According to Dr. Al Sears, widely respected healthcare and fitness expert, the number one predictor of how long you will live is your lung power. The typical high intensity cardiovascular endurance training is not for the typical deconditioned people. They are not ready for extreme workouts. Also, this training does not make lungs strong and healthy. It shrinks them!
His sensible PACE program is designed for anyone at any fitness level and designed to progressively challenge your system through incremental increases in exertion.
More information can be found on YouTube: https://www.youtube.com/user/AlSearsMd/videos.