The stages of life have been defined by cultures and religions in many ways. In ancient Greece, the human life cycle was mapped in seven-year periods. Today, most people recognize the human life cycle as having four or five distinct stages shared by all humans.

Consisting of a series of body parts including the lungs, diaphragm and nasal cavity, the respiratory system is responsible for transporting oxygen and carbon dioxide to and from muscles and tissues. During exercise, the respiratory system increases to meet the demands of the working muscles.

White dots on the skin can appear on anyone after any type of exercise. People who have certain medical conditions or are taking medications or wearing certain types of fabric may be more likely to develop white spots while exercising.

Poor posture causes aches and pains in joints and muscles. If you have back pain, chances are your posture isn't as great as it could be. Posture, according to the American Chiropractic Association, is how we hold our bodies when we're sitting, standing or laying down.

A muscle tear in your shoulder can make simple tasks difficult, like reaching into a cupboard or grooming your hair. Tears in both the muscles and tendons of the shoulder are common injuries that often produce similar symptoms. Tears range from small to large, with larger tears are more likely to cause pain.

Having a painful urination could be due to numerous conditions, from a simple urinary tract infection to a sexually transmitted disease. When the burning, or painful, sensation begins may vary from individual to individual.

The telltale signs of bad posture may develop from poor sitting, standing or sleeping habits, or from age or the onset of a genetic or chronic bone disease. If you believe that a change in your appearance or health is due to poor back posture, that may be only a symptom of a larger disorder.

A keloid is a scar made of cartilage and forms as a result of an infection. A keloid scar is especially common on the ear due to infections from ear-piercing. Keloid symptoms include pain and itchiness on the scar, as well as a noticeable change in skin texture around the keloid.

Rough, dark patches of skin on the knees are not unusual. Your knees bear the brunt of many physical activities. Children learning to crawl are very hard on their knees, as are the parents who kneel on the floor to interact with them at eye level. Generally speaking, rough patches of skin indicate dryness.

Your digestive and respiratory systems, at first glance, seem very separate in their activities. In reality, however, the systems work together intimately in several ways. The results of respiratory activity allow the digestive tract to function, and vice versa.

Stiffness felt throughout your back muscles comes from increased tension in your muscle tissue. The stiffness and back pain may occur in your upper back -- the thoracic and cervical regions -- or your lower back -- the lumbar region. Causes of increased muscle tension include trauma, overuse and poor posture.

An ankle fracture can produce considerable loss of functional mobility. Once the fracture has healed, most physicians refer patients to physical therapy, which after removal of the cast is a vital step to full recovery.