If you have been on the exact workout routine for more than a few weeks your results have stagnated. For instance, let's say that for the last year you have been walking 3 miles 3 times a week essentially keeping the same pace and the same course. Even though the effort is still good for your heart, you are now burning fewer calories to do the same walk and your cardio fitness has already peaked. You won't get in worse shape you just won't continue to get better.