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 smal

ler 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.

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.

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.

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

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