Every woman, and the few men who have tried, know Step aerobics is about much more than keeping fit. Intellectually it's on a par with studying for an advanced degree in nuclear physics.
Linguist Judy Delin, of Sterling University, spent seven years deciphering the arcane language of the aerobics instructor. She says under-standing it is one of the most taxing mental challenges of the modern world.
Dr Delin, whose research will be published later this year, painstakingly transcribed tapes of aerobics lessons to unravel how people interpret the baffling stream of commands and visual signals.
In one lesson, the instructor shouted 500 orders and words of encouragement in 28 minutes. Dr Delin says the words - or "utterances" - are meaningless unless you know the subtle series of codes, delays and timings that make routines work. She believes the enormous mental challenge to keep going without falling over is probably the root of aerobics' popularity.
The fact that for Step one needs a big brain could explain why it is the most popular sport for women - but of no great attraction to men.