Sprint training is powerful medicine. Studies conducted by Izumi Tabata found that short, intense sprints (by "intense" we mean "run as if the zombie apocalypse is upon you") offer benefits like increased aerobic capacity, fat burning, and production of human growth hormone—the closest thing to the fountain of youth that scientists have been able to find. Try this killer cardio blast:
Sprint for 1 minute Walk/jog for 1 minute Sprint on an incline for 1 minute Walk/jog for 1 minute
Repeat the circuit 3 more times (4 times total), cutting the walk time in half every time.