Exercise is the single best way to torch more calories all day long. Don’t let these mistakes rob you of your postworkout burn.

Mistake #1: You’re in an exercise rut

When you do the same activity day after day, week after week, your mind isn’t the only thing that gets bored—your muscles do, too. Whether you take the same daily 30-minute walk around the neighborhood loop, or do a few sets of the same old strength moves, after a while your body stops being challenged and your results plateau.

Correct it: Change things up. Go for a hike on the weekend instead of doing your usual power walk. Find new strength moves that work the same muscles. Try a new type of exercise by slipping in a workout DVD. Any little way to mix things up and challenge yourself with something new is a step in the right direction.

Mistake #2: You’re a slave to cardio

While aerobic exercise is good for your body and soul, if you don’t balance those workouts with some strength exercises, you’re not only compromising your results but missing a key component of health and fitness. Resistance training—weight lifting, or strength training—is the only way to increase lean muscle mass and lose stubborn bulges. That’s important on many levels, especially as we start to get older.

Starting in their 30s, women lose about 1/2 pound of muscle a year. (Men usually hold on to muscle longer, but the rate of muscle loss speeds up dramatically after age 60.) Because muscle burns calories even when at rest, losing it will noticeably slow metabolism. This is one big reason many of us see that “middle-age spread” beginning in our 40s.

A study from Skidmore College found that exercisers who combined cardio with a high-intensity, total-body resistance routine lost more than twice as much body fat—including twice as much belly fat—over 12 weeks as those who followed a moderate-intensity cardio plan.

Correct it: Substitute a couple of strength sessions for cardio days. Lift weights at least twice a week, hitting all your body’s major muscle groups.

Mistake #3: You’re stuck in a “fat-burning” zone

If you hop aboard a treadmill, elliptical trainer, stair climber, or other cardio machine at the gym, you may see a programming option that allows you to stay in a “fat-burning” zone. It’s based on the fact that at lower intensities, the body uses a greater percentage of its fat stores for fuel. Sounds great! You don’t have to work as hard and you’re sucking some of that fat out of your belly, butt, and thighs.

But do the math and you’ll see the problem. At a lower intensity level, your body will indeed burn a higher percentage of fat than carbs but still burn fewer calories overall. Here’s an example. A 150-pound woman who walks on the treadmill at 3 mph (a 20-minute mile) burns about 112 calories in 30 minutes. At this moderate intensity, she burns about half of those calories from fat, or about 56 fat calories. If she were to take that workout into a brisk walk for 30 minutes at 4 mph (a 15-minute mile), only about 40 percent of her calorie burn might be from fat. But she’d be burning more calories overall—about 170 in those 30 minutes, or about 68 calories from fat.

Correct it: Burn more calories and make more of those calories come from fat by increasing your overall effort. A great way to achieve that is by doing intervals—periods of higher intensity followed by a slower recovery pace.