RT Journal
A1 Lee I
T1 Dose-response relation between physical activity and fitness: Even a little is good; more is better
JF JAMA
JO JAMA
YR 2007
FD May 16
VO 297
IS 19
SP 2137
OP 2139
DO 10.1001/jama.297.19.2137
UL http://dx.doi.org/10.1001/jama.297.19.2137
AB 
Physical activity, while not a drug, can behave like one—it causes many physiological changes in the body (often beneficial for health),1 helps prevent the development of many chronic diseases,2 and is a useful adjunct to drug treatment for many diseases, including cardiovascular disease, cancer, and diabetes.3- 4 Health care professionals, including physicians, are encouraged to prescribe physical activity for health.3- 4 It is plausible that there is a minimum dose of physical activity for health benefits, that these benefits increase with increasing dose, and that beyond a certain dose, adverse effects (eg, musculoskeletal injuries,5 sudden death6) outweigh benefits.