It's a deal we strike with our bodies, and by all accounts it's a fair one: "I eat healthfully and exercise; my body improves its shape." Unfortunately, our bodies don't always hold up their end of the bargain. Have you ever experienced a time during which, no matter how much you exercised or how impeccably you ate, the scale didn't budge an ounce? If that scenario sounds all too familiar, you may have been experiencing what is known as a "plateau"--and it can completely undercut your motivation. "I'd say 20-40 percent of people on programs at our fitness center drop out because they get frustrated when they hit a plateau," says Sara Bousfield, a certified personal trainer with the American Council on Exercise and the group exercise program director at TimeOut Fitness Center in San Jose, Calif. "The key is to keep a positive mind-set and hang in there." Here's how.

TIP: Spice things up.

You know that a consistent exercise routine nets better health, a clearer mind and a more beautiful body, but if exercise becomes too much of a routine--the same StairMaster workout day in and day out, for example--you'll likely hit a plateau. "The human body is wonderfully adaptive," says Todd Weitzenberg, M.D., a sports-medicine specialist at Kaiser Permanente Santa Rosa Hospital in California. However, that adaptability also can be our nemesis: "It you place the same exercise stress on the body on a daily basis, it won't be as inclined to change its shape," Weitzenberg adds. A plateau is a sign that your body has, in essence, grown wise to your routine.

Try this Write down three activities such as tennis, kayaking or yoga you will do over the next month that you've never tried before. Those activities will alter the positive stresses on your body and help you break free from a rut. Or simply vary your current routine; for example, do your exercises in a different order--or do different exercises altogether--each time you train, or every few workouts. "Breakthrough workouts" are another effective countermeasure to plateaus; these sessions are either longer or more intense than you are accustomed to and serve to "break through" your plateau.

TIP: Throw in the towel (but just for a few days).

If you've been grinding away at an exercise program for more than four weeks and aren't seeing commensurate pay-offs, then you may need to take time off. "Rest is just as important as exercise in the total body equation," Weitzenberg says. To progress over time and bust a plateau, you must exercise, take time off to rejuvenate, and then come back with a renewed vigor.

Try this Review your exercise program over the past month, and if a period of rest is warranted (if, say, you're doing more than two high-intensity cardio sessions a week or not taking a complete day off between strength workouts), then take a two- to three-day break from exercise. Spend the time that you would normally be working out recuperating: Take a daily nap or a long soak in the tub. You'll come back to your routine better equipped to achieve results.

TIP: Think long-term.

It's important to remember that we all experience highs and lows in our fitness programs; it's how you deal with them that matters most. "People who accept the fitness process in its entirety, and hang in there during the lows, are the ones who succeed over time," Weitzenberg notes. You may not see appreciable gains every single week, but that's OK.

Try this On your work sheet, write down what your ultimate goals are, rather than the smaller steps you're taking to achieve them, also noting how eating right and exercising will benefit your health and well-being in the long--term. Use the successes you've experienced so far, and the goals you'll eventually achieve, to inspire you and keep you on track.

TIP: See the big picture.

Sometimes we obsess over the physical manifestations of working out and eating well, such as getting a tighter butt and slimmer hips or seeing a lower number on the scale. Those things are important and do help you to measure your progress, but exercise and good nutrition also nourish the mind and spirit, reduce stress, bolster your confidence and make you feel more alive. Focus on how your healthy choices continue to help you during physical plateaus and you'll have an easier time sticking with your fitness regimen.

Try this This week, when you work out or eat a healthful meal, consider every positive aspect of what you're doing and write down on your work sheet at least three of your observations. Let your stress melt away with every foot-strike on the treadmill; visualize that salad bathing your cells in strengthening nutrients; notice how your confidence soars when you make it through a workout. Chances are, these thoughts and feelings will refuel your resolve almost as much as losing a pound will.