Physical activity boosts the immune system. This is dependent on the concentration of endogenous factors (such as sex hormones, metabolic hormones and growth hormones), body temperature, blood flow, hydration status and body position. Physical activity has shown to increase the levels of natural killer (NK) cells, NK T cells, macrophages, neutrophils and eosinophils, complements, cytokines, antibodies and T cytotoxic cells. However, the mechanism linking physical activity to immune system is not fully understood.
According to the Centers for Disease Control and Prevention (CDC), physical fitness is defined as 'the ability to carry out daily tasks with vigor and alertness, without undue fatigue, and with ample energy to enjoy leisure-time pursuits and respond to emergencies.' Based on this definition, fitness involves everything from getting out of bed to hiking to performing CPR.
Sam Ashe-Edmunds has been writing and lecturing for decades. He has worked in the corporate and nonprofit arenas as a C-Suite executive, serving on several nonprofit boards. He is an internationally traveled sport science writer and lecturer. He has been published in print publications such as Entrepreneur, Tennis, SI for Kids, Chicago Tribune, Sacramento Bee, and on websites such Smart-Healthy-Living.net, SmartyCents and Youthletic. Edmunds has a bachelor's degree in journalism.