10 Things Trainers Wish You Knew About Your Workout

6. A Workout Doesn’t Merit a Post-Gym Pig-Out

When you’re feeling virtuous after you’ve exercised, it’s easy to eat back all the calories you just burned (and then some). If you’re looking to lose weight, that won’t help you toward your goal, says Molly Morgan, a registered dietitian and a board-certified sports nutritionist in Vestal, New York. (It’s not OK to collapse on the couch afterward, either: In a 2009 study published in Medicine & Science in Sports & Exercise, long periods of sitting were associated with an increased risk of death, even for exercisers.)

Action plan: To stave off grazing after exercising, have a healthy snack an hour or two after your workout. And stay mobile as much as possible. Take the stairs, do a loop around the office, or pace while you’re on a conference call.

7. Bad Form Is Bad News When You’re Strength-Training

“When I see someone lifting weights with improper form, I get concerned,” says Sokol. “Not only can it diminish results but it can also lead to injury.”

Action plan: Even if you’ve been weight-training for a while, it’s a good idea to brush up on form. You can find videos that illustrate good lifting form on ExRx.net. Or, even better, invest in a session with a personal trainer. A few general tips: Count “one one-thousand, two one-thousand” as you lift the weight, says Sokol, and “one one-thousand, two one-thousand” as you lower it. “If you lift too fast, you let momentum, not your muscles, do the work,” he says. When doing upper-body exercises, keep your wrists straight; when doing squats and lunges, align your knees and ankles; and when bending over for an exercise (like a dumbbell row), keep your back flat. Always keep your neck aligned with the rest of your body.

8. Working Out on an Empty Stomach Won’t Burn More Fat

A common belief is that if you exercise before you eat, your body will turn to its fat reserves for energy instead of the food in your stomach. In fact, it’s just the opposite: In a 2011 study published in the International Journal of Sport Nutrition and Exercise Metabolism, people experienced a bigger boost in metabolism—meaning, burned more fat—when they exercised after eating breakfast than when they did the same workout on an empty stomach. The authors of the study theorize that when you eat before exercising, your body uses more oxygen, resulting in a metabolism spike and an improvement in fat burning.

Action plan: Eat already! Even a small snack with carbohydrates, protein, and a little fat, eaten a half hour before, will power your workout, says Morgan. Good choices: low-fat yogurt and a banana, whole-grain cereal and low-fat milk, or oatmeal and fruit. Or make it really easy and choose a fruit-and-nut bar, such as a Lärabar ($28 for 16, larabar.com).