I just started a new workout challenge and I LOVE it. I am am in pretty good shape. I was running about 6 miles 3-4 times a week. THis new workout is focused on strength training and interval training. It only takes 15-20 minutes to do and its KILLING ME! I can barley move. Its only been two weeks and i can feel myself getting stronger I was skeptical that 15-20 minutes would do anything for me.
It just goes to show that you don't have to add more time on the gym or log more miles to get in better shape. You just have to change your workout.