By Dorene Internicola

NEW YORK, July 22 (Reuters) - If you're spending more time running, walking or pumping iron in the gym and still not losing weight, fitness experts say it could be due to too big a reward for still too little exercise.

Although fitness has indisputable health benefits, it takes a lot of walking or running to burn off the calories in a donut.

"There's a war between exercise and nutrition in our heads," said American Council on Exercise spokesperson Jonathan Ross. "People tend to overestimate the amount of physical activity they get. They work out a little bit and treat themselves a lot."

A report by the University of Washington's Institute for Health Metrics and Evaluation showed that although Americans say they are more active, it has not made much of a dent in the obesity epidemic that affects more than one-third of U.S. adults.

Ross, a personal trainer based outside Washington, D.C., said exercise can play a role in weight reduction, but without broader lifestyle and nutritional changes, that role is limited.

"We put exercise in a box and once that exercise box is filled in we don't do much the rest of the day," he explained, adding that a post-workout calorie-dense treat doesn't help.

"Some (weight-loss) programs stress nutrition, some stress exercise," he said. "But the two together are greater than the parts."

The National Weight Control Registry, which gathers information from people who have successfully lost at least 30 pounds (13 kilos) and kept it off for a least one year, reports that 90 percent of its members exercise, on average, about one hour per day.

U.S. health officials recommend that healthy adults get at least 150 minutes of moderate-intensity physical activity a week, or around 20 minutes a day.

Dr. Joseph E. Donnelly, an exercise physiologist with the American College of Sports Medicine said the U.S. government guidelines are for cardio vascular fitness, not weight loss.

"It was never intended for weight management," said Donnelly, a researcher who focuses on obesity at the University of Kansas. "People have misused it."

He added that studies suggest 250 to 300 minutes of exercise per week may be the minimum to lose weight.

"At 150 (minutes) the best you can hope for is weight maintenance."

Donnelly said if there's a success story for the role of exercise in weight control, it's in maintenance.

"Even among the naysayers who feel you can't lose much weight through exercise, most people agree it seems important to maintain weight," he said.

Dr. Michele Olson, professor of exercise physiology at Auburn University Montgomery, in Alabama, said it is difficult to shed pounds through exercise alone.

"One pound of fat has 3,500 calories," she explained. "If you ran a 26-mile marathon, where you burn about 100 calories per mile, you would burn 2600 calories, falling 900 calories short of burning one pound of fat."

She added that people must be physically active regardless of their size or whether they are losing weight.

"Moderately intense exercise done in as few as 10-minute increments two to three times a day markedly reduces our risk of all causes of mortality, heart disease most effectively but all other causes, including cancers, deaths due to hypertension and strokes, etc.," she said.

Ross said for many of his clients the goal is to maintain vitality and capability.

"For anyone out there who is frustrated about not losing weight, try to focus instead on what you love about your life," he said. "The No. 1 goal is to feel better in your body. That's what exercising is good for." (Editing by Patricia Reaney and Andrew Hay)

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  • Running Right

    Most runners have a love-hate relationship with the treadmill. On the one hand, it's boring and <a href="http://www.huffingtonpost.com/2013/03/07/gym-germ-hot-spots_n_2814171.html" target="_hplink">germ-infested</a>. On the other, it's often a necessary evil to get through long winters or rainy mornings. <a href="http://www.huffingtonpost.com/2012/06/23/outdoor-exercise-health-benefits_n_1616467.html" target="_hplink">Working out outside has noted benefits</a> over hitting the gym, including improved energy and a greater likelihood to <em>keep</em> exercising. But in case you're stuck inside, we want to make sure you're doing it right. We asked three fitness experts -- personal trainer <a href="http://www.huffingtonpost.com/matthew-basso/" target="_hplink">Matthew Basso</a>, president of Iron Lotus Personal Training; <a href="http://www.RunCoachJason.com" target="_hplink">Jason Karp</a>, Ph.D., an exercise physiologist and the author of Running for Women and Running a Marathon For Dummies and <a href="http://cardiellofitness.com/" target="_hplink">Jay Cardiello</a>, celebrity trainer, author and creator of JCore -- to share their biggest treadmill pet peeves. Here are some of the most common mistakes they see gymgoers make, and what we should be doing instead.

  • You Crane Your Neck To Watch TV (Or Your Feet)

    Anything that throws off your posture, whether it be hunching over to watch your feet or leaning to the left for a better view of the TV, is generally a bad idea. "Your neck is pulled to the right or dropped forward and one part of the musculature is getting stretched while another is getting tightened," says Basso. The longer you're in that position, the higher your risk of injury becomes, he says. You're also likely to offset your balance, warns Karp. "You're looking to the left or to the right and your body's going to follow a little bit," he says. Slumping over can also limit your oxygen intake, says Cardiello. To guarantee you're standing your tallest, imagine someone is pouring ice water down your spine, he says. For those runners who rely on a little screen time at the gym, try to find a treadmill with a screen attached, says Cardiello, so you can face forward with your chin parallel to the ground. If your gym isn't equipped with those machines, head to the back of the room. That will keep your neck as straight as possible while still allowing you to watch overhead TVs, he says. "Keep your head, heart and hips inline when you run," he says. "You're running <em>over</em> the ground, never into the ground." Or the belt, as the case may be.

  • You're Too Zoned Out

    Clearing your mind with your favorite TV show during your run is one thing. Jumping on the treadmill with concrete fitness goals is another. "I think a lot of people who choose to use cardio equipment, yeah, they sweat, but your mind starts to wander," says Basso. "Instead of really being present and focusing on the exercise, your gait, your posture, people lose it there." A too-engrossing book or magazine, or a movie might be too distracting, says Cardiello. "Save the reading for your cooldown."

  • You Do The Same Thing Over And Over

    "One of the biggest mistakes people make [at the gym] is to do the exact same thing every time, and then wonder why they don't see results," says Karp. So shake things up, by varying the intensity, speed or incline. Try a longer and slower run one day, and a shorter and faster one on another visit, he says. A great way to mix things up <em>and</em> see results sooner is with an interval workout, says Cardiello. <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2991639/" target="_hplink">Short bursts of higher intensity exercise</a> can up the fat-burning powers of your workouts, improve heart health and more, not to mention save you some time. And you might also want to consider adding in a little sideways movement, says Basso. Unless you're really coordinated, don't attempt to walk backwards or do anything too fancy on a treadmill. But most people -- at a slow pace -- can handle some lateral shuffling or crossover steps, he says, to work yours muscles in different ways.

  • You Skip The Warmup

    Yes, you're busy. Some days you just want to hop on the treadmill, get it over with and get out. But skipping a warmup can lead to pain and injuries, says Basso. You don't need a lot of time, and you don't need to passively stretch, he says. Instead, take five to seven minutes for an active warmup with a "joint-by-joint approach," he says, that includes hip circles, toe touches and more. "It's more of a priority to keep your mobility and keep yourself out of pain than to start a workout," he says.

  • You Hold The Bars

    Holding onto the handrails on the treadmill might seem like a safety measure, but your workout will suffer, says Karp. Some of your bodyweight will be supported, meaning you won't have to work as hard and you won't burn as many calories, he explains. If you feel like you need to hold on, it's probably because you're going at a slightly faster speed than you're ready for, he says. "Get comfortable without holding on in increments to gain confidence at each speed," he suggests.

  • You Set The Incline Too Steep

    How often do you encounter a steep hill in the outside world that takes you an hour to climb? Exactly. Exercise should be <em>functional</em>, says Basso, and strengthen your muscles for real-world use. Plus, the steeper that incline, the more likely you'll be holding onto the bar to keep yourself on the belt. "If you have to hold on, it's either too fast or too steep," says Karp.

  • You Trust The Settings

    Between the heart-rate monitor grips on the handrail and the button for the "fat-burning" zone, there's not much worth trusting on that digital dashboard. "You can't really rely on those," says Karp. "The mathematical formulas are rough estimates based on a lot of variables," he says. And every runner is different. Since they're probably not accurate to begin with, says Cardiello, don't obsess over the numbers on your machine. "Throw a towel over the display," he says, and you might just find you work a little harder.

  • You Jump Off With The Belt Moving At Full Speed

    It might seem like taking a water break without slowing down the belt saves you time in the longrun, but not if it makes you trip and fall first. "Most people don't have the coordination to do that without risking injury," says Karp. "I see people all the time who come close to falling." Fess up, are you guilty of any of these? Did we miss any common mistakes you see at the gym? Let us know in the comments!