The "Fast 15"
Do this workout when you're pressed for time. Jog for three minutes. Then increase the speed to a faster pace and hold it for two minutes (it's okay if you're huffing and puffing a bit by the end). Walk for 30 seconds. Repeat the sequence. Next, extend the run portion to three minutes. Walk for 30 seconds. Repeat. Cool down with a short walk.
The Pace Booster
Warm up for six minutes by alternating 30 seconds jogging with 30 seconds walking. Then increase your speed slightly and run for 30 seconds. Walk for 30 seconds. Continue this 30/30 ratio. Increase your speed slightly with each successive run segment. Do as many cycles as you comfortably can.
The Distance Run
Increase your speed until you're running comfortably. Run for two minutes, then walk for one minute. Repeat this 2:1 ratio three times. Bump up the ratio: Run for three minutes, then walk for one minute. Repeat three times. End the workout by running two 2:1 segments, followed by two 1:1 segments.
The Hill Climb
Gradually increase your speed until you're at easy-run pace. Run for three minutes. Raise the incline to 2 percent for one minute, then to 4 for one minute. Lower the incline and rest for one minute. Raise to 4 percent and run for two minutes. Alternate running two minutes at an incline/jogging one minute on the flat for as long as you can.