Overall , the current literature supports clearly the dose-response relationship between physical activity and the seven chronic conditions identified .
Moreover , higher levels of physical activity reduce the risk for premature all-cause mortality .
The current Canadian guidelines appear to be appropriate to reduce the risk for the seven chronic conditions identified above and all-cause mortality
This systematic review examines critically the scientific basis for Canada 's Physical Activity Guide for Healthy Active Living for adults .
Particular reference is given to the dose-response relationship between physical activity and premature all-cause mortality and seven chronic diseases ( cardiovascular disease , stroke , hypertension , colon cancer , breast cancer , type 2 diabetes ( diabetes mellitus ) and osteoporosis ) .
The strength of the relationship between physical activity and specific health outcomes is evaluated critically .
Physical Activity and Coronary Heart Disease Risk in Men: Does the Duration of Exercise Episodes Predict Risk?
Background Physical activity is associated with a decreased risk of coronary heart disease ( CHD ) .  However , it is unclear whether the duration of exercise episodes is important : Are accumulated shorter sessions as predictive of decreased risk as longer sessions if the same amount of energy is expended ? Methods and Results In the Harvard Alumni Health Study , we prospect ively followed 7307 Harvard University alumni ( mean age 66.1 years ) from 1988 through 1993 . At baseline , men reported their  walking , stair climbing , and participation in sports or recreational activities .  For each of the latter activities , they also reported the frequency and average duration per episode . During follow-up , 482 men developed CHD .  In age-adjusted analysis , a longer duration of exercise episodes predicted lower CHD risk ( P trend=0.04 ) . However , after total energy expended on physical activity and potential confounders was accounted for , duration no longer had an independent effect on CHD risk ( P trend=0.25 ) ; that is , longer sessions of exercise did not have a different effect on risk compared with shorter sessions , as long as the total energy expended was similar . In contrast , higher levels of total energy expenditure significantly predicted decreased CHD risk in both age-adjusted ( P trend=0.009 ) and multivariate ( P trend=0.046 ) analyses . Conclusions These data clearly indicate that physical activity is associated with decreased CHD risk . Furthermore , they lend some support to recent recommendations that allow for the accumulation of shorter sessions of physical activity , as opposed to requiring 1 longer , continuous session of exercise . This may provide some impetus for those sedentary to become more active
Overall , the current literature supports clearly the dose-response relationship between physical activity and the seven chronic conditions identified .
Moreover , higher levels of physical activity reduce the risk for premature all-cause mortality .
The current Canadian guidelines appear to be appropriate to reduce the risk for the seven chronic conditions identified above and all-cause mortality
This systematic review examines critically the scientific basis for Canada 's Physical Activity Guide for Healthy Active Living for adults .
Particular reference is given to the dose-response relationship between physical activity and premature all-cause mortality and seven chronic diseases ( cardiovascular disease , stroke , hypertension , colon cancer , breast cancer , type 2 diabetes ( diabetes mellitus ) and osteoporosis ) .
The strength of the relationship between physical activity and specific health outcomes is evaluated critically .