Atrophy : forced bed rest or loss of neural stimulation can result in atrophy, which is degeneration and loss of muscle mass. Atrophy begins as soon as the muscles are immobilized -- and muscle strength can decrease as much as 5% a day.
Muscular Dystrophy : refers to a group of related, inherited muscle-destroying diseases. Symptoms usually appear during childhood.
 | Duchenne muscular dystrophy is the most common; it is a sex-linked recessive condition. Victims typically have a life span of only 20-25 years, as their deteriorating muscles can no longer support life. The cause is lack of a protein called dystrophin which is important in maintaining the integrity of the sarcolemma. |
| myotonic dystrophy is another sex-linked condition that arises as the result of a triplet repeat |
Muscle cramps : are sustained spasms (tetanic contractions) of an entire muscle. They can last minutes, hours or days. The muscle becomes taut and painful. Causes include low blood sugar levels, electrolyte depletion (esp. calcium or sodium), dehydration, or irritability of the spinal cord neurons. Squeezing and stretching (simultaneously) of the muscle may help. The most common type is the "charley horse."
Muscle spasm : a sudden involuntary muscle twitch, which may be painful depending on its severity. Psychological factors may play a role in eyelid or facial spasms, but chemical imbalances are thought to play a role too. Massage may help to end the spasm.
Muscle strain : not to be confused with a joint sprain/strain. It is commonly called a pulled muscle. It is caused by excessive stretching and possible tearing of the muscle due to overuse or abuse. The muscle becomes inflamed and any adjacent joints become immobilized to some degree.
Overuse Injuries : heavy workouts without a proper rest period (a day or more) can result in an overuse injury where the muscles are never allowed to rest and repair. This can result in a permanent injury or disability
Tetanus : as a disease, tetanus is an acute disease caused by the toxin of the anaerobic bacterium Clostridium tetani, which can thrive in a puncture wound. It starts as a stiffness in the jaw and neck, progressing to fixed rigidity of the jaw (lockjaw), and leading to painful spasms of the trunk and limb muscles. It usually will result in death if not treated due to respiratory failure or exhaustion.
