Are you working your butt off but noticing not much of a change in your body? Could be something simple holding you back. Like your posture.

Slumping while doing cardio ups your heart rate, says one recent study cited in Prevention magazine. The result: Your workout is harder. Try pulling back your shoulder blades next time you hop on your favorite machine and you'll notice that you're able to take in more oxygen. Your pace should pick up. And you'll burn more calories too.

A little posture goes a long way. Give it a try.