Pain from exercise does not automatically appear during the routine. Discomfort after the fact is common. However, severe pain is always a concern. Lower back discomfort may be a sign of an injury and not just normal muscle ache.

Pulled muscles in the shoulder and neck can happen during overhead movements or heavy lifting. Even simple actions can cause neck or shoulder strain in muscles that have been stressed from overuse or poor posture.

Painful leg cramps are common, affecting approximately 50 to 60 percent of adults and 7 percent of children. They usually occur at night, and most often affect the calf, foot, and thigh muscles.

A herniated disk occurs when the soft center of a disk in your spinal column seeps out. A herniated disk may result from poor postural habits or degenerative disk disease because of aging or a decrease in the water content of the disks.

You might not need to do the middle splits frequently in your everyday life, but having the inner-thigh flexibility for splits comes in handy during a number of pursuits, such as martial arts, dance and rock climbing.

The sartorius muscle can suffer injury when excessive force causes the upper leg to stretch beyond its capacity. Tissue fibers may partially separate or fully tear, weakening the leg and restricting its motion.

A tumor composed of dilated blood vessels that grows along the bones in the spinal cord is a condition called a vertebral or spinal hemangioma. People with this type of spinal tumor typically don't experience symptoms, especially when the hemangioma is small.

The muscles of the back are surprisingly strong but are meant largely to engage in continuous, low-intensity efforts. Requiring them to move quickly or contract strongly, as they must to lift a very heavy weight, can pull them, leading to painful aching and spasms.

A bone fracture occurs when stress or impact separates a bone. It may be a complete fracture, in which the bone breaks all the way through, or an incomplete fracture, in which the bone cracks but does not separate. When a fracture occurs, your body must produce new bone cells to repair the break.

Lumbar scoliosis is a sideways curvature of the spine that occurs in the lower back. Most cases of scoliosis are mild, but can be severe if the curvature begins to affect the heart and the lungs. Scoliosis can also cause misalignment in bones of the body and chronic pain in the back.

The knee joint is not immune to sprains, strains and other running-induced injuries. If you have a knee bone bruise following a run, it could signify a problem. Training too hard, twisting motions -- like a sudden turn while running -- and improper stretching technique can all contribute to knee injuries in runners.

Better posture can make you look both taller and thinner. When you hunch over or slouch, you immediately lose inches off of your height, which can also make you look heavier. By improving your posture, you can look taller without ever growing.