Exercise classes have made an evolutionary leap since the early 1980s, when crinkle-leather Reebok shoes and leg warmers were de rigueur. Back then, "aerobics" meant two hours of sadistic military drills -- and a steady stream of casualties from the ultra-deep knee bends, jerky moves and high kicks considered criminal today.

Classes are better now because clubs and aerobics studios generally require their instructors to have experience and certification. Many clubs audition teachers, do regular evaluations and pay attention to participant feedback. But you still have to be on the lookout for instructors who are nothing more than "diva duds." You know the type: Their routines are more showy than safe, their style more effusive than effective.

Regardless of whether your thing is low impact, spinning or the Funky Diva Workout, use the following checklist to help you determine if your instructor makes the grade.

• Is she certified by a nationally recognized organization such as the American Council on Exercise or the American Fitness Aerobics Association?
  Give her bonus points for: Having a degree in exercise science or certification to teach spinning, yoga or other specialty classes.
• Is she certified in CPR?
  Give her bonus points for: First aid certification.
• Does she ask about medical conditions or past injuries at the beginning of the class?
  Give her bonus points for: Giving special attention to first time class takers.
• Does she modify the class intensity for different levels of students and encourage everyone to work at their own levels?
  Give her bonus points for: Offering specific tips for those with back, knee, neck and shoulder injuries.
• Does she demonstrate and enforce safe, effective technique?
  Give her bonus points for: Explaining the purpose or benefit of each move.
• Can you hear her over the music?
  Give her bonus points for: Using a microphone and keeping the music at a decibel level that doesn't make your ears pound.