The first of three cardio sessions this week will train your alactic-aerobic energy system and demand a lot of effort from your legs, heart, and lungs. Alactic-aerobic training is designed to improve your endurance during intense activities by increasing the density of mitochondria in your fast-twitch muscle fibers.
Find a cardio machine—or maybe even an outside track— and go as hard as you can for 10 seconds. After the work interval, you'll rest for 50 seconds. You'll do the whole thing 15 more times. I know it seems like a lot of sets, but when it's all said and done you will do less than 3 minutes of actual work.
Because you have such a long rest period, you need to make sure that you're going as hard as possible for those 10 seconds. Sprint your ass off!