Misconceptions about exercise can sabotage your efforts to get in shape. Here are some common myths — and the facts.

MYTH: Your routine isn’t working if you’re not losing weight.

Do yourself a favor and pay less attention to the scale. Exercise has a small impact on weight loss over the short term. While wanting to look good is a reasonable goal, exercise also provides numerous health benefits, including a lower risk of heart disease and stroke. If you want to shed pounds in addition to getting in shape, try cutting calories while you step up your workouts.

MYTH: A pedometer is all you need to track your exercise.

Pedometers are an excellent way to monitor overall daily activity and help keep you motivated. But counting steps isn’t a reliable way to measure exercise intensity or quality. It’s better to use a heart-rate monitor to track intensity, and aim for a target heart rate for a set number of minutes rather than a certain number of steps.

MYTH: You don’t have to lift weights.

Actually, strength training is critical for older adults to help prevent age-related bone and muscle loss, both of which can lead to falls and other serious injuries. Strengthening your muscles also decreases your body-fat percentage and increases the rate at which your body burns calories, which can help with weight management. Women in particular shouldn’t worry that they’ll pack on too much muscle mass by lifting weights because they have relatively low levels of the male hormone testosterone, which affects muscle growth.

MYTH: As long as you get regular exercise, it’s fine to be a couch potato at other times.

Research has found that sitting for long periods actually causes a slight increase in the risk of several diseases, including heart disease, Type 2 diabetes and possibly cancer — even among people who meet recommended levels of daily exercise. Find ways to spend less time sitting. A useful goal is to replace six to seven hours a week of sitting time with something you do on your feet, whether it’s walking, playing a sport or just puttering around your home or office. And try to cut your evening screen time.

MYTH: You can lose fat from specific parts of your body.

There’s no such thing as “spot reduction.” The calories you expend during exercise help burn fat from your entire body, including whichever areas you’re targeting. What’s more, concentrating your exercise on a specific body part can actually limit the benefits of training, since other muscle groups might be neglected.

MYTH: You should stretch before a workout to avoid injuries.

Researchers have discovered that’s not the case. In terms of increasing flexibility, your muscles will benefit more from stretching when they’re warm, after your workout. Stretching cold muscles could actually injure them.

MYTH: It’s better to have a sports drink than plain water during exercise.

A sports drink is necessary only when you’ve lost a substantial amount of sodium and other electrolytes through sweating or if you need extra carbohydrates to burn for energy. Aim to drink 17 to 20 ounces of water during the two to three hours before a demanding workout and another seven to 10 ounces every 15 minutes while exercising. Continue to rehydrate with plain water afterward.

MYTH: Exercising before bedtime will help you sleep better.

Sleep experts don’t recommend working out close to bedtime, even up to three hours before, according to the National Sleep Foundation. Exercise has a stimulating effect and elevates body temperature, both of which can make it difficult to sleep. But the corresponding fall in temperature five to six hours after exercise actually makes it easier. So aim for a workout earlier in the day if you have trouble sleeping.

MYTH: Calorie counters on exercise machines are accurate.

Don’t count on it, especially if the machine doesn’t ask for your weight, height and sex. According to the American Council on Exercise, manufacturers use formulas to account for intensity and duration. If you want to make sure you’re using the most up-to-date formula, call the manufacturer to see if someone can walk you through an upgrade over the phone. Experts suggest trying to burn at least 1,000 calories a week through exercise, though less than that can still have benefits. Any exercise is better than none.

2012. Consumers Union of United States Inc.