Anyone can call herself a personal trainer even if -- literally -- she doesn't know her deltoids from her from her derriere. That's because the term personal trainer has no more legal meaning than the terms personal chef or personal shopper. Theoretically, there are no requirements or skills essential to becoming a personal trainer other than the ability to print up business cards or advertise in the local penny saver. So who can you trust to tone your biceps and buff your abs safely and effectively?

Certification is one of the few generally accepted personal training qualifications. But with more than 300 personal trainer certifications being offered, it requires a certain amount of savvy to decipher what's relevant and what's not worth the paper its written on. Use this information along with the person's background, education, personality and work experience to make an informed decision regarding your personal trainer's certification credentials.

Go with the big three: At the very least, your trainer should be certified by one of the three major personal training organizations: the American College of Sports Medicine (ACSM), The American Council on Exercise (ACE) and the National Strength and Conditioning Association (NSCA). These three are widely accepted as the most professional and trustworthy certifying organizations. ACSM certified trainers are tested on understanding medical history, fitness testing, determining fitness level and creating exercise routines appropriate for each exerciser. ACE exams emphasize creating well-rounded programs for a variety of clients including athletes, older people or those with orthopedic problems. NSCA exams focus largely on understanding anatomy and weightlifting technique.