The fatigue index is a concept used in the study of the development of fatigue during anaerobic exercise. Anaerobic exercise consists of activities -- such as sprinting -- that rely on glycogen rather than oxygen for fuel.

The immune system is responsible for keeping the body healthy and protecting against sicknesses and infections. When someone has a poor immune system, due to a disease such as AIDS or cancer, they are more likely to get sick easily.

Pain in your lymph nodes or body glands can be the result of swollen glands due to infection. However, pain in the areas surrounding your glands can also stem from an injury and the resulting radiating pains.

Toxins and free radicals can build up in your body, causing cellular damage and illness. Diet and exposure to environmental toxins can damage the mitochondria in your cells — vital microorganisms that help convert food to energy.

The dome-shaped cornea covers your eye. The space between the cornea and your iris contains fluid called aqueous humor that nourishes the surrounding tissues. If you have thin corneas, you may have an increased risk for corneal damage or misdiagnosis of eye conditions.

Early HIV infection causes symptoms in most women and men. However, these symptoms are often so mild that they are overlooked or attributed to another illness. Here's what you need to know about early HIV symptoms in women.

While the number of people newly diagnosed with HIV infection in the world has fallen by about a third since 2000, HIV remains a significant health problem. According to the United Nations Programme on HIV/AIDS, there were almost 37 million people around the world living with HIV/AIDS in 2014.

Cordyceps is a medicinal fungus, or mushroom, (See Ref 1) with a long history of use in Traditional Chinese Medicine. People take it for a variety of purposes, including to promote healthy blood sugar levels, reduce fatigue and for anti-aging.

Fatigue (bodily or emotional weakness) and lack of energy typically go hand in hand. Though both symptoms are common and often mild, persistent or extreme cases may indicate a serious underlying condition, such as depression, testosterone deficiency or a sleep disorder.

Gluten is a type of protein found in wheat, rye, barley and related grains, such as spelt and farro. It may also be added to processed foods as a thickening agent. When you have celiac disease, your body reacts negatively to gluten, resulting in damage to your small intestine.

Children require adequate sleep each day to function properly. A 4-year-old who appears to be tired all day may be suffering from too little sleep. When specific symptoms are present, the fatigue could be due to an illness.

The lymphatic system includes the lymph nodes and their connecting vessels as well as the tonsils, spleen and appendix. The nodes act as stations that help to filter out toxins, debris and pathogenic organisms that may be coercing through the lymphatic vessels.