Physical fitness and physical activity are two terms that are often used interchangeably, but they have distinct definitions.
Physical fitness is the ability to carry out daily tasks energetically without undue fatigue, encompassing aspects like endurance, strength, flexibility, balance, and more. Physical activity, on the other hand, refers to any movement that burns energy beyond a basal level.
A sedentary lifestyle has serious consequences. Both short-term and long-term inactivity can lead to chronic diseases, including type 2 diabetes, cardiovascular disease, obesity, and premature death. Inactivity can also speed up secondary aging of muscles and reveal obesity phenotypes that are preventable with physical activity.
The modern world has engineered most physical activity out of daily life, allowing humans the choice to be inactive. This has led to a widespread increase in chronic health problems. For example, daily tasks performed without machines can burn significant calories, and the reduction in this energy expenditure contributes to weight gain.
Research shows that even reducing daily physical activity in the short term can lead to loss of cardiorespiratory fitness (CRF), insulin sensitivity, and lean mass, and an increase in fat. Individualized medicine, accounting for genetic factors and responsiveness to exercise, is seen as a way to personalize prevention against diseases.
Ultimately, physical activity is a fundamental requirement for human health, just like food and reproduction. Lack of activity affects nearly every part of the body, leading to dysfunction and accelerated death.
Physical activity is vital not only for survival but also for maximizing both health span and lifespan, and it should be prioritized in prevention and therapy. Structured exercise programs can improve CRF and lean body mass, while small changes in daily habits can increase calorie output.
Booth, Frank W et al. “Lack of exercise is a major cause of chronic diseases.” Comprehensive Physiology vol. 2,2 (2012): 1143-211. doi:10.1002/cphy.c110025