Liz Neporent is a diet and fitness expert and author of 12 fitness bestsellers. She regularly appears on national TV programs and is the president of Wellness 360, a New-York based wellness provider.

It's so frustrating when you make an effort to lose weight -- an honest-to-goodness, try-your-heart-out effort -- and it goes nowhere. (Of course, who doesn't feel a smidge of impatience right from the get-go? There's always a little part of you that expects to be transformed after just one workout.) My clients often cite lack of results as one of the top reasons for giving up on an exercise. So, for those who have ever felt like they've been left at the starting gate when trying to lose weight by exercising, here are a few tips that may help.

Work Harder. When you first begin an exercise program, even a leisurely stroll can leave you sucking wind. After a few weeks, you'll notice that the same amount of exercise won't leave you quite as breathless, and your heart won't thump quite as loudly. That's a sure sign of progress, but it's also a sure sign you need to kick into a higher gear. In fact, there's some scientific evidence to suggest that doing one or two hard-hitting workout sessions a week can rev up weight loss; when you push yourself, you burn a greater number of calories per hour and can pump up your resting calorie burn rate for several hours -- or even several days -- afterwards. For stalled weight-loss efforts, add one to two weekly "interval training" workouts (that's where you mix speedy, high-intensity intervals lasting one to five minutes with slower recovery intervals lasting an equal amount of time).

Go Longer: There is no question that some exercise is better than none at all. However, when you're attempting to downsize, 20 minutes here or there probably isn't going to cut it. According to many expert organizations, there's a certain calorie burning threshold you need to hit to begin making a dent in excess body fat. For example, the American College of Sports Medicine proposes shooting for 300 calories worth of exercise daily. The National Weight Control Registry recommends burning 2,800 calories per week through exercise, which translates into four to seven hours of movement depending on your mode of exercise, how intense your workouts are and how much you weigh.

Balance it: A combination of aerobics, weights and mind-body activities will help you get there faster. Aerobic pursuits, such as running, cycling and swimming, burn tons of calories but don't do much for your metabolism. Weight training burns some calories, but its main purpose is to build and preserve fast metabolizing muscle. Stretching, whether it's traditional, Yogic or Pilates-based, burns more calories still and keeps your muscles supple and injury free so you're less likely to miss a workout.

Diet matters: It takes about 14 minutes of moderately-paced walking to burn off 100 calories and about a millisecond to scarf down 100 calories worth of chocolate. Even though research indicates that exercise is the most important health habit you can cultivate for both losing and maintaining weight loss, all the treadmill sessions in the world won't do you any good if the majority of your meals consist of super-sized portions of junk food. That doesn't mean jumping on the latest fad diet bandwagon. However, you're probably going to have to limit calories to some extent, even if you're religious about working out.