Maybe it is boredom with the navel gazing of yoga or the repetition of Spinning, but gym-goers, it seems, are turning their backs on the latest crazes preferring to pull on their legwarmers for old-fashioned aerobics classes instead. The fitness phenomenon of the Eighties had all but died out by the late Nineties. But in a trend that is winging its way around the globe from the United States, it's back.
"People are definitely rediscovering the enjoyment of choreographed exercise classes to music," says Howard de Souza, a spokesman for the Fitness Industry Association. "Classes do come in and out of fashion and people get bored with what they are doing and want to try something else, so aerobics was bound to have a second life. At the moment updated versions of it are creeping onto timetables everywhere."
The dance element of aerobics helps to boost its appeal with many gym-goers bored with the rigidity and repetition of such classes as Pilates. Instead, they want to have fun, says Louise Sutton, the head of the Carnegie Centre for Sports Performance and Well-being at Leeds Metropolitan University, who has been observing the trend. Aerobics classes are also the fastest route to all-round fitness. Typically, an hour-long session involves jumping, sidestepping, kicking and the classic aerobics step, the "grapevine", to throbbing music, with sections devoted to toning and stretching. Aerobics can burn more than 450 calories an hour - the equivalent of running for the same amount of time - and will work all the major muscles in the body, unlike running and cycling. It is undoubtedly beneficial for cardiovascular health and for strengthening bones, thereby protecting against osteoporosis.
But for all its retro appeal, some experts are concerned that the return of aerobics could herald a sharp rise in exercise-related injuries. Thanks to their high-impact nature, aerobics steps send a shock equivalent to eight times your body weight reverberating up your legs and into your spine, more than is encountered during running or classes such as Boxercise. "It is particularly risky to the kneecap, unstable joints, and to people with weak backs and posture problems. If you dive into doing a high-impact class, your ankles and hips could also be vulnerable to injury," says Kirsten Lord, a spokesperson for the Chartered Society of Physiotherapy based in London.
Some of the associated risks include plantar fasciitis, a pain in the arch of the foot caused by too much stress on the feet, shin splints - painful inflammation of the shin muscles and tendons due to the pounding - and, most commonly, stress fractures to the feet. Indeed, many of the original devotees are still living with the consequences of their exertions. "In the 1980s a lot of people did aerobics on hard floors without realising the damage they were doing," says Jay Blahnik, a spokesperson for the IDEA Health and Fitness Association, an international trade body. "If they were doing a few classes a week back then, the chances are that they will have problems now. Many instructors and participants I have come across can't do jumping whatsoever anymore because they have pain in their backs, hips, legs and feet."
The term "aerobics" was coined by a former US Air Force surgeon Dr Kenneth Cooper in a fitness book he wrote in 1968. It describes activity that works the body's aerobic systems, including the heart and lungs, to the full, as opposed to the intense muscular work of anaerobic activity such as sprinting and weightlifting. A decade later the actress Jane Fonda popularised the concept with her work-out books and videos.
Before Fonda opened her first aerobics studio in 1979, gyms had been almost exclusively the domain of bodybuilders, boxers and athletes. As the trend for group exercise classes soared, Jane Fonda's Workout became one of the best-selling videotapes in history. In fact, Fonda and the aerobic movement are widely credited with triggering the growth of gym culture. Unfortunately, another legacy of the 1980s aerobics fad was a catalogue of injuries to instructors and participants.
American research carried out in 1985, the heyday of aerobics, showed that 76 per cent of those taking part experienced some form of injury such as sprained ankles, back pain, Achilles tendon strain and heel spurs (a build-up of calcium deposits on the underside of the heel bone) as a result of regular classes. A study by experts at the Department of Physical Education and Sport Science at the University of Thrace in Greece, where classes remain popular, found that almost 60 per cent of aerobics instructors suffer overuse injuries, such as stress fractures, serious enough for them to abstain from teaching for at least a month at a time.
Researchers at the Hospital for Special Surgery in New York also found that the approach causes severe muscle tears or bone fractures. "We often see people with injuries from high-impact aerobics classes," says Dr Jordan Metzl, a sports- medicine specialist at the institution. "Sometimes they are acute injuries, the sort you might get in any class, but usually they are from overuse and too much pounding."
Dr Kalpesh Parmar is a specialist sports-medicine practitioner who trained at the Australian Institute of Sport and now counts top footballers and athletes among his clients. He warns that too many high-impact classes can have devastating effects on your joints. "When people start doing three or more classes a week, that can lead to overuse injuries such as stress fractures, cartilage tears and shin splints," he says. "If they continue to do all that pounding for a number of years, the knee in particular takes a hammering and arthritis of that joint can be common."
Step aerobics, popularised in the 1990s by the American fitness guru Gin Miller and also coming back into fashion now, has attracted similar criticism. Like aerobics, it is set to music but requires jumping, stepping or hopping on and off a raised platform. A report by the American Academy of Podiatric Sports Medicine found that many injuries are the result of the step being too high and from too much bouncing off the platform, placing force on the legs which causes forefoot injuries, metatarsalgia (toe joint inflammation) and stress fractures.
Bridgitte Swales, a personal trainer and lecturer in sport and exercise science at Roehampton University in London, says that while aerobics can be damaging, it is not entirely bad. The way it is performed is what puts people at risk. "With anything that is repetitive and puts the joints under persistent high impact, there is a risk of problems for some people," she says. "If you run every day with bad shoes that have no cushioning or side-to-side support for the foot and have poor technique, you are likely to get injured. In fact, if people have underlying problems and use poor technique, then any type of vigorous exercise can be potentially harmful."
Swales adds that today's participants have better facilities to protect against some of the dangers of aerobics. "The fitness industry is a lot better informed than it was 30 years ago. Back then, a lot of aerobics classes were held in crowded rooms on unsprung floors which compounded the shock through the legs and spine. Now, gym flooring has a lot more give and shock-absorption," she says. Improvements in footwear should also offer more protection from the shock previously transmitted to the 26 bones of the foot, says Lord. "For aerobics, you need specialist shoes that provide cushioning and support for side-to-side motion as well as for twisting and turning - running shoes won't do," she explains. "And make sure you attend a class where the instructor can see what you are doing, as bad technique will almost certainly lead to problems."
However, Sutton says that, with caution and a well-run class, aerobics can be a fun part of a fitness programme once or twice a week. "But it should not be your only means of getting fit," she says. "Do that and you could be in trouble."