The Tabata Protocol
It's pretty simple. This workout is best performed on a spin bike or an elliptical trainer. If you really need to, it can be done on a treadmill.
Step 1: Warmup for 5-10 minutes at an easy pace.
Step 2: Perform 8 20-second sprints with 10 seconds of rest in between each one.
For example: Sprint at minute 5:00 (assuming a 5 minute warmup)
Go slow from 5:20-5:30
Go slow from 5:50-6:00
Continue until the 9:00 minute mark.
Step 3: Cool down by moving slower for 3-5 minutes.