The Dancer
Physical Effort, Muscle Fibre Types, and Energy Intake and Expenditure
Monica Dahlström
From Karolinska Institutet, Department of Medical Laboratory Sciences and
Technology,
Division of Clinical Physiology, Huddinge University Hospital, Huddinge,
Sweden.
The aims of this thesis were:
-to estimate aerobic fitness in dancers and analyse possible changes
during a three-year dance
course and after a detraining period.
-to compare different dance styles with regard to the duration of single
exercises and the
following rest periods.
-to estimate the physical effort in dancers during training sessions in
different styles of dance.
-to compare the physical effort during training sessions in dance
teachers with that of dance
students.
-to illuminate whether a deviating muscle fibre type distribution, if
any, were training-induced
or the result of selection of individuals with suitable fibre
characteristics, muscle fibre type
distribution was compared between children, at the very beginning of
their professional dance
training and dancers, who had performed professional dance training for
10 years. Moreover,
muscle fibre type composition was analysed in dancers after detraining.
-to investigate the dietary habits of female dancers and to compare the
estimated daily energy
intake (Ein) with the estimated daily energy expenditure (Eexp) and to
explore whether a
discrepancy found in female dance students between estimated daily Ein
and estimated daily
Eexp could be explained by a depressed basal energy expenditure (BMR).
Results and conclusions:
The estimated maximal oxygen uptake (VO2max) in the dance teachers and
the dance students
was 20-30% higher than in a randomly selected population with average
physical activity. This
and the 20% increase of estimated VO2max in the students over the
three-year dance course
indicate that dance training implies rather high demands on the
cardiovascular system.
Dance training is a predominantly intermittent type of exercise of brief
active and rest periods.
This concerns classical ballet as well as other dances styles as modern
dance, jazz dance and
character dance.
The physical effort expressed as heart rate (HR) in % of maximal HR was
approximately 70%
for both teachers and students with no difference between the dance
styles. This would
correspond to a perceived exertion of "somewhat hard" to "hard" The blood
lactate
concentration indicates a moderate activation of the anaerobic energy
production during dance
training.
Muscle fibre type composition in young dancers, even at the very
beginning of their
professional dance training, differs from that in the average individual
and is characterised by a
high % of type I fibres, similar to that found in 20 years old dancers.
This, together with the
fact that detraining did not change the muscle fibre type composition,
supports the idea that the
high percentage of type I fibres in dancers is due to a selection of
individuals with suitable
muscle fibre composition to the dance profession rather than being an
effect of training.
The 20% higher estimated daily Eexp than daily Ein as found in the dance
students and no
change in body weight over a six month period suggest that the Eexp was
overestimated or the
Ein was underestimated. In our estimation of daily Eexp a normal BMR was
assumed. If the
BMR had been lower than expected this would have led to an overestimation
of the daily Eexp.
In a subsequent study a normal BMR was demonstrated in the dance
students. Thus, no
support was found for a depressed BMR in the dancers, which consequently
cannot contribute
to explain the apparent discrepancy between daily Eexp and daily Ein.
This may underline the
uncertainty of dietary surveys, when applied to groups engaged in extreme
physical activity as
also pointed out by others.
Key words: Children, dance, diet, exercise, exertion, female, fitness,
muscle.
ISBN 91-628-2205-