I am a fan of mixing up my cardio pace — long, slow runs for endurance, tempo runs for speed, and interval training for a mixture of the two. Lately, I have a hard time revving up for my higher intensity workouts, since they're hard. I have a new piece of motivation though: Vigorous exercise raises levels of fat-burning hormones, which means more bang for my cardio investment. These hormones raise the level of calories burned post-workout, known as the afterburn.
Adding shorter but faster-paced workouts to your fitness regimen will help you decrease total body fat. High intensity workouts help decrease the amount of visceral fat, too — that's the dangerous fat that surrounds the liver and kidneys associated with diabetes and heart disease. One last reason to up the intensity is that it will also save you time, since you can burn the same calories in a shorter amount of time. If you walk for exercise, you can still work at a higher intensity and aim to walk at a very brisk 4.5-mile-per-hour rate.