has cross striations, composed of elongated, branched individual cells that lay parallel to each other. These cells are interconnected and form a network that helps the heart muscle contract efficiently. This muscle consists of tightly knit bundles of cells, interwoven that provide for a characteristic wave or contraction, that leads to a ringing out of the heart ventricle. A unique characteristic is the presence of dark-staining transverse lines that cross the chains of the cells at irregular intervals. Final structures found only in the cardiac muscle are intercalated disks, found at end-to-end contact.

Now then, how can you increase the strength of your muscles? As before, you are born with the number of fibers in a muscle. Rather, muscle strength depends on the thickness of the fibers, and how many of them contract at one time. Thicker fibers are stronger and contribute to muscle mass. Regular exercise stresses muscle fibers slightly, and because of this added work, the fibers increase in size.

Another technique to increase muscle size is the use of steroids. Over a hundred years ago, scientists thought testosterone was the cause of masculine features in males. In the 1930 s scientists tested with anabolic steroids on dogs. The result was an increase in muscle mass. By the early 1950 s athletes in Europe and Russia were using steroids for their competitions. These steroids were noticed after several weight lifting records were beaten by Russian lifters. After this, Dr. Ziegel proved that testosterone was indeed the reason for increased performance. By (1964) all the top steroids were already on the market.

Now, in our times, the majority of steroid users are in their late teens. The most common side effect is water retention. This causes a swelling or puffiness in the neck and facial area of the user. Acne and the formation of abnormally large breast glands are caused. Hypertension (high blood pressure) is another side effect, which leads to more serious cardiovascular diseases, because cholesterol builds up and clogs the arteries. Palpitations, impotence, and jaundice (serious liver disease) are all possible side effects.

The last common side effect of steroids is aggression, also known as roid rage . Some users find this as a positive, it increases their motivation to life more and their intensity in their workouts. The negative side users find is that they are more hostile, which leads to fights and conflicts with family, friends, and co-workers. As stated before, the safest and most natural way to increase muscle size and strength is through regular exercise.