If you enjoy keeping fit, make a living out of it by studying to be a personal trainer

The image of a personal trainer as a Lycra-clad athlete poised to run a marathon isn't so far off the mark if Jenny Burrell is anything to go by. The 37-year-old freelance fitness instructor, from Maida Vale, west London, admits to spending most of her waking life in tracksuit bottoms and a polo shirt.

But away from the gym and there's more to Burrell's job than Speedos and sweat pants. She sees sensitivity to her clients' needs – not to mention their physiological limitations – as far more important than attaining physical perfection herself.

"I provide training in everything from posture to diet, and I'm very goal-orientated, tailoring my approach to each individual," says Jenny, a specialist in antenatal and postnatal programmes. "I might have an American football player in the morning lifting weights, and a heavily pregnant woman in the afternoon."

Indeed, if current industry estimates are to be believed, it's not just Beyoncé and Britney Spears who've caught the physical training bug: everyone's at it. The National Register of Exercise Professionals (REP), which accredits qualified professionals, boasts 24,000 active members, and rising. At least one in four is a personal trainer, and of those three-quarters are successfully self-employed.

The escalating popularity of personal training is reflected in the fees. While there are bespoke fitness programmes to suit most budgets these days, experienced practitioners like Burrell can command anything up to £50 an hour.

So how does one become a personal trainer? For Burrell, it was a matter of falling into the job by accident. "I have a degree in biochemistry and microbiology, but after finishing university I joined a pop group," she says. "As I neared my 30th birthday, I thought to myself, 'I don't really want to be gigging any more'.

"I'd been going to the gym for a while and the guys there said, 'you come here so often, you should be paid to', so I decided to look into what it would take to become an instructor and found it wasn't going to be as hard as getting my biochemistry degree."

Jenny studied for an RSA certificate in teaching exercise to music (aerobics to you and me), followed by a YMCA qualification in gym instruction. From there, she moved to a more specific NVQ in personal training – regarded as the industry gold standard, and a requirement for registration by REP.

The ease with which she qualified was matched by the modest expense of launching her business. She took out a £12,000 loan, two-thirds of which paid for equipment – essentially a "gym-level" treadmill, weights and exercise bikes.

Her biggest outlays since have been the £100 a year she spends insuring herself against third-party injury and the continuing professional development she has to undertake to maintain her registered status.

While it's possible to qualify as an instructor by taking an evening course, new degrees are emerging all the time for those interested in combining vocational training with academic disciplines like physiology. Last autumn, The University of Bedfordshire launched a BSc in exercise and fitness, incorporating conventional sports science modules with the personal training NVQ.

"Other universities expect students to do a three-year degree, then go out and spend another £3,000 to get the extra qualification in personal training," says lecturer Kevin Wyld. "We deliberately embedded it in our degree to avoid them having to do that."

A demonstrable advantage of the more practical aspects of this BSc is that it equips undergraduates to obtain work in the industry while studying – enabling them to finance their course using skills they have acquired through it. By the time they complete their first year, most are already qualified to work as paid gym instructors.

One second-year student already putting his studies to profitable use is Darren Player, 19. He says: "I've been doing some performance analysis for Bedford Rugby Club, which involves watching their matches on video and studying how they tackle and so on, with a view to improving their game. I'm getting paid, and I'll also be allowed to use the data for my dissertation, so it'll help my academic work too."

For details of approved personal training courses, go to the REP website at www.exerciseprofessionals.com