Washington, Oct 27 Fitness level declines with age and begins to drop particularly sharply after age 45, says a new study.

Published in the latest issue of the Archives of Internal Medicine, one of the JAMA/Archives journals, the study claimed that maintaining a healthy body mass index (BMI), not smoking and being physically active are associated with higher fitness levels throughout adult life.

To reach the conclusion, Andrew S. Jackson, P.E.D., of the University of Houston, and colleagues studied 3,429 women and 16,889 men age 20 to 96 who participated in the Aerobics Center Longitudinal Study (ACLS) between 1974 and 2006.

During the study, participants completed between two and 33 health examinations that included counselling about diet, exercise and other lifestyle factors along with a treadmill exercise to assess fitness.

Statistical models showed that while fitness levels declined continuously over time, the decrease was not linear or steady-cardiorespiratory fitness declined more rapidly after age 45.

The decline for men was greater than that for women.

The results also "showed that being active, keeping a normal BMI and not smoking were associated with substantially higher levels of cardiorespiratory fitness during the adult life span studied," the authors write.

"Being inactive and having a high BMI were associated with a lower age at which an individual could be expected to reach threshold cardiorespiratory fitness levels associated with substantially higher health risks," the expert added. (ANI)