Speed fluctuation as a determinant factor of energy cost in Butterfly stroke
Conference Paper
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abstract
The purpose of this study was to examine the relationships
between the speed fluctuation of the centre of mass and the
EC, in butterfly stroke.
Five national level Portuguese swimmers performed one
maximal and two sub-maximal (85% and 75%) 200-m butterfly
swims in a 25-m swimming pool. Cardio-pulmonary and gas
exchange parameters were measured breath by breath for each
swim to analyze VO2 and other energetic parameters by
portable metabolic cart (K4b2, Cosmed, Rome, Italy). A
respiratory snorkel and valve system with low hydrodynamic
resistance was used to measure pulmonary ventilation and to
collect breathing air samples. Blood samples from the ear lobe
were collected before and after each swim to analyze blood
lactate concentration (YSI 1500L, Yellow Springs, US). Total
energy expenditure (È-tot) and EC were calculated for each
swim. The swims were videotaped (50 Hz) in sagital plane with
a set of two cameras providing dual-media images from both
underwater and above the water surface. The cameras were
real time synchronised and the images were edited on a mixing
table to create one single image of dual-media. APAS system
(Ariel Dynamics Inc, USA) was used to analyse speed
fluctuation for the centre of mass. Coefficients of variation for
the horizontal velocity of the centre of mass along the stroke
cycle (dV) were calculated. Linear regressions between the
bioenergetic and biomechanical variables were computed, as
well as, its 0.05). Coefficients of determination and correlation
(p).
There was a significant and linear relationship between È-tot
and velocity (r=0.827, p=0.0005). Statistically significant
correlation coefficient between the EC and the dV (r=0.807,
p=0.0009) was found, the coefficient of determination being
r2=0.651. This means that the increase in the EC being strongly
associated with the increase in the speed fluctuation. The
individual coefficients of correlation and determination between
the EC and the dV were very high (mean r2 0.018, ranging from
0.973 to 1.000). The mean of individual correlation È= 0.986
0.009 coefficients was higher than the overall correlation
coefficient (r=0.993 vs r=0.807) of the pooled data.
It is concluded that the speed fluctuation of the centre of mass
was related to less efficient swimming and vice versa in
butterfly. We suggest that the swimmers should strive to
improve their technique performances by avoiding large
variations in the speed fluctuation.
