im not up on the science but cardio capabilities are important to me and sprints are def a part of my routine. a good way to get into sprints is to do 30/60's and move into 60/120's. what i mean by that is sprint as hard as you can for 30 sec and then jog or walk depending on your abilities and for 60 sec. same for 60/120's. this can be applied to the stationary bike as well. good for improving cardio endurance and of course all out sprinting.
another way is to go to a basketball court or tennis court and run the lines. start at the rear line, run to the first, back to the line you started, out to the next, return, and so on.