You've been working out for a while, and it's starting to feel comfortable -- too comfortable. It's time to make it tougher again. Step up the challenge if you recognize yourself in any of these five scenarios.

1. You do the same moves over and over. When you first begin exercising, it can be tough to find an activity you love. Once you do, you want to keep at it, which is great -- but you also need to switch it up. “Your body adapts quickly, sometimes in just a matter of a week, to whatever exercise you’re doing,” says Janice Clark, a personal trainer in Los Angeles. “Once that happens, your body doesn’t have to work as hard, and you burn fewer calories.” The solution: First, make sure you have a well-rounded fitness program that includes aerobic exercise, resistance training, and stretching. By doing these three things, you’ll naturally give your body variety. Then, every week to 4 weeks, change one thing about your workouts. For example, ride the stationary bike instead of running on the treadmill. Push yourself a bit more in one of your cardio workouts, or try a new strength exercise.

2. You talk with friends the entire time. A workout buddy can encourage and motivate you. But if you can easily carry on a conversation while you exercise, you’re not working hard enough, which will make it tougher to achieve your goals, Clark says. The solution: Don't dismiss your buddy, but save the chat for later. When you exercise at a moderate level, you want to work hard enough so that you can only get out a few choppy sentences, not carry on a full conversation. When you work out intensely, you should be able to squeeze out only a few words before you need to take a breath.