Ever spent hours pounding away on a treadmill, then coming to the end of the week and finding your weight hasn't shifted at all?
Or how about eating cake in the knowledge you'd been for a long cycle ride, yet somehow piling on the pounds? You're not alone - or going mad. You've simply fallen foul of something scientists are increasingly recognising: exercise often doesn't help you lose weight. And worse yet, there's increasing evidence that it could even make you fatter. Just last month, in an article for the British Journal Of Sports Medicine, doctors said we have wrongly emphasised that physical activity can prevent people becoming very overweight.
The truth, they said, is that while physical activity is useful in reducing the risk of disease, it "does not promote weight loss". That false perception, they claimed, "is rooted in the food industry's public relations machine, which uses tactics chillingly similar to big tobacco companies - denial, doubt and confusing the public".
In addition, the Mayo Clinic, an eminent medical research group in the US, says studies "have demonstrated no or modest weight loss with exercise alone" and that "an exercise regime is unlikely to result in short-term weight loss".
Here are the reasons why your gym membership isn't giving you the whittled waist you want...
You reward yourself without realising
There are a lot of conflicting reports about the effects of exercise on appetite. We're all familiar with the idea of going for a walk to work up an appetite, but most research seems to suggest that exercise doesn't necessarily make us eat more. Rather, it can make us eat the wrong things.
The post-workout bar of chocolate to celebrate a job well done - or even a healthy banana - can undo all your good work without you realising.
This is known as 'compensation' by sports scientists: a person who exercises cancels out the calories they have burned by eating more, generally as a form of self-reward.
This was demonstrated in a recent study by Arizona State University, which focused on the effects of exercise on 81 overweight women with sedentary lifestyles. The researchers asked them to participate in a 12-week exercise programme involving three treadmill sessions a week. They were told to follow their usual diet.
The research found that while they were fitter, there was no noticeable weight loss and 70 per cent of the women had piled on some fat.
While the study didn't track the women's eating and movement habits away from the lab, it is likely that those who gained weight began eating more and moving less when they weren't on the treadmills - "probably without meaning to", say the scientists.
Obesity researcher Zoe Harcombe believes that exercise has a psychological affect on what and how much we eat. "Exercise is seen as being deserving of a reward," she says. "WeightWatchers even builds the concept into their programmes, giving you extra points for exercise. But, all too often, the treat that people reward themselves with is out of proportion to the amount of exercise they've done."
Study after study has shown that we're notoriously bad at estimating the number - and type - of calories we've consumed.
One, which looked at more than 5,000 adults, found the participants under-estimated their consumption of fats, oils and sweets, and overestimated how much fruit and protein they'd eaten. By the same token, most of us woefully underestimate how much exercise we need to offset indulgences.
The other issue is that, even if you did nothing, your body would be burning calories. For example, a 10 st person just lying watching TV for an hour will burn about 70 calories. But exercise machines show you the total number of calories burnt - what your body is expending on its own and the extra you're burning while doing exercise.
The rowing machine may tell you you've burned 250 calories for an hour's work, but you've actually 'earned' only a 180-calorie reward.
So if you reward your 20-minute run (218 calories expended, but actually only 148 extra calories) with a latte (180 calories), you're, in fact, taking on more calories than if you hadn't exercised.
Multiply that on a weekly basis, and you can see how things get difficult.
Stress is sabotaging you
We're often told exercise is the solution to stress, but it actually releases the fight or flight hormone cortisol - also known as the stress hormone. If our bodies are functioning properly, most of this cortisol is offset by endorphins, or anti-stress chemicals, the body also produces during exercise. However, according to personal trainer Janey Holliday (makingthingseasy.com), if you're already stressed and your hormonal system isn't working as it should be, that excess cortisol won't be efficiently offset, leading to even more of the stress hormone in your body.
"Cortisol is bad news for anyone wanting to lose weight," says Janey. "Research shows that high levels of cortisol cause the body to hold onto fat and boost appetite."
Worse yet, cortisol encourages fat to be stored around the middle, and it's known that fat in this area is associated with an increased risk of heart disease, diabetes and breast cancer.
"If you're stressed and want to lose weight, you might be far better off working on improving your sleep and relaxing by doing a bit of power walking, rather than throwing yourself into a punishing routine," adds Janey.
Danger of secret calories
Are you the type of person who swears they just can't shift the pounds? Annoyingly, there's probably something in it.
A recent review of studies related to exercise and weight found that people lost barely a third as many pounds as would have been expected, given how many calories they were burning during workouts. Many studies also report enormous variations in how people's waistlines respond to the same exercise programme, with some dropping pounds and others gaining fat.
The latest trend for High Intensity Interval Training (HIIT) where you exercise intensively for short bursts with short recovery in between is said to burn as many as 12 calories in a minute.
That might sound impressive, but the standard 20-minute workout will only just cover a large glass of wine, and even the fittest people would struggle to do the three back-to-back workouts that half a bottle of wine, a shared pack of Kettle Chips and a handful of olives would require.
Crucially, when you've started exercising, you need to keep it up - one US study suggested that weight gained after stopping exercise can be tough to shed when exercise is resumed. And once you've reached your goal weight, it's a lot of work to stay there.
Eating like an athlete is bad for you
If you take an energy drink to the gym, or carb-load on a Friday in preparation for your Saturday morning run, that might be where you're going wrong. Thanks to health magazines and the internet, it's easy to find information that may work for pro-athletes, but is actually unhealthy for the rest of us.
"I've lost count of the number of fitness fanatics I have tried to help with weight problems, only to be told that they have to 'carb-load', or that they must have sports drinks, or gels, or snack bars," says Zoe Harcombe. "Actually, they need none of these. They're full of calories, and fattening."
A report from Powerade, one of the leading sports drink brands, even advises that only athletes who are doing multiple, high-intensity training sessions, lasting longer than 60 minutes need extra fuel.
So while triathletes or marathon runners might need gels, power bars, and plates piled with pasta to get them through, for the rest of us, they're just extra energy that could mean we're piling on the pounds.
You always do the same type of exercise
We've all heard people enthuse about the fact that they embarked on a new gym regime and the pounds just fell off. But those pounds don't keep on just falling off.
Scientists at the University of Tampa in Florida found that what they called 'low-intensity steady state cardio' - something like running on a treadmill for about 45 minutes at a steady pace, or using an elliptical trainer for a long period of time - did result in initial weight loss, but that after a few weeks, subjects stopped losing weight. They believe that this is because the body adapts and becomes more efficient, so the same exercise requires less effort.
In fact, experts believe that if you're trying to lose weight by combining a low-calorie diet with a lengthy cardio workout, you're heading for disaster.
This is because not only does your body adapt so you have to do more to get the same result, but as low-calorie diets tend to be low in carbohydrate, once you've used up any carbohydrate stored in the muscle, the body starts to use the muscle itself for energy. So, not only are you not losing fat, you're losing muscle mass.
And, if you're trying to lose weight, the last thing you want to do is lose muscle mass. That's because while we think that we expend most of our calories when we're exercising, most of our energy is used up just existing - even if you did nothing for 24 hours, you'd still be burning nearly 1,700 calories in a day - and the more muscle mass we have, the more calories we burn.
Which exercise is best?
Which brings us neatly to the type of exercise you should be doing to lose weight. Anything that builds muscle is, for the reasons above, a good thing when it comes to weight loss - so resistance training should be a part of your workout.
And although cardio exercise has a role to play, the way most of us run - or cycle, or row - isn't doing us any favours. We tend to work at a relatively low intensity so we can keep it up for about half an hour, whereas what we should be doing is short, sharp bursts of exercise at maximum intensity, and then recovering for a shorter period of time - without the rewards afterwards.
Research from the University of Western Ontario compared a group of people doing short intense exercise with another group who were running at a steady pace for between half an hour and an hour three times a week.
After six weeks, all the exercisers had improved in a number of areas but, crucially, the sprinters had on average reduced their fat mass by 12.4 per cent with the distance runners only 5.4 per cent.
Exercise might not guarantee weight loss, but some is better than none.
It's good for your health
A review of research found that exercise is associated with a diminished risk of a number of conditions, including cancer, heart disease, dementia, stroke, type 2 diabetes, depression, obesity and high blood pressure.
It gives you time to yourself
"A walk, a swim or a run can be a real opportunity to escape from your busy life and spend some time reflecting," says personal trainer Janey Holliday. And while a workout in a busy gym may not seem like time on your own, it's still the chance to focus entirely on you, your body and what it needs.
It can be a lot of fun
There are so many different types of exercise that there's bound to be one you enjoy. Whether it's the more meditative yoga and pilates-style classes, dance-based aerobics, or kickboxing, find something you genuinely want to do and make sure it fits easily into your daily routine.
- Daily Mail