IB Sports, exercise and health science A.3.2.2 Effects of Physical Activity on the Muscular and Immune Systems Key Definitions

White blood cells responsible for producing antibodies that fight off pathogens.

A hormone produced during stress that, in excess, can suppress immune function and impair immune responses.

A cytokine is a protein that acts as a chemical messenger to regulate the immune system.

Muscle pain and stiffness that occurs after intense exercise, usually within 24–72 hours, caused by microscopic muscle tears that occur during eccentric muscle contractions.

Fatigue refers to the reduced capacity of muscles to perform due to prolonged exertion.

Hypertrophy refers to the increase in the size of muscle fibers.

Immune system is the network of cells, tissues, and chemical messengers that protects the body from pathogens and removes damaged or abnormal cells.

Leukocyte (white blood cell) is an immune cell that defends the body against infection. Subtypes include lymphocytes, neutrophils, and monocytes.

Cells that engulf and digest pathogens and dead cells, playing a crucial role in immune defense.

Open window is the period of immune suppression that follows a bout of prolonged, high-intensity exercise. During this time the athlete is more susceptible to infection.

Pathogen is a microorganism such as a virus, bacterium, fungus, or parasite that can cause disease in the body.

Sleep hygiene is the set of habits that promote good sleep: consistent bed and wake times, a wind-down routine without screens, and a cool, quiet, dark bedroom.

White blood cells that play a central role in the immune response, particularly in identifying and killing infected cells.

Upper respiratory tract infection (URTI) is an infection of the nose, sinuses, throat, or larynx, usually viral. URTIs are the most common acute illness in athletes during heavy training.