Muscle pain, spasms and cramping in the back of legs can develop for a variety of reasons. Simply straining the muscles can cause discomfort between the thighs and calves. In some cases medical conditions may lead to muscle aches or sharp pain in the back of upper legs and behind the knees.

Degenerative disc disease occurs over time as your spinal column performs everyday activities and weakens. Herniated discs occur when the interior of a spinal disk is squeezed out through a weakened section of the disk, placing additional pressure on surrounding nerves and irritating them.

Inversion therapy is nothing new. Hanging upside-down to relieve pain and the effects of gravity have been documented as far back as 400 BC when Hippocrates, the famous physician, observed a patient being hung by his knees and ankles from a ladder to relieve an ailment.

Inversion boots, or gravity boots, are fitness gadgets that wrap around your ankles, allowing you to hang upside down from a bar. They are used in inversion therapy to apply traction to your back with the goal of decompressing the vertebrae of your spine.

Inversion tables allow you to safely and easily hang upside down for partial or full inversion. Partial inversion, which takes you less than 90 degrees, will decompress your spine, according to Body Flex Sports Inc. Full inversion provides maximum stretching.

A lumbar disc herniation occurs in the lower back and results in symptoms such as sharp or dull back pain, muscle spasm, leg weakness and sciatica. Lumbar disc herniations are common problems, affecting an estimated 1 to 2 percent of Americans, according to a September 2006 article in "

Sciatica is a painful condition that can also lead to weakness and numbness in the low back, hips and legs. The first step in treatment is to diagnose the underlying problem that is causing the sciatica nerve to be irritated.

Regular exercise is the best way to prevent lower back pain, but you shouldn't exercise while you have severe back pain, according to "Low Back Pain," a report by The Merck Manuals Online Medical Library.

Lower back pain is the most common work-related disability. Most instances disappear after a few days -- if your pain lasts for more than three months, it's considered chronic. Low-impact exercises, especially walking, are appropriate activities if you suffer from recurring lower back pain.

Swelling that takes place in the body is a result of inflammation. Usually, inflammation is the body's response to infection such as bacteria and viruses. According to the Cleveland Clinic, white cells within the immune system trigger inflammatory chemicals that are meant to protect the body.

While the reverse crunch effectively trains your abdominals, it can be a painful exercise to perform for some individuals. The way the reverse crunch is performed plays a large role in keeping the exercise pain free; however, some people will require modifications to the exercise so that pain does not occur.

Large breasts might be visually desirable, but can be physically painful, causing back, neck and shoulder discomfort and deformity. If your breasts are too large, you might feel self-conscious and you might have trouble finding clothes that fit the way you like.