Fitness is generally understood to mean physical and often also mental well-being. Fitness expresses the ability to perform in everyday life and to withstand stress more readily. The term is imprecise in that, as a fashionable term, it cannot be clearly defined and is interpreted differently by different people and interest groups.
The risk of diseases of civilization such as heart attacks and obesity can be reduced by targeted fitness training. The ability to concentrate and learn is increased. People who actively keep fit are considered healthier and, statistically, have a longer life expectancy.
Fitness of body and mind includes regular physical activity on the one hand, and a healthy, balanced diet rich in nutrients and fiber on the other. Unhealthy supplements (doping, anabolic steroids) are just as incompatible with fitness as the restriction to pure strength training.