What it is: High-intensity interval training technique, usually 30 minutes including warmup and cooldown. It sharply increases strength, endurance and fat loss by pushing muscles to exhaustion, with short rests. For 4 minutes, student performs 20 seconds of intense workout, then 10 seconds of rest, repeats seven times, rests a full minute, then begins the next workout routine.

Who it is for: Classes typically offered to intermediate or advanced students 15 and older, and children 10 or older with an adult. Some centers offer special classes for ages 5 and older.

Where it is offered: Many YMCA, YWCA, CrossFit, Life Time Fitness and other centers. A range of DVD and online programs, such as Insanity and P90X, use Tabata techniques and are sold online at and other websites. Some local groups using DVDs organize informally through Facebook or Meetup.

What it costs: Classes often free for fitness center members. DVD programs cost $120 and up.

The risks: Without instructors, beginners and some advanced athletes may push too hard, injuring joints, backs or muscles. Intensity can be scaled to fit the student.