Bill Phillip's Back To Fit: Day 30
As you enter Week 5, you should see an improvement in your conditioning!
The more you work this style of high-intensity interval training into your weekly routine, the greater your endurance will be.
Five weeks in, you should already notice that you can do more cardio circuits before you begin to lose your breath or reach fatigue. Keep your body moving and increase the speed when you are ready.
If you are using a treadmill, kick up the speed. If you are outdoors, test the time lengths of the running portion, or maybe take a run up that hill you may have avoided in the past. You are only out on the cardio machine for 25 minutes, so use every second you have.