Are you stuck in an exercise rut? If your routine's hit a plateau, you're missing out on your best fat-burning chances. Here are three clues that your routine is getting too "comfortable", and how to shake things up:

1

You can sing

Over time, exercise builds your endurance, so your usual routine may not be challenging enough anymore -- which equates to fewer calories burned. The talk test is a simple way to gauge whether you're working your body hard enough: If you can talk or sing with ease during your cardio workout, you should up the intensity level. Speeding up or lengthening workout will get your body in a fat-burning zone -- you'll know you're there when you can't speak more than a few words without taking a deep breath or two.

2

You're doing the same old routine week after week

Doing something new makes exercise less monotonous and gives different muscles a workout. So mix up your routine: Instead of the treadmill, try the bike or stepper, sign up for a new workout class, or try a different walking route. Even updating your iPod playlist with new upbeat tunes helps freshen up your routine.

3

You're slacking off

If you start to see exercise as a chore, you will have all sorts of excuses not to exercise -- whether it's "I don't have time" or "I'm feeling too tired". The solution: Get it done first thing in the morning. Studies show that morning exercisers are more likely to stick with their workout regime. Plus, it revs up your metabolism and boosts your energy for the rest of the day. If waking up early isn't your thing, try making a date with an exercise buddy -- you won't hit the snooze button if you are obligated to meet with a friend.