Truth about fitness: Will those sit-ups ever pay off?

Can sit-ups help me to get a flat stomach?

This is perhaps the most popular myth I have to deal with. By performing sit-ups or "crunches", you are helping to strengthen and firm up the rectus abdominus muscles, more commonly known as the "six-pack". But crunches will do nothing to reduce the amount of fat you have on your tummy. Abdominal fat is there because of excessive calorie consumption, so the only way to get rid of it is to burn off the calories by following a balanced diet and performing high-intensity exercise such as running, cycling, aerobics and swimming.

However, there is one trick that can help to give the appearance of a flatter stomach. Underneath the rectus abdominus lies a band of muscle called the transversus abdominus. Also referred to as the "corset muscle", the transversus abdominus helps to keep the back strong and compresses the abdomen. Exercising this muscle regularly can help to improve your posture and make the stomach appear flatter.

Suck in your stomach, so that your belly button is drawn towards your spine. While the stomach is sucked in, do not hold your breath, just keep breathing normally. You will know you are doing this properly when you begin to feel a minor burning sensation in the deep stomach. Once you've mastered it (the breathing can take some practice), you can do this exercise anywhere and it will help to flatten your stomach and improve your posture.

I've been running three miles three times a week, so why are my fitness and weight just the same?

In the early stages of a running regime, the improvements are encouraging. New runners who stick to their three miles, three times a week regime see a dramatic improvement in fitness levels and weight loss. Accompanied by a firmer bum and fewer flabby bits, the incentive to carry on is obvious.

But despondency can set in after a few months when the improvements seem to slow down. An exercise regime has to change if you want your fitness levels to keep improving and your wobbly bits to continue to disappear. The body adapts to anything you throw at it, and once it becomes accustomed to a certain intensity and regularity of exercise, improvements tend to plateau. If you want to keep on improving your rate of fitness and fat loss, you have to continue to up the intensity to avoid a plateau, a process referred to as "overload". You can increase the intensity either by running faster, further, up a hill or more often.

If I exercise my tricep muscles, will I lose my "bingo wings"?

The tricep muscle on the back of the upper arm is an area where many women of a certain age begin to accumulate a little more fat than they feel is acceptable. The misconceptions on how to make them disappear are rife.

Using exercises to target specific muscle groups such as the "nanna wobbles" can help to a degree by firming and toning up the muscles, but sadly it is a myth that exercising a certain area will encourage the fat to melt away. This theory of "spot reduction" has been tested numerous times on tennis players, comparing their racket arm with the other one. Although there was a clear musculature difference between the two, fat levels were identical, proving that exercising a particular muscle does not reduce its fat content unfortunately!

Is BMI a good way of determining whether I'm overweight?

The Body Mass Index (BMI) is used by many GPs to determine whether a patient is overweight. The trouble with this method, according to many health professionals, is that it is very dated and out of touch with the variety of readily available and modern forms of body-composition tests.

Your BMI is your weight (in kilograms) divided by your height (in metres) squared. Less than 18.5 is considered underweight; a healthy weight is 19.0 to 24.9; 25.0 to 29.9 is overweight; and over 30 is obese. So, to take me as an example, 85kg is divided by 1.83 x 1.83 metres. This gives a BMI of 25.3. So, according to the BMI, in spite of the fact that I am a personal trainer, exercise four or five days a week and follow a healthy diet, a doctor could interpret this reading as a sign that I'm getting a little porky and should think about shedding a few pounds.

True obesity levels should not be determined by the scales, but by how much excess body fat you carry. As a regular exerciser, I am lucky to have a low level of body fat (less than 12 per cent)) and a fairly bulky musculature, but according to the BMI system I am verging on unhealthy.

Many GPs would argue that it is a quick and easy way to inform some people that they are overweight and need to adjust their lifestyle. But it is far from perfect. Due to the lower muscle mass of women, BMI is slightly more accurate for them than for men but, unless you know that you're excessively overweight, you should take your BMI reading with a pinch of salt and get your body fat measured as well.

Which burns more calories, running a mile or walking a mile?

The answer is more complicated than you might think. Studies carried out by the exercise physiologists Jack Wilmore and David Costill suggest that a 70kg man will burn five calories a minute walking at 3.5mph and 18.2 calories a minute running at 10mph. To save you the maths, per mile that equates to 85 calories expended in a one-mile walk and 109 in a one-mile run. So is the extra effort of running really worth it?

The answer is a resounding "yes". At rest, even though the body is inactive, it still requires energy to sustain basic cellular and physiological functions such as brain activity, heart rate and enzyme reactions. Known as our Basal Metabolic Rate (BMR), the resting human body expends anywhere between 1,200 calories and 2,400 calories a day, depending on sex, age and genetics. However, when daily activity such as a walk or a run is added, our BMR is increased to anywhere between 1,800 and 3,000 calories.

Our BMR is also determined by how active our muscle tissue is. If our muscles are exercised thoroughly, as they are during a run, their need for energy at rest to help replenish expended nutrients is greatly increased. It is believed that, after a hard run, the energy demands of the leg muscles are doubled for up to 48 hours. Although a walk will elevate the resting energy requirements of muscles to a degree, it is incomparable to a run.

Am I too old to go running?

Age does not necessarily have to be a barrier when it comes to running. Look at Leslie Chapman, the oldest man to compete in the 2006 London Marathon, who finished in seven hours, 16 minutes and 39 seconds at the age of 84.

Running may not appeal to all pensioners, but in your later years it can be not only safe but also a highly effective way to keep your heart and bones strong. It also helps to lower cholesterol, maintain strength and combat cardiovascular disease and osteoporosis.

As we age, our joints can start to cause us problems, but not all people will suffer from degenerating joints. Exercise of any kind, not just running, in your later years has to be enjoyable, practical and above all safe. Irrespective of whether you have been running all your life, or whether you fancy taking it up in your forties, fifties or sixties, provided that your doctor has given you the all clear and you are able to run pain-free, there's no reason why your age should stop you.

Is there a regime that will slim down my hips and thighs?

Any food-supplement company, personal trainer or herbalist who tells you that certain foods and exercises can help to disperse the accumulation of fat on the hips and legs of women is either lying or grossly misinformed. Poor diet and no exercise is the reason why some people accumulate fat. Also, the fluctuating hormones of the female body are responsible for the unwanted dumping of fat at a number of sites on the body. At the centre of this hormonal roller-coaster is oestrogen, which is responsible for a number of feminine characteristics, such as wide hips, breast development and the dreaded depositing of fat, especially on the hips and thighs.

An enzyme called lipoprotein lipase is at the root of this, and the reason so many women fight a losing battle when it comes to fat on the hips and thighs. Made in the fat cells, lipoprotein lipase blocks the ability of the body to transport fat to be used as energy. Therefore, wherever the activity of the lipoprotein lipase is high, you will find an excessive amount of fat. Unfortunately for women, the high activity of lipoprotein lipase and a low degree of lipolysis (fat breakdown) in these areas makes the fat incredibly difficult to shift, and this is one of those facts of life some women have to accept.

For the lucky few who have very little lipoprotein lipase activity in their thighs (especially men), I wouldn't brag about it. Although men may possess very little lipoprotein lipase, they are more prone to the effects of a stress hormone called cortisol, which is responsible for depositing fat on the stomach.

Is It Just Me Or Are Sit-ups a Waste of Time? by Graeme Hilditch is published by Metro (7.99). To order your copy (free P&P), call Independent Books Direct on 0870 079 8897