workouts are the best

As You WorkOut...

Your lungs are getting stronger. When you do cardio, your brain sends signals to them to help you breathe faster and deeper, delivering extra oxygen to your muscles.

Your motivation is at its peak. Thanks to a flood of endorphins, which trigger the classic runner's high, you feel psyched and energized.

You're fighting flab. "During typical cardio exercise, your body taps mainly fat for fuel," Olson says.

FIT TIP: Push yourself to go harder. The more intensely you do aerobic activity and the longer you do it, the more efficiently your body uses oxygen, and this boosts its fat-blasting power throughout your workout, Olson says.