Physical activity is defined as any voluntary bodily movement produced by skeletal muscles that requires energy expenditure.^[1] Physical activity encompasses all activities, at any intensity, performed during any time of day or night.^[2] It includes both exercise and incidental activity integrated into daily routine. This integrated activity may not be planned, structured, repetitive or purposeful for the improvement of fitness, and may include activities such as walking to the local shop, cleaning, working, active transport etc. Lack of physical activity is associated with a range of negative health outcomes, whereas increased physical activity can improve physical and mental health, as well as cognitive and cardiovascular health.^[3] There are at least eight investments that work to increase population-level physical activity, including whole-of-school programmes, active transport, active urban design, healthcare, public education and mass media, sport for all, workplaces and community-wide programmes.^[4][5] Physical activity increases energy expenditure and is a key regulator in controlling body weight (see Summermatter cycle for more).^[6]

"Exercise" and "physical activity" are frequently used interchangeably and generally refer to physical activity performed during leisure time with the primary purpose of improving or maintaining physical fitness, physical performance, or health. However, physical activity is not exactly the same concept as exercise. Exercise is defined as a subcategory of physical activity that is planned, structured, repetitive, and purposeful in the sense that the improvement or maintenance of one or more components of physical fitness is the objective.^[1] Conversely, physical activity includes exercise but may also be unplanned, unstructured, random and non-purposeful carried out for a multitude of reasons.

A 2021 study shows that people who start successful physical activity programmes maintain much of it for at least three months.^[7]

Physical activity can be at any intensity, from a simple twitch of a muscle to an all-out sprint. In practice, physical activity can be viewed as a continuum from sedentary behavior to vigorous intensity activity. Intensities are broadly categorized according to energy expenditure using a standard measure of intensity, metabolic equivalents (METs). The broad categories are sedentary behavior, light activity, moderate activity and vigorous activity.

Many studies have demonstrated the potential beneficial effects of physical activity on the prevention and therapy of many disorders as Obesity^[8][9] and Irritable bowel syndrome ^[10][11] Physical activity has been shown to reduce anxiety as a condition (individual physical exercise, without continuity), anxiety as a personality trait (continuous performance, "exercise" of certain physical activities), psycho-physiological signs of anxiety - blood pressure and heart rate (moderate physical activity can lead to a decrease in the intensity of short-term physiological reactivity and encourage recovery from short-term physiological stressors (Biddle et al., 2000)). For people with a severe depressive episode and anxiety disorder, long and short walks proved to be the most effective; for people with substance abuse disorders, bipolar disorder and frequent psychotic decompensation, "strenuous" gymnastics and riding proved to be the most effective.^{[medical citation needed]} Reducing workplace-base sitting has been shown to address sedentary behaviour in workplace. However, there are few interventions that are cost-effective in reducing occupational sitting time. ^[12]

Different forms of physical activity in leisure time can be divided into different clusters of activities that have a common denominator in the form of type of meaningfulness, se model to the right (Lundvall & Schantz 2013).^[13]

These separate forms of meaningfulness consist of (i) competition and championship, (ii) nature encounters, (iii) aesthetic-expressive, (iv) fitness gymnastics and play, (v) everyday exercise and (vi) five different basic forms of physical training (aerobic, anaerobic, strength, flexibility and coordination training).

How these different clusters have been treated over time from 1813 to today in a context of teacher training for physical education in the Swedish school system has been described by the Swedish professors in human movement science Suzanne Lundvall & Peter Schantz (2013).^[14]

Physical activity, qualified in the form of a physical activity vital sign (PAVS) metric, has been proposed as a screening tool in primary care diagnostics.^[24] It has been suggested to correspond with BMI^[25] and chronic disease, when coupled with demographic information^[24] as well as a tool for identifying patients who do not meet certain physical activity guidelines.^[26] Generally, this metric is evaluated by a self-reported medical questionnaire, which can significantly affect the validity and applicability of a PAVS in clinical treatment determination.^[24][26]

• Physical inactivity