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2013). Placement of feet above the water surface is
also better in terms of speed start (p <0.01) in, and
take-off horizontal (p = 0.01) in comparison with the
placement of feet under the water, but have a smaller
horizontal peak power (p = 0:02) (Nguyen et al.,
2014).
The mechanical principle of movement at the
start of swimming is associated with the action-
reaction principle (Third Newton ‘Laws). If there is
any change of state from static to motion, or from
motion to static, there must be cause or influence.
The influence or cause is the style. At the bottom
start of the backstroke-swim style, there is a force
called propulsive force (Stager and Tanner, 2005).
The force works when the foot does repulsion
against the block starting wall, causing the body to
have back repulsion. When the force occurs, an
angle formed by the shin, knee joint, and thigh bone
is formed. If the resulting angle is smaller and the
body is more inclined forward, in other words the
horizontal distance from the point of the body
should be minimized, or the weight point near to the
side of the pedestal, it will produce an increased
movement speed to a direction. The principle of
action-reaction also explains that to produce a large
reaction, a strong support is needed. A strong
pedestal will produce good power (Grimshaw and
Burden, 2007; McGinnis, 2013).
Using the basis of movement mechanical
principle, the aim of this study is to compare the
repercussions between the parallel and staggered
feet placements, in which their repulsions consist of
the following components: initial angle, angular
velocity, and reaction time. Therefore, the
hypothesis of this research are as follows: (1) Is
there an initial angular difference between parallel
and staggered foot placements? (2) Is there a
difference in angular velocity between parallel and
staggered feet placements? (3) Is there any
difference in reaction time between parallel and
staggered feet placements?
2 METHODS
The samples in this study were eight athletes of
backstroke-swimming style from the Aquatic SAU
at UPI (Average age: 18.9 years old, weight: 62kg,
height: 174cm). Samples were set based on
the characteristics of the swimmer's ability by using
purposive sampling.
The used research method used was experimental
method with one-shot case study design (Fraenkel,
Wallen and Hyun, 2012). The experiment was
conducted three times for each feet position
(staggered and parallel). Both of the feet position
were placed on the surface of the water (Emerson)
with consideration to avoid water resistance and
slippage. All three experiments were recorded using
a digital video camera placed at a distance of 5
meters (Vantorre et al., 2010; Vantorre, Chollet and
Seifer t, 2014; de Jesus et al., 2015) and operated at
a frequency of 60Hz (underwater camera nikon
coolpix aw110) . Next, the video image is processed
by kinovea software to see the swimmer’s
movements during the start of repulsion. Measurable
components using this software are distance, angle,
coordinate point, and speed (Kinovea, 2015).
Figure 1: Parallel (a) and staggered (b) feet placements.
3 RESULTS AND DISCUSSION
Table 1 shows descriptive data from the results of
parallel and staggered foot placement repulsions for
three trials. The average angle formed early in the
first experiment is smaller than experiments 2 and 3
both for positioning of parallel (44.87 º ± 5.92) or
staggered (45.88 º ± 9.57) feet, so is with angular
velocity which shows better numbers in the first
experiment (parallel = 286.36º / s ± 26.83; staggered
= 281.43º / s ± 64.60). This can happen because in
the first experiment the sample had not experienced
fatigue. There is a causal relationship between
muscle fatigue and high intensity exercise. High
intensity exercise with anaerobic metabolism can
lead to decreased contractile function (Westerblad,
Allen and Lännergren, 2002). In this case the athlete
was in maximum capacity to produce power or
power output (Vøllestad, 1997). The average angle
of initial angle and angular velocity (table 1a) of the
two feet’s in each experiment indicates that there is
conformity with the presumption of the mechanical
movement described previously, that if the formed
initial angle is small, it will result in a velocity
Is Staggered Greater Than Parallel Feet Placement? - Kinematic Analysis for the Start of Backstroke-Swim Style
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