If you made it a point to go jogging in your 50s, don't feel all those miles underfoot were for naught. A study published online Aug. 27, 2012, in the Archives of Internal Medicine found that the greater your mid-life fitness level, the lower your odds are of developing several chronic diseases, including heart failure, stroke, diabetes, colon cancer and Alzheimer's disease. And for those who did develop chronic diseases, a high level of mid-life fitness was also associated with delaying the onset of these diseases. Mid-life fitness was defined using a formula involving body mass index, blood pressure, cholesterol, smoking, alcohol consumption, glucose levels and age. The research involved more than 18,000 subjects.