Biomechanics and Medicine in Swimming XI

comprised of an instrumented start block constructed using a Kistler
force platform (Z20314, Winterthur, Switzerland, figure 2). Wetplate
not only allows for the determination of the overall force profile of
the start itself but also allows measurement of the grab force through
two Kistler tri-axial transducers (9601A) placed in a bar at the front
of the start block. The contribution of the rear foot is also measured on
a second instrumented incline plate by 4 Kistler tri-axial transducers
(9251A) developed to the specifications of the OSB11 start platform.
The system includes a series of calibrated high speed digital cameras
(Pulnix, TMC-6740GE), one above water to capture the start and
entry with 3 underwater to obtain vision from 0m to 15m. The timing
to 5m and 7.5m was assessed using ‘SwimTrak’ an analogue video
camera timing system in which the cameras (Samsung, SCC-C4301P)
were located perpendicular to the plane of motion at 0m, 5m and 7.5m.
Deinterlacing the video signal allowed for the respective split times to
be determined to a resolution of 1/50 th of a second. All calculations were
timed from when the participants head passed the specified points.
Figure 2: The AIS Wetplate Instrumented Starting Platform with Grab
bar and Kick Plate
Data was collected for a total of 12 seconds, 1 second prior to and 11
seconds after the start signal. The start signal is integrated into the analysis
system and triggers the data collection from the force plates and the
cameras. A 10Hz Butterworth low pass digital filter was applied to the
force data collected through Wetplate.
A two way repeated measures analysis of variance (ANOVA) was
performed to assess the main effects of style (Kick Start vs. Track Start)
and gender (male vs. female). When the assumption of equal variances
was violated, significance was adjusted using the Greenhouse-Geisser
procedure (Vincent, 1995). All presented values are expressed as mean
± SD, and P values less than or equal to 0.05 were considered as statistically
significant.
results
The performance differences between the kick start and traditional track
start are presented in Table 1. Males recorded faster times and higher
velocities than females for both the track start and the kick start. However
there were no significant interactions between gender and the style
of the start for any of the variables and so results were pooled in Table 1.
All force data presented has been normalised to the participant’s weight
and expressed in Body Weights (BW).
chaPter2.Biomechanics
Table 1: Comparison between Kick Start and Traditional Track Start.
Mean and SD
Variables Kick Start Track Start
Significance
Level
Time to 5m (s) 1.62 ± 0.01 1.66 ± 0.01 0.002**
Time to 7.5m (s) 2.69 ± 0.02 2.73 ± 0.02 0.032*
Time on Block (s) 0.77 ± 0.01 0.80 ± 0.01 0.001**
Take-off Horizontal Velocity (m/sˉ¹) 4.48± 0.04 4.41 ± 0.03 0.009**
Average Velocity between 5m & 7.5m
(m/sˉ¹)
2.39± 0.04 2.37± 0.04 0.644
Average Horizontal Force (BW) 0.60± 0.01 0.57 ± 0.01 0.003**
Peak Horizontal Force on the Block
(BW)
1.13± 0.04 1.09 ± 0.04 0.151
* Significant difference between Kick Start and Track Start p < 0.05
** Significant difference between Kick Start and Track Start p < 0.01
dIscussIon
This study hypothesized that the kick start would increase the amount of
horizontal force being applied when compared to the track start, enabling
shorter start times and greater horizontal velocity off the block. Results
showed the kick start was the significantly superior method when looking
at performance indicators of time to 5 m and time to 7.5 m.
This study included nine male subjects, but only five females. It is
possible the different subject numbers may have masked differences between
genders owing to a reduced statistical power. The main intent
of this study, however, was to investigate differences between the start
techniques, not to determine whether strategies would be different for
males and females.
The new block allows the kick start to achieve an average on block
time of 0.77s compared to the track starts of 0.80s. This was significant
(p