Physical activity is considered to be the most effective tool for promoting health and warding off many ailments. Humans are exposed to a variety of microorganisms during their lifetime, including parasites, malignant cells, including bacteria, fungus, and viruses. This exposure gives the immune system the capacity to distinguish between substances that the human body may accept or reject, which is in turn governed by antigens and antibodies. While antibodies are B-cell proteins responsible for recognizing and identifying the invader agent (i.e., antigen) to be neutralized or destroyed by the immune system, antigens are any material that the human immune system may recognize to stimulate an immunological response
