6. Try circuit training.

Circuit training is a great way to work your entire body in a short amount of time. Erin and Tiffany share a simple scheme that works for both the gym and the home. Include this workout in your schedule instead of racking your brains about what exactly to do in the next sports "window". Do 3 to 9 reps depending on your fitness level and time availability. The workout will take from 15 to 45 minutes.