Today's workout in our Better-Body Challenge  is cardio. This 45-minute workout starts at a slower place, but to keep things interesting, the speed picks up toward the end, making this a negative-split run. It takes a little discipline to start slowly and build speed throughout your workout, but when the time comes to run faster, your body will be ready for the challenge. Doing this type of workout consistently will help increase your overall running speed, too. And we love that 45 minutes of cardio is going to burn some serious calories.
If you are new to running, you can still tackle the negative-split run. Start at a comfortable speed and just increase in the increments and times this plan suggests.
If running isn't your jam, try this 45-minute elliptical workout , or bike, swim, or Zumba — it doesn't matter how you get your heart rate up, just keep moving for three-quarters of an hour.
Beginners: You can do this workout. Start at a pace you are comfortable with, and increase your pace in the increments suggested in the plan.