Scientific studies of the legs of female professional dancers have revealed a shocking truth: they have the same percentage of slow-twitch muscle fibres as top-level female runners or cross country skiers. This is extremely surprising, since professional dancing involves speed, power, and agility rather than the ability to plod along for extended periods of time.

In an attempt to figure out why dancers' legs have so many slow-twitch muscle cells, Swedish researchers recently biopsied the leg muscles of young (10-years old) and 'old' (19 years) dancers. Surprisingly, both young and old dancers had the same percentage of slow-twitch fibres (some scientists had speculated that the high amount of effort associated with dancing workouts gradually transformed dancers' fast-twitch muscles into slow models, accounting for the high proportion of slow-twitch fibres in experienced dancers), and dancers had considerably more slow-twitch cells compared to 'normal,' non-dancing individuals in the overall population (62 per cent slow-twitch in dancers versus 55 per cent for the 'man or woman on the street').

The study is interesting because it suggests that dance training doesn't change the composition of dancers' leg muscles. Instead, individuals with high er percentages of slow-twitch fibres - and therefore greater endurance and a heightened ability to withstand long training sessions - are drawn to dance as a sport. In addition to suggesting that muscle composition influences an individual's selection of a sporting activity, the Swedish investigation indicates that many competitive dancers would make excellent endurance athletes.

('Is Dance Training In Childhood Related to Deviating Skeletal Muscle Characteristics as Estimated by Biopsies?' Biochemistry of Exercise Ninth International Conference Abstract, #18, p. 18,1994)