reposted from: pg 73, http://www.who.int/whr/2002/en/whr02_en.pdf
Opportunities for people to be physically active exist in the four major domains of their day-to-day lives: at work (especially if the job involves manual labour); for transport (for example, walking or cycling to work); in domestic duties (for example, housework or gathering fuel); or in leisure time (for example, participating in sports or recreational activities).
In this report, physical inactivity is defined as doing very little or no physical activity in any of these domains.
There is no internationally agreed definition or measure of physical activity. Therefore, a number of direct and indirect data sources and a range of survey instruments and methodologies were used to estimate activity levels in these four domains.
Most data were available for leisure-time activity, with fewer direct data available on occupational activity and little direct data available for activity relating to transport and domestic tasks. Also, this report only estimates the prevalence of physical inactivity among people aged 15 years and over.
The global estimate for prevalence of physical inactivity among adults is 17%, ranging from 11% to 24% across subregions. Estimates for prevalence of some but insufficient activity (<2.5 hours per week of moderate activity) ranged from 31% to 51%, with a global average of 41% across the 14 subregions.
Physical activity reduces the risk of cardiovascular disease, some cancers and type 2 diabetes. These benefits are mediated through a number of mechanisms (22). In general, physical activity improves glucose metabolism, reduces body fat and lowers blood pressure; these are the main ways in which it is thought to reduce the risk of cardiovascular diseases and diabetes. Physical activity may reduce the risk of colon cancer by effects on prostaglandins, reduced intestinal transit time, and higher antioxidant levels. Physical activity is also associated with lower risk of breast cancer, which may be the result of effects on hormonal metabolism. Participation in physical activity can improve musculoskeletal health, control body weight, and reduce symptoms of depression. The possible effects on musculoskeletal conditions such as osteoarthritis and low back pain, osteoporosis and falls, obesity, depression, anxiety and stress, as well as on prostate and other cancers are, however, not quantified here.
Overall physical inactivity was estimated to cause 1.9 million deaths and 19 million DALYs globally. Physical inactivity is estimated to cause, globally, about 10–16% of cases each of breast cancer, colon and rectal cancers and diabetes mellitus, and about 22% of ischaemic heart disease.
Estimated attributable fractions are similar in men and women and are highest in AMR-B, EUR-C and WPR-B. In EUR-C, the proportion of deaths attributable to physical inactivity is 8–10%, and in AMR-A, EUR-A and EUR-B it is about 5–8%.