Biomechanics and Medicine in Swimming XI

The Effect of a Target Sound Made by a Model
Swimmer’s Dolphin Kick Movement on Another
Swimmer’s Dolphin Kick Performance
shimojo, h. 1 , Ichikawa, h. 2 , tsubakimoto, s. 1 , takagi, h. 1
1 Graduate School of Comprehensive Human Sciences, University of Tsukuba,
Tsukuba City, Japan
2 Department of Sports Information, Japan Institute of Sports Sciences, Tokyo,
Japan
The aim of this study was to determine the effect of a target sound made
by a model swimmer’s dolphin kick movement on another swimmer’s
dolphin kick performance. Fifteen competitive swimmers participated
in this study. Subjects were required to swim using a dolphin kick while
listening to the target sound as closely as possible. The aim of the task
was to determine whether the timing and displacement of their dolphin
kick would change, and the degree to which the change would
be retained without the sound. After swimming with sound, subjects
experienced a decrease in timing error relative to their performance
without sound for up to 300 s, but displacement error did not decrease
significantly. The results also suggested that with auditory models, which
have been particularly effective for timing patterns, it would be hard to
recognize displacement differences.
Key words: dolphin kick, motor learning, auditory model
IntroductIon
In swimming training, the swimmer must enhance power and endurance
for good performance, which involves efficient movement. Such
high performance movement must be achieved through effective motor
learning.
Many motor learning and motor control studies were conducted in
sports psychology and neuroscience. Target tracking tasks, require the
subject to move a cursor utilizing a mouse to track moving target point
on display. The trajectory error of trials was used to evaluate performance.
Yamamoto et al. (2007) reported target tracking tasks utilizing an auditory
model, where the movement target on display was synchronized
with stereo sounds expressing right or left by sound volume control. The
subject was required to control the mouse to get close to the moving target
following auditory model with the eyes closed. They suggested that
the auditory model could be used in real world sports training.
Baudry et al. (2006) reported that an auditory concurrent feedback
on cyclic movement was effective in motor learning and performance.
Wang and Hart (2005) reported that an auditory model that was an
effective method to enhance the learning of swimming movement timing
in beginner classes. But an auditory model has not been attempted
in expert swimmers. If an auditory model could affect motor learning
to create the skilled movement required for high performance in competitive
swimming, coaches and swimmers could use such a method to
enable swimmers to improve each other’s performance in training. The
purpose of this study, therefore, was to determine the effect of a target
sound produced by a model swimmer’s dolphin kick movement on another
swimmer’s dolphin kick performance.
Method
Fifteen competitive swimmers (ten males and five females) participated
in this study. They were aged 22.1 ± 4.7 years and all subjects had more
than ten years of experience in competitive swimming and had normal
hearing. An informed consent was obtained from all subjects before
their participation in this study.
Before this study, one model swimmer swam with the dolphin kick
in the pool at sub-maximal speed (1 m/s) for getting two-dimensional
coordinates by filming. After a single kick phase was chosen, coordinates
chaPter5.education,adviceandBiofeedBack
of the swimmer’s vertical range were exchanged to relative coordinates
(% height). We created a “target sound” that indicating displacement
differences expressed as sound frequency scales in the range of 300~900
Hz converted by the coordinates. Because “Concert A” or “Middle A” is
the 440 Hz tone that serves as the standard for musical pitch and is used
in instrument tuning, the range of 300~900 Hz was adopted with an
average of 440Hz for the “target sound”. Prior to this study, it had been
confirmed whether the model swimmer could replay the same movement
while listening to the target sound in the pretest.
After it was explained to subjects what the target sound indicated,
the subjects were required to swim with the dolphin kick after a wall
push start to a distance of 10m while listening to the target sound, and
to “track” the target swimmer’s movement. The task was to swim “tracking”
the movement of the target as well as possible. After the normal
dolphin kick test that required the subject to swim at 80 % or less effort,
there were two tasks. The aim of Task 1 was to see whether difference of
sound scale would affect the displacement of a swimmer’s dolphin kick.
The 75% range (375~825 Hz) and the 50% range (450~750 Hz) target
sound, indicating that the height of toe displacement in the dolphin kick
was narrow, were obtained from the target sound. Task 1 was conducted
the 75% and the 50% target sound were used randomly for ten trials,
and the effect was investigated from differences between pre 1 and post
1 trials with target sound.
The aim of Task 2 was to see whether the swimmer’s dolphin kick
would retain any improvements without the target sound. Task 2 was
conducted with the target sound for ten sessions. The effect was investigated
from differences between pre2, post2, post3 (60 s later), post4 (120
s later) and post5 (300 s later) with no sound requiring the subjects to
reproduce the same dolphin kick movement as in Task 1. Figure 1 shows
the study protocol.
Figure 1. Protocol followed in which subjects were required to use the
dolphin kick in every trial.
Data collection was undertaken in an indoor swimming pool whose
depth ranged 1.3 m to 1.8 m. Every trial was recorded using four cameras
(TK-C1381 Victor Inc., Japan) through an underwater poolside
window. Data sampling set 60 Hz. The two-dimensional coordinates
of the swimmers’ vertical toe displacement were obtained by a two-dimensional
DLT method using motion analysis software (Frame-DIAS
4, DKH Inc., Japan), and were exchanged to relative coordinates (%
height) for comparison with the model swimmer. The sound was generated
utilizing underwater speakers (MT-70 Toyoonkyo Corp., Japan)
that were synchronized with the underwater cameras. Figure 2 shows
the evaluation from data collected.
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