Physical fitness is the state of health and well-being that enables individuals to perform sports, occupations, and daily activities effectively. Historically, fitness simply meant the capacity to perform daily tasks without undue fatigue, but the modern definition has evolved to encompass the body's ability to function efficiently in work, leisure, and emergency situations, alongside resisting disease and improving immune function. A significant shift occurred around 1950, following the Industrial Revolution and World War II, when the term "fitness" surged in popularity and became intertwined with physical attractiveness, fueling the global fitness industry. Beyond physical health, fitness is recognized as a holistic concept—often depicted as a triangle of physical, emotional, and mental well-being—and it provides substantial benefits in treating anxiety, depression, and chronic conditions while improving sleep. The 2018 Physical Activity Guidelines for Americans (issued by the U.S. Department of Health and Human Services) provide science-based recommendations, suggesting adults should engage in 150 to 300 minutes of moderate-intensity or 75 to 150 minutes of vigorous-intensity aerobic activity weekly for substantial health gains. Modern research also reveals that exercise benefits are mediated by contracting muscles releasing myokines—substances that promote tissue repair and anti-inflammatory functions, reducing the risk of various inflammatory diseases.