Muscle atrophy is the wasting or thinning of muscle mass. It can be caused by disuse of your muscles or neurogenic conditions. Symptoms include a decrease in muscle mass, one limb being smaller than the other, and numbness, weakness and tingling in your limbs.

While not all cases of muscle wasting can be reversed or improved, some can, especially those related to physical inactivity. In fact, exercise is the most essential treatment for muscle wasting, along with eating a nutritious and protein-rich diet.

In cachexia, your body changes dramatically as you lose weight and muscle and become increasingly weak. It affects your quality of life and can be life-threatening. Right now, the only treatment for cachexia involves managing the underlying condition and taking steps to improve nutrition.

"Without question, exercise is the most powerful intervention to address muscle loss, whether it occurs in the context of advancing age or debilitating chronic or acute diseases," explains Nathan K. LeBrasseur, Ph.D., of the Department of Physical Medicine and Rehabilitation at Mayo Clinic in Rochester, Minn. "However, researchers are also ...