Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
conclusIon
By using EMG amplitude and frequency analysis, the progression of
muscle fatigue in arm propelling muscles was clearly detected. No differences
in the relative decrease of MNF between the muscles under
observation were found. This suggests that these muscles fatigued to
approximately the same extent during all-out crawl, which may present
significant information for the coaches in order to plan strength
workouts.
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170
Comparison Among Three Types of Relay Starts in
Competitive Swimming
takeda, t. 1 , takagi, h. 1 , tsubakimoto, s. 1
1 University of Tsukuba, Tsukuba, JAPAN
The purpose of the present study was to evaluate the effectiveness of
no-step, single-step and double-step relay starts for swimmers. Eight
male collegiate swimmers participated in the present study. For each
type of start, each swimmer performed six trials of relay starts with maximum
effort. Ground reaction forces were measured using a Kistler
force plate to calculate the take-off velocity and take-off angle
from the force data. Relay times were measured by counting the
number of video frames obtained by a high-speed camera. No
significant difference in the horizontal take-off velocity was observed.
The relay times decreased significantly in the order nostep,
single-step and double-step starts (P < 0.05). Eight trials
among all the trials for the step starts resulted in incorrect foot
placement on the edge of the block. No-step starts resulted in
better performance than step starts.
Key words: step start, relay time, performance
IntroductIon
In relay events, it is possible to record a time on the starting block (block
time) of zero second. The block time is the time that elapses between
the instant at which the start signal is given and the instant at which
the swimmer’s foot leaves the starting block. In relay events, the first
swimmer begins the race when the start signal is given, and swimmers
to follow start after the previous swimmer has reached his or her finishing
point. Therefore, the time on the block of the swimmers to follow
should ideally correspond to the instant at which the previous swimmer
reaches his or her finishing point. The block time of an individual in
regular events ranges from approximately 0.6 to 0.8 s, as reported in
previous studies (Issurin & Verbitsky 2003, Takeda & Nomura 2006).
The results of relay events depend upon the technique adopted while
changing swimmers during a relay. The sum of the block times in the
three changeover swimmers represents approximately 2.4 s.
There are two kinds of starting techniques in relay events. Their
starts generate greater horizontal velocity upon take-off from the starting
block (McLean et al. 2000). The swing start involves the swing of
an arm. On the other hand, the step start involves taking one or two
steps before jumping with both feet from the block. There have been a
few studies on relay starts (Gambrel et al. 1991, McLean et al. 2000).
McLean et al. (2000) investigated the effectiveness of step starts in the
case of collegiate male swimmers who were given instruction on step
starts over a four-week period. These researchers reported that step starts
were effective relay starts. However, they did not consider the relay time
when evaluating the start performance.
The step start is considered a more difficult technique than a start
involving no steps (no-step start) because swimmers often place their
foot on the edge of the starting block by mistake. The swimmer cannot
generate satisfactory horizontal velocity on the block if the foot placement
is incorrect. It is necessary to determine the best relay start by
taking into consideration the time taken to change swimmers during the
relay and the difficulty each swimmer faces in the step start. The purpose
of the present study was to evaluate the effectiveness of the three types
of relay starts in order to determine the relay start performance while
considering the relay time and the difficulty faced during step starts.
Methods
Eight well-trained male college swimmers participated in this study.
Their mean height, mean body weight and mean age were 177.9 ± 5.7