You can’t use exercise to target specific areas (so sit-ups won’t give you a flat stomach)

TRUE “Sit-ups will strengthen your core, but they won’t get rid of belly fat,” says Daniel Lieberman, a Harvard University paleoanthropologist and the author of Exercised: the Science of Physical Activity, Rest and Health. “The good news is that we evolved to carry belly fat as a short-term energy supply, so when you start losing weight through exercise, that’s the first fat that’s going to get burned.”

According to Nick Finney, a personal trainer whose clients include Jennifer Lopez and Robbie Williams: “In order to lose weight, you need a prolonged calories deficit, which you get by eating less and exercising more. You’ll lose more belly fat doing compound exercises – deadlifts or squats – rather than targeted exercises like sit-ups, because they burn way more calories.”

Sore muscles are the sign of a successful workout

FALSE “You can have a great workout without any soreness,” says Finney. “Delayed onset muscle soreness (Doms) is usually just a sign of surprise – so people often find they are sore after their first few trips to the gym, or after trying a completely different workout, or a much longer one. There are some muscles, like biceps, which will hardly ever get sore – but that doesn’t mean that working them out hasn’t been successful.”

You should always stretch before and after exercise

FALSE “Hundred of studies have looked at whether stretching reduces the risk of injury during exercise,” says Alex Hutchinson, author of Which Comes First, Cardio or Weights? Fitness Myths, Training Truths, and Other Surprising Discoveries from the Science of Exercise. “The overall conclusion is that if there’s an effect, it’s too small to measure consistently. People often conflate stretching with warming up. Starting any bout of exercise with some gentle movement – it can be as simple as a light jog – will bring your body temperature up and make your muscles more supple. But that warm-up doesn’t need to include stretching.”

You shouldn’t work out with a bad back

FALSE “Traditionally, the advice was to avoid certain exercises (for instance, deadlifts or barbell rows) if you had a bad back, but theories have changed,” says Finney. “Obviously if you slipped a disc yesterday, you’ll want to recover and rehabilitate it, but after that initial recovery period, a lot of workouts will strengthen the back. If you aren’t injured but have an everyday bad back, movement is medicine – you should 100% be working out. If you never exercise the back muscles, they’ll become weak, which will leave you more vulnerable to injury.”

You should aim to walk 10,000 steps a day

TRUE “The first company that produced pedometers came up with the 10,000-step benchmark without any data, as that was considered an auspicious number,” says Lieberman. “Since then, plenty of studies have shown that steps a day is a reasonable way of measuring physical activity. As you increase your step count, you reap increased benefits, but it tails off between about 8,000 and 10,000.”

Hutchinson agrees: “There’s nothing magic about 10,000 steps a day, but it is pretty good advice. In general, the best target is probably ‘a little more’ than what you’re currently doing.’’

Muscles will turn to fat if you stop working out

FALSE “They are two completely different tissues – muscle doesn’t turn to fat and fat doesn’t turn to muscle,” says Sarah Lindsay (@roarfitnessgirl), a three-time speed skate Olympian and owner of Roar Fitness. “If you stop exercising and eat more calories, you will gain fat. If you stop stimulating your muscles, you will lose muscle mass.”

Finney adds: “The confusion comes when people who are seriously active and used to eating a lot stop training or become injured. If they carry on eating the same amount and stop resistance training, their muscles will decrease and their fat will increase – but one won’t turn into the other.”

Running is bad for your knees

FALSE “If knees were like the shock absorbers on your car, it would make sense to avoid wearing them out through overuse,” says Hutchinson. “But knees are a living part of your body that respond and adapt to regular use. Underusing them is bad for the cartilage. So when researchers follow comparable groups of runners and non-runners over many decades, they find that the runners are no more likely to develop knee problems than the non-runners. That doesn’t mean no runner will ever develop knee problems, but it does mean that running isn’t worsening your odds.”

Lifting weights will make you bulky

FALSE “Gaining muscle is really hard,” says Finney. “On top of lifting increasingly heavy weights, you have to be in a calorie surplus (eating more calories than you are burning). It isn’t going to happen by accident. Some people avoid weightlifting because they are wary of gaining too much bulk, but if you are trying to lose weight, lifting weights while in a calorie deficit is a good way to do it (and will ensure that you burn fat rather than muscle). Plus, the stronger you are, the heavier you lift, so the more calories you burn.”

The more you exercise, the better

FALSE “Recovery and rest are really important,” says Lindsay. “If you do one class in the morning and another at lunchtime, you probably won’t train very well in the second session. Training more and more will just mean that you’re really tired and unable to create any intensity.”

Finney suggests: “A good benchmark to see results is three workouts a week, with a rest day between each.”

Yoga gives you a flat bum

FALSE “Yoga won’t build your glutes,” says Finney. “It’s difficult to stimulate the building of muscle with body weight alone – you need progressive overload, which means lifting more this week than the week before. But doing yoga won’t decrease your glutes either, so there’s no reason it should give you a flat bum.”

Evening exercise will stop you getting to sleep

TRUE and FALSE “Exercise is a stimulus, which elevates level of cortisol – an arousal hormone which is the enemy of sleep,” says Lieberman. “For most people, exercising right before you go to sleep is not going to work.” According to Finney, “Everyone is different – exercising before bedtime will stop some people from getting to sleep, but others use it to tire themselves out. You have to find what works for you and your routine.”

You should consume protein within half an hour of a workout

FALSE “The theory goes that you have an anabolic window in which to absorb protein after a workout,” says Finney. “But really, your total day consumption is the most important thing. If you want to build muscle, you should be aiming to eat 2g of protein for every kilogram that you weigh.”

Lindsay adds: “This is more applicable for carbohydrates. Your ability to store carbohydrates in the muscles as glycogen – a glucose which can be used as energy later – peaks after training, so that’s a good time to eat carbs. You do also need to consume protein, but you won’t be able to digest chicken immediately after a workout because your blood isn’t in your stomach – it has been diverted to your lungs and muscles. Straight after a workout is a good time for liquid nutrition, like protein shakes.”

Metabolism decreases with age

TRUE and FALSE

“Your metabolism does decrease,” says Lindsay, “but not until you are about 65 or 70. Really what reduces your metabolism is lack of muscle – and muscle mass does reduce with age for lots of different reasons. This is why I encourage people to hold on to every pound of muscle they can – it will keep your metabolism up and makes sure that you remain strong as you age.”

You should switch routines to avoid a plateau

FALSE “People tend to switch their routine too much, perhaps because they get bored,” says Finney. “But if you want to improve at anything, you have to practise. For instance, a pull-up is brilliant at building your back and biceps, and burns a lot of calories – so if you want to do those things, it’s better to get great at pull-ups than to constantly try different exercises and never get proficient. It takes time and practice to cultivate good technique in the gym, so you’re better off focusing on the fundamentals than switching every week. A good fitness regime includes resistance training, cardio and mobility work, but switching routines too often won’t allow you to get better at the fundamentals of any of them.”

Sex is good exercise

TRUE and FALSE According to Lindsay: “If you’re trying to do cardio and elevate your heart rate, I don’t care how you do it (although the heart rate monitor might be a bit of a mood killer). It’s all good – whether you want to dance, or shag, or cycle, it doesn’t really matter.”

However, Hutchinson suggests managing expectations. “Research suggests that ‘active, vigorous’ sex burns 2.8 Mets [metabolic equivalent of task], meaning you’re burning 2.8 times more energy than you would just lying on the sofa,” he says. “For comparison, playing a trombone takes 3.5 Mets. Running at 10-minute-mile pace burns about 10 Mets. It’s better than nothing, but you’d have to rack up an awful lot of minutes in bed to move the needle as exercise.”

You shouldn’t work out when you’re ill

TRUE “If you’re ill, your immune system is busy trying to fight the illness,” says Finney. “Working out also compromises the immune system, so doing both at once risks making you more ill or prolonging the illness. It’s better to take a couple of days off exercise than to put your immune system under unnecessary strain.”

Hiit is the most efficient way to exercise

TRUE and FALSE “Lots of people do high-intensity interval training as a quick way to burn fat,” says Lindsay. “But by definition, Hiit is high intensity – so your heart rate will be too high to burn fat [your fat-burning heart rate is at about 70% of your maximum heart rate]. Another problem is that inexperienced people aren’t strong or powerful enough to create a lot of intensity, so they just end up doing a very short workout.”

However, “Hiit is a good way to burn a lot of calories in a short amount of time,” according to Finney. “Ideally you’d also be lifting weights, which builds muscle, so increasing your metabolism while at rest [because muscle burns three times as many calories as fat when at rest].”

Exercise is more important as you age

TRUE “Exercise stresses the body, which activates repair and maintenance mechanisms, which in turn wipe up damage and keep us healthy,” says Lieberman. “It produces antioxidants, which repair DNA damage; it reduces inflammation, which is the cause of most diseases; it produces brain-derived neurotrophic factor, which helps prevent Alzheimer’s. Study after study shows that exercise slows senescence, the deterioration associated with age – so exercise becomes more, not less, important as you get older.”