If you believe running is bad for the knees or that yoga helps a sore back, think again, reports The Guardian. Working-out can not only be tough and time-consuming, it is often downright bamboozling. Listen to all the advice about which sort of exercise to choose and you might be excused for wanting to hang up your sweats in despair. To simplify gym matters, let’s see how the five biggest fitness myths stack up against scientific fact.

Myth: You can spot-reduce fat from any part of the body

The diet and fitness industries have traded for so long on the concept of targeting specific body parts for fat removal - hip-and-thigh eating plans, bums, tums and thighs work-outs, - that quite a few people have actually come to believe that spot-reduction is possible. But scientific studies cast considerable doubt on the possibility of selectively taking weight off the waist, thighs or buttocks.

Dr. Cedric Bryant, chief science officer for the American Council on Exercise, a consumer watchdog for the fitness industry, says there is little evidence to support such claims. One landmark study designed to test the spot-reduction theory was carried out at the University of Massachusetts, where 13 male subjects did a vigorous abdominal exercise program for one month.

Each subject performed a total of 5000 sit-ups over 27 days. But when fat biopsies from their stomachs, buttocks and upper backs obtained at the beginning and end of the trial were analysed, fat loss proved similar at all three sites, not just the abdomen.

“If caloric expenditure is enough, it will cause fat from the entire body, including that from a target area, to be reduced,” Bryant says. “However, although fat is lost from the entire body through exercise and calorie reduction, it appears that the last areas to become lean tend to be those areas where an individual tends to gain fat first. For most men, that is the abdominal region and for women it is hips, buttocks and thighs.”

Myth: Running is bad for your knees

Slapping the pavement with the soles of your runners has gained a reputation as hazardous to the knee joint. But a recent study showed that running actually protects those joints from damage and pain.

Reported in the journal Arthritis Research and Therapy, a team from the Department of Immunology and Rheumatology at Stanford University in southern California found that adults who run consistently can expect to have 25 per cent less musculoskeletal pain and less arthritis when they get older than non-runners.

Dr Bonnie Bruce, the study’s author, followed more than 500 runners from a local club (called “ever runners” in the study) and 300 inactive people (“never runners” though not necessarily sedentary) in their 50s and 60s for 14 years.

When results from an annual health questionnaire were analysed, Bruce and her colleagues found that the ever runners, who ran at least six hours per week on average, experienced less joint pain by their 60s and 70s and only 35 per cent of the joggers got arthritis (compared with 43 per cent of non-runners).

Sammy Margo, a sports physiotherapist for the Chartered Society of Physiotherapy, says running doesn’t deserve its bad press.

“The key is consistency,” Margo says. “If you run consistently, your joints, tendons, ligaments, disks and muscles get used to the habitual pounding of the activity. The body accommodates and copes with the demands.”

It is the yo-yo runners, says Margo, who take up jogging and then drop it repeatedly over a number of years who might have problems down the road.

Myth: Pilates will give you a celebrity body

Fans are reported to include Madonna, Jodie Foster and Liz Hurley, but while the cult gym practice might leave you with a super-strong core or middle-section, it will do little to improve your cardiovascular fitness or lower-body fat, at least according to the results of a study last year by the American Council on Exercise (ACE). Professor John Pocari and his team of exercise scientists at the University of Wisconsin analysed the demands of 50-minute beginner and advanced-level Pilates classes and found the intensity of each to be lower than the recommended level for improving cardiovascular fitness.

In the beginner classes, the maximum heart rate of the healthy and moderately fit female subjects was only 54 per cent when the accepted range for boosting fitness is 64-94 per cent. They burned 175 calories. Even the advanced class failed to raise heart rates above an average 62 per cent and burned only 254 calories, equivalent to the benefits gained from walking at a slow pace. In order to get fitter and slimmer, the experts suggested that Pilates be done in conjunction with aerobic activities such as running or cycling. “Pilates has a long list of benefits including improved body mechanics, balance, co-ordination, strength and flexibility,” says Dr Cedric Bryant of ACE. “A Pilates session burns a relatively small amount of calories, but it is still a valuable addition to an exercise routine.”

Myth: Yoga is good for back pain

Contorting yourself like a pretzel on a yoga mat may be good for many things but not, apparently, for your back. In a study published in the Annals of Internal Medicine, researchers found that a gentle yoga class seemed a better alternative to “either general exercise or a self-help book” for back pain. However, Dr. Karen Sherman, who conducted the study, conceded that more vigorous types of yoga, such as ashtanga, and classes led by poorly qualified instructors, could potentially make problems worse. Matt Todman, consultant physiotherapist at the Sports and Spinal Clinic in London, goes further, saying “yoga is generally not good for back pain and a lot of its postures can compound the problem by loading pressure on the back”.

Staying active, though, is important, although back-pain sufferers should do so only on the advice of their physiotherapist. Jeremy Fairbank, consultant orthopaedic surgeon at Nuffield Hospital, Oxford, found that patients obtain as much benefit from an intense program of exercise therapy as from spinal surgery.

Fairbank’s trial, involving almost 350 patients, revealed that those who followed a tailored daily exercise program involving step-ups, treadmill walking, cycling and core stability work for five days over three weeks made huge progress.

Myth: You don’t need to “feel the burn” to get fitter

Current recommendations suggest that totting up half an hour of activity by performing tasks such as housework, gardening or collecting the newspaper is enough to ward off heart disease and keep us healthy. But these are minimum requirements (even though many barely manage to meet them) and if you really want to shape up, it requires a lot more sweat and toil.

Research by the American College of Sports Medicine (ACSM) sets what are widely regarded as the core targets of exercising: three to five times a week for 20 to 60 minutes at 55-90 per cent of your body’s maximum capacity, calculated according to your heart rate, if you want to improve fitness. “That constitutes a fairly vigorous work-out that would leave you breathless and puffing,” says Dr Greg Whyte, sports science co-ordinator for the English Institute of Sport. “And it is the level you need to be doing if you want to get fitter.” That doesn’t mean we can rest on our laurels for the rest of the time. Whyte believes too many people have “reached a point where they think going to the gym three times a week is enough”. But, he says, while working out will contribute considerably towards overall fitness, “there are 23 and a bit hours remaining in the day and we should try to be active at least during some of them”.