You may already know that blood pressure and resting heart rate naturally change by age. But some other strength-based health metrics ― like how long you can stand on one leg and how many push-ups you can do ― can also reveal heart and brain changes. It seems that you can add sit-ups to that list too.A 2007 study found that core strength training seemed to reduce injury in physical jobs (the tests were run on firefighters); a 2015 paper revealed that older people with stronger cores had better balance. If you’re not sure what “strong” really means in this case, though, fear not; experts at the sports and science site