Biomechanics and Medicine in Swimming XI

that the cause that the body weight could not be supported by the leg
because θ_take-off was about 2º lower than θ_before.
There were a few influences of the back plate at take-off and during
flight phase. The important aspect was that swimmers could improve
with any technique with some intensive practice (Sanders & Bonnar,
2008). As subjects did not have an enough skill for using a back plate yet,
they could not keep the domination on the starting block.
conclusIon
In conclusion, the influences of the back plate to competitive swimming
starting motion in particular projection skill were identified as follows:
(1) At the set position, the centre of mass displaced to a comparatively
anterior position; (2) The rear leg knee joint angle at the set position
was set at about 90º; (3) Just before take-off, the body was accelerated
into the horizontal direction; (4) At take-off, the projection angle could
be kept nearer the horizontal. For a fast start, it is suggested that some
intensive practice make best using of these advantages on the starting
block.
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AcKnoWledGeMents
This study was supported by The Grant in Aid for Scientific Research
(C) 20500543 of Japan Society for the Promotion Science.
chaPter2.Biomechanics
Kinematical Characterisation of a Basic Head-out
Aquatic Exercise during an Incremental Protocol
oliveira, c. 1,4 , teixeira, G. 1,4 , costa, M.J. 2,4 , Marinho, d.A. 3,4 ,
silva, A.J. 1,4 , Barbosa, t.M. 2,4
1University of Trás-os-Montes and Alto Douro, Vila Real, Portugal
2Polytechnic Institute of Bragança, Bragança, Portugal
3University of Beira Interior, Covilhã, Portugal
4Research Centre in Sports, Health and Human Development, Vila Real,
Portugal
The aim of this study was to analyze the relationships between musical
cadence and kinematical characteristics of a basic head-out aquatic exercise,
when immersed to the breast. Six young women with at least one year
of experience conducting head-out aquatic classes were videotaped in the
sagital plane with a pair of cameras providing a dual projection from both
above and underwater performing 5 incremental bouts (120 b.min -1 , 135
b.min -1 , 150 b.min -1 , 165 b.min -1 and 180 b.min -1 ) of the basic head-out
aquatic exercise “rocking horse”. There was a decrease of the cycle period
throughout the incremental protocol. Relationships between horizontal
or vertical displacements with music cadence were not significant. On the
other hand, increased cadence imposed increased segmental and centre of
mass’ velocities. As a conclusion expert and fit subjects seem to increase
segmental velocity with increasing musical cadence to avoid the decrease of
the segmental range of motion.
Key words: head-out aquatic exercises, rocking horse, musical cadence,
kinematics
IntroductIon
Massive research has been produced throughout the last decades in order
to better understand the role of head-out aquatic exercises in populations’
health (Barbosa et al, 2009a). Indeed, such studies aimed to characterize the
physiological acute and/or chronic response of subjects performing headout
aquatic exercises. Moreover, the comprehensive knowledge about the
biomechanical (i.e. kinematical) behavior performing this aquatic activity
is quite reduced.
Conducting head-out aquatic exercise sessions, instructors often use
the music cadence to achieve a pre-imposed intensity of exertion. Music
cadences between 130 and 150 b.min -1 are suggested by technical literature
for head-out aquatic exercises (Kinder and See, 1992). At least one empirical
study reported that for healthy and physically active subjects instructors
should choose music cadences between 136 and 158 b.min -1 (Barbosa et
al., 2009b).
Increases in the music cadence imposes significant increases in the acute
physiological adaptation (e.g., rate of perceived effort, heart rate or blood
lactate) of the subjects (Hoshijima et al., 1999; Barbosa et al., 2009b). It
is hypothesized that increased physiological response may be explained by
the fact that increasing music cadence will also increase movement velocity
and frequency, decreasing the segmental range of motion. However, to
our knowledge there is no study in the literature reporting the kinematical
changes imposed by an incremental cadence protocol at head-out aquatic
exercises.
The aim of this study was to analyze the relationships between musical
cadence and kinematical characteristics of a basic head-out aquatic exercise,
when immersed to the xiphoid process (i.e., breast).
Methods
Six non-pregnant, clinically healthy and physically active young women
holding a graduation degree in Sports Sciences and at least one year of
experience conducting head-out aquatic classes volunteered to participate
in this study (23.67 ± 0.52 y-old; 57.42 ± 4.78 kg of body mass; 1.64 ± 0.07
m of height; 22.17 ± 2.56 kg.m -2 of body mass index).
137