Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
Effects of Reduced Knee-bend on 100 Butterfly
Performance: A Case Study Using the Men’s Asian
and Japanese Record Holder
Ide, t. 1 , Yoshimura, Y. 2 , Kawamoto, K. 3 , takise, s. 1 , Kawakami,
t. 1
1 Osaka University of Health and Sport Sciences, Osaka, Japan.
2 Chuo University, Tokyo, Japan.
3 Phoenix Swim Club, Phoenix, Arizona, USA
This article analyzed the 30 year old Asian and Japanese record holder
of the men’s 100 meter butterfly. In 2002, Kohei Kawamoto’s best time
was 53.22 seconds, and he improved his time to 51.00 seconds in 2009.
The most significant difference between Kohei in 2002 and 2009 was
the focus on a straight leg butterfly kick technique. When comparing
his 2005 stroke to his 2009 stroke, we found that the extent of the
straightness of his butterfly kick improved from 39% to 55% (of >170
degrees knee-bending). Additionally, this swimmer improved his speed
from 2.5m·s -1 to 2.7m·s -1 , and increased his distance per stroke from
1.894m±0.062 to 2.204m±0.131.
Key words: training, Asian and Japanese national record,
Butterfly, straight kick, coaching, swimming speed Meter.
IntroductIon
Butterfly swimmers should keep their body as horizontal as possible
during the propulsive phase of the arm stroke (Maglischo, 2003). In
general, coaches use the technique of ‘wave butterfly’ ( Japan Swimming
Federation, 2006), and the dolphin kick technique of bending the knees.
The wave butterfly arises from body movement, arm-stroke timing and
kick timing (Yoshimura, 1996). Bending the knees during the butterfly
kick increases the undulation of ‘wave butterfly’. Coaches still use the
technique of bending the knees during the butterfly kick, with the purpose
of pushing back the water (Fig.2).
Since 2006, we coached Kawamoto to change his butterfly technique,
employing a straighter leg-kick. The result was a more horizontal
stroke. Kawamoto’s initial butterfly kick technique used a bending butterfly
kick. We changed this to a straighter kick with less knee-bend
(Yoshimura, 2008), which is imagined as ‘holding the water to the bottom
the pool’ (Fig. 1).
Figure 1. Straight kick.
270
Figure 2. Bending kick.
Methods
Kohei Kawamoto, 30 years old Asian and Japanese record holder of the
men’s 100 meter butterfly (height; 174 cm, body weight; 64kg) volunteered
to participate in this study. A comparison was made of Kawamoto’s
performance in 2009 to his previous performance in 2005. He
performed 4 times 25 meter butterfly swims, whilst being filmed, from
a push start. The first 15 meters were completed under water using the
butterfly kick and the final 10 meters swimming all out butterfly stroke.
A Swimming Speed Meter (Vine, VMS-003, AC100V, 1/500s, 0.2mm/
pulse) using a wire attached to the swimmer, exported the analogue signals
via an RS232C post to a computer. These signals were used to calculate
swimming speed (Microsoft Windows Excel; Yoshimura, 2007).
The wire line of the speed meter was attached to the swimmer by a
belt and intracyclic velocity changes were recorded precisely for several
stroke cycles while swimming at maximum speed. The average velocity
changes for one stroke cycle were calculated with data from all successive
stroke curves. The average number of stroke cycles were compared
(for the 2009 stroke and 2005 stroke). A Swimming Speed Meter, registered
velocity when the subject was at maximum speed within one
stroke cycle, which is during the second kick phase. Then comes the
wave phase, and first kick phase, insweep phase. During swimming, the
subject was monitored from the side plane using an underwater video
camera at a sampling frequency of 60Hz (Underwater monitor system
2, YAMAHA, Shizuoka, Japan). The angle of the knee bend and upper
body movement. were analyzed with the DartTrainer.
results
The Swimming Speed Meter showed that swimming speeds increased
from 2.5m·s -1 for 2005 to 2.7m·s -1 in 2009 (during the second kick
phase). Distance per stroke (DPS) increased to 2.204m±0.131 for 2009,
from 1.894m±0.062 in 2005 (m) Wicoxon.: p=0.006061, 1 stroke (velocity)
Wicoxon.: p=0.7748) (Figure 3.). Four phases of the 2009 and
2005’s velocity results were not significantly different (the first kick
phase Wilcoxon: p=0.64850, insweep phase Wilcoxon: p=0.16360, upsweep
and second kick phase Wilcoxon: p=0.00606, wave phase Wilcoxon:
0.10910.