The heterogeneity in reported effects was reduced in higher quality studies , when physical activity was self-directed with some professional guidance and when there was on-going professional support .
Our review suggests that physical activity interventions have a moderate effect on self reported physical activity and cardio-respiratory fitness , but not on achieving a predetermined level of physical activity .
Due to the clinical and statistical heterogeneity of the studies , only limited conclusions can be drawn about the effectiveness of individual components of the interventions .
BACKGROUND Little is known about the effectiveness of strategies to enable people to achieve an increase in their physical activity .
OBJECTIVES To assess the effects of interventions for promoting physical activity in adults aged 16 years and older , not living in an institution .
Physical activity and risk of developing colorectal cancer among college alumni.
The assessment of physical activity at a single time to evaluate its association with cancer may be limited , since such a measure may not adequately reflect activity over the long term . To overcome this limitation , we studied 17,148 Harvard alumni aged 30 - 79 years who were followed prospect ively for the occurrence of colon cancer ( n = 225 ) and rectal cancer ( n = 44 ) from 1965 through 1988 .  Physical activity , based on self-reported stair climbing , walking , and sports play , was assessed in either 1962 or 1966 ( 1962/1966 ) and again in 1977 . The increased activity evaluated using either assessment ( 1962/1966 or 1977 ) taken alone was not associated with risk of colon cancer . However , alumni who were highly active ( energy expenditure of greater than 2500 kilocalories/wk ) at both assessment s had half the risk of developing colon cancer relative to those who were inactive ( less than 1000 kilocalories/wk ) at both assessment s ( age-adjusted rate ratio = 0.50 ; 90 % confidence interval = 0.27 - 0.93 ) , whereas those who were moderately active ( 1000 - 2500 kilocalories/wk ) at both assessment s had an age-adjusted rate ratio of 0.52 ( 90 % confidence interval = 0.28 - 0.94 ) . We conclude that either consistently higher levels of activity are necessary to protect against colon cancer or combining two assessment s increased the precision of physical activity measurement . We found no evidence that increased physical activity protected against rectal cancer
The heterogeneity in reported effects was reduced in higher quality studies , when physical activity was self-directed with some professional guidance and when there was on-going professional support .
Our review suggests that physical activity interventions have a moderate effect on self reported physical activity and cardio-respiratory fitness , but not on achieving a predetermined level of physical activity .
Due to the clinical and statistical heterogeneity of the studies , only limited conclusions can be drawn about the effectiveness of individual components of the interventions .
BACKGROUND Little is known about the effectiveness of strategies to enable people to achieve an increase in their physical activity .
OBJECTIVES To assess the effects of interventions for promoting physical activity in adults aged 16 years and older , not living in an institution .