A previous study showed that adult female dancers have a high percenta
ge of type I fibres in vastus lateralis. similar to that of endurance-
trained female runners or female cross-country skiers. It is not known
if dancers already at an early age are characterized by a high percen
tage of type I fibres or develop a high percentage or type I fibres as
a consequence of dance training. Furthermore. the muscle fibre compos
ition of male dancers has not previously been studied. Therefore the a
im of the study was to analyse skeletal muscle fibre characteristics i
n 10-year-old and 20-year-old dancers of both sexes. Age-matched boys
and girls whose physical activity was average for their age groups ser
ved as controls. Muscle biopsies for histochemical analysis were obtai
ned from vastus lateralis using the percutaneous needle technique. The
major finding of the present study was that the vastus lateralis of y
oung dancers of both sexes had a higher percentage of type I fibres th
an that of controls. Moreover. the higher type I percentage was seen n
ot only in 20 year olds, but also in 10 year olds, who had begun their
dance training at a professional level only a few weeks earlier. No s
ignificant difference in this respect was found between Female and mal
e dancers. In conclusion. the muscle fibre type composition in young d
ancers of both sexes differs from that of the average individual of th
e same age and is characterized by a high percentage of type I fibres.