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Sports Biomechanics
ISSN: 1476-3141 (Print) 1752-6116 (Online) Journal homepage: https://www.tandfonline.com/loi/rspb20
How do elite artistic swimmers generate fluid
forces by hand during sculling motions?
Miwako Homma, Yuma Okamoto & Hideki Takagi
To cite this article: Miwako Homma, Yuma Okamoto & Hideki Takagi (2019): How do elite artistic
swimmers generate fluid forces by hand during sculling motions?, Sports Biomechanics, DOI:
10.1080/14763141.2019.1671485
To link to this article: https://doi.org/10.1080/14763141.2019.1671485
© 2019 The Author(s). Published by Informa
UK Limited, trading as Taylor & Francis
Group.
Published online: 13 Nov 2019.
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How do elite artistic swimmers generate fluid forces by hand
during sculling motions?
Miwako Homma , Yuma Okamoto and Hideki Takagi
Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan
ABSTRACT
The purpose of this study was to clarify how elite artistic (synchro-
nised) swimmers generate fluid forces with their hands during two
kinds of sculling motions: flat sculling in the back-layout position
and support sculling in the vertical position. We used the pressure-
distribution measuring method to estimate unsteady fluid forces
acting on the hand during sculling motions performed by seven
elite artistic swimmers. In addition, we simultaneously analysed
sculling motions using three dimensional-direct linear transforma-
tion methods. We found that sculling motions continuously gen-
erated fluid forces that are large during the stroke phase and small
during the transition phase. Lift force was efficiently generated,
and a large upward propulsive force was obtained during the
stroke phase in both flat and support sculling. During the outside
transition from out- to in-sculling, the net vertical load (= gravita-
tional force—buoyant force) was supported by the drag force. In
both flat and support sculling, artistic swimmers generated an
even fluid force in the upward direction during the in-sculling
and out-sculling phases to maintain a stable position.
ARTICLE HISTORY
Received 4 November 2018
Accepted 16 September 2019
KEYWORDS
Flat sculling; support
sculling; pressure
distribution; unsteady fluid
force; motion analysis
Introduction
In artistic swimming, which is also known as ‘synchronised swimming’,flat sculling is used
to maintain a horizontal position and support sculling is used to maintain vertical positions.
Homma (2017) reported net vertical load (= gravitational force—buoyant force) values for
eight female artistic swimmers with an average weight of 52.7 ± 4.40 kg: 7.77 ± 0.95 kgf at
the highest ballet-leg position, in which one leg is raised above water in the back-layout
position and 12.95 ± 1.72 kgf at the highest ballet-leg double position, in which both legs are
raised above the water. Based on these results, it is clear that sculling is needed to maintain
body position and provide an upward propulsive force to balance the net vertical load.
Sculling is an important technique used not only for supporting and maintaining balance
for body positions (Nesbitt, 1991), but also for propulsion, changing direction, and rotation
(Forbes, 1989; Homma & Homma, 2006; Lundholm & Ruggieri, 1976). Thus, it is an
indispensable technique for artistic swimming.
Several kinematic studies have investigated various sculling techniques, most of which
have focused on motion analysis (Francis & Smith, 1982,1983; Gomes et al., 2014;Hall,
CONTACT Hideki Takagi takagi.hideki.ga@u.tsukuba.ac.jp
SPORTS BIOMECHANICS
https://doi.org/10.1080/14763141.2019.1671485
© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License
(http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any
medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.
1985,1996; Homma & Homma, 2005,2006;Homma,Homma,&Washizu,2008;
Rutkowska-Kucharska & Wuchowicz, 2016; Rybuyakova, Lesgaft, & Pybyakova, 1991;
Zinzen, Antonis, Cabri, Serneels, & Clarys, 1992). In particular, for flat sculling, Homma
and Homma (2005) analysed flat sculling techniques used by ten elite artistic swimmers
employing a three dimensional-direct linear transformation (3D-DLT) method. Sculling
techniques for more advanced artistic swimmers included holding the elbows and upper
arms stationary and changing the attack angles of the hands smoothly and evenly. Motion
characteristics of flat sculling include spreading elbows to the outside, combining forearms
and hands into a single unit, and using horizontal motions during sculling. The trajectory
of the hands during sculling do not transverse a figure eight, as described in most training
conventions. Instead the hand trace a droplet-shaped figure with the inside tapered.
Homma and Homma (2006) analysed support sculling movements performed by 10
world-ranked artistic swimmers using the 3D-DLT method. During support sculling,
swimmers kept their elbows and upper arms stationary and their forearms horizontal.
Palms faced downwards throughout the sculling motion and the attack angle of the
hands was maintained to produce an effective vertically upward force.
Characteristics of elite artistic swimmers’motions during flat and support sculling are
reported in previous kinematic studies. Sculling motions produce propulsive forces by
imparting momentum to water or any other medium, thus generating various fluid forces.
Analysis of sculling therefore requires measurement of fluid force generated by the hands.
A few studies are available on fluid forces generated during sculling motions (Diogo et al.,
2010; Gomes et al., 2019; Gomes, Tremea, Silveira, de Souza Castro, & Loss, 2011; Homma,
Kawai, & Takagi, 2016; Kamata, Miwa, Matsuuchi, Shintani, & Nomura, 2006;Lauer,
Rouard, & Vilas-Boas, 2016; Takagi et al., 2014). Gomes et al. (2011) analysed the effective
propulsive force produced one swimmer when sculling in a vertical position with head
above the water’s surface. Each cycle was divided into four phases: in-sweep, transition
from in-sweep to out-sweep, out-sweep and transition from out-sweep to in-sweep. Force
was almost constant across all phases (approximately 9.5 N). Takagi et al. (2014) investi-
gated how unsteady forces are generated during sculling by a competitive swimmer using
particle image velocimetry (PIV) to acquire data on the kinematics. They found that
a skilled swimmer produces large unsteady fluid forces when a leading-edge vortex forms
on the dorsal side of the hand and wake capture occurs on the palm side. Homma et al.
(2016) analysed hydrodynamic forces acting on the hand during flat sculling and support
sculling by one elite artistic swimmer. Their results were consistent with the findings of
Takagi et al. (2014). However, in the above reports, a single participant was studied or the
participant was not an artistic swimmer. How elite artistic swimmers generate fluid forces
by hand during sculling remains unclear.
To estimate the fluid forces, a pressure-distribution method recently became available
for underwater measurements. This method directly measures pressure distributions on
hands of swimmers using small pressure sensors. The method enables estimation of forces
generated in a fluid under variable conditions, such as those produced during sculling.
Momentum vectors and acceleration constantly change during sculling (Kudo, Yanai,
Wilson, Takagi, & Vennell, 2008; Takagi & Sanders, 2002; Takagi & Wilson, 1999). Since
the experimental procedure involves only equipping the hand with a sensor for making
periodic measurements, the method can be easily used during training. The effectiveness of
the method for evaluating propulsion techniques has been demonstrated in previous
2M. HOMMA ET AL.
studies (Takagi et al., 2014; Tsunokawa, Takagi, Sengoku, & Tsubakimoto, 2012). The
above information suggests that valuable information on effective sculling motions can be
obtained by estimating fluid forces generated on swimmers’hands during sculling usingthe
pressure-distribution measuring method. Characteristics of propulsive force generated by
elite artistic swimmers, including magnitude and direction, has not been investigated.
The objective of this study was to estimate unsteady fluid forces on the hands during
sculling motions (flat and support) using pressure-distribution measurements and to
clarify characteristics of propulsive force generated by elite artistic swimmers, including
magnitude and direction, has not been investigated. We hypothesise that elite artistic
swimmers generate vertical upward fluid forces continually to support their net vertical
load in both sculling motions. Data that emerges from this study are expected to
become useful for all athletes and coaches involved the artistic swimming to enhance
swimmer performance.
Methods
Participants
Participants in this study were seven elite female artistic swimmers. Participants were all
proficient swimmers who were members of the Japanese National Team; five partici-
pated in the London Olympics in 2012 or the Rio de Janeiro Olympics in 2016 or both,
and the other two competed in the World Swimming Championships in 2013 (Table 1).
This study was conducted with approval from the Research Ethics Committee of the
Faculty of Sports, University of Tsukuba and Health Sciences and following the
Helsinki Declaration. Participation in the experiment was agreed to by each swimmer
after the purpose and the method of this study were fully explained.
Experiment
Flat sculling in the stationary back-layout position and support sculling in the station-
ary vertical position (Figure 1) were each performed for 5 s. Participants were
instructed to maintain the same body height as much as possible during both sculling
motions.
Sculling motions were monitored using four video cameras (Figure 2), which were
set with a shutter speed of 1/500 s and a sampling frequency of 60 Hz. A calibration tool
Table 1. Characteristics of participants.
Age Height Weight
Swimmers (yr) (cm) (kg) Best results at the Olympics and World Champs
A 25 167.9 54.3 4th at 2013 World Champs
B 24 159.4 48.3 5th at 2012 Olympics, 4th at 2017 Worlds
C 22 169.2 52.8 4th at 2013 World Champs
D 22 165.1 53.6 5th at 2012 Olympics
E 22 176.1 65.0 3rd at 2016 Olympics
F 19 168.5 57.1 3rd at 2016 Olympics
G 21 166.5 54.7 5th at 2012 Olympics, 4th at 2013 Worlds
Mean 22.1 167.5 55.1
SD 2.0 5.0 5.1
SPORTS BIOMECHANICS 3
(1.6 m × 1.82 m × 1.3 m) and 168 control points were used to reconstruct 3D
coordinate space by the DLT algorithm. A fixed coordinate system (x-y-z) corresponded
to the calibration tool. In the longitudinal direction while participants were performing
the trials, left and right were considered the x-axis, front and rear the y-axis, and up and
down the z-axis. The errors that occurred during recreation of calibrated coordinates
were 0.0028 m (x-axis), 0.0038 m (y-axis) and 0.0047 m (z-axis). Light-emitting diode
(LED) markers were placed at three points on the participants: 1) lateral aspect of the
Figure 1. Flat sculling in the back-layout position (left) and support sculling in the vertical position
(right).
4 m
AD Converter
( PCD-330B-F ) LED
PC ( PSC100-A )
Camera 1Camera 2
Camera 3
Camera 4
Pressure sensors
on a left hand
25 m
y
0
x
12 m
10 m
Figure 2. Experimental apparatus and a layout of cameras.
4M. HOMMA ET AL.
left wrist, 2) medial aspect of the left elbow and 3) the left acromion. Marking points on
the left hand were the tips of the first, third and fifth fingers. Four video cameras were
synchronised using an LED lamp (PH-110, DKH, Japan) in the view-angle of each
video camera. To synchronise the video cameras with pressure data, the LED lamp in
the view of the video cameras and the electric signal to flash the LED lamp were used as
triggers. A switch that generated an electric signal was used to flash the LED lamp. The
same electric signal was fed to the sensor interface, which initiated recording via the
pressure sensor.
Small waterproof pressure sensors (PS.05KC, Kyowa, Japan) were attached to six
points on each participant’s left hand to measure pressure distributions during sculling
motions. Before the experiments, all pressure sensors were carefully calibrated based on
a relationship between water depth and hydrostatic pressure (mean error: 2.3%). Using
previous studies (Ozaki, Matsuuchi, Takagi, & Nakashima, 2008; Ozaki, Takagi,
Nakashima, & Matsuuchi, 2009), pressure sensors were attached to three areas of the
hand: thumb, and middle and little fingers, as shown in Figure 3, on both the palm and
the dorsum. On the dorsum, sensors were attached around the metacarpophalangeal
joints of the second, third and fourth fingers, and the sensors on the palm corresponded
with those on the dorsum (Figure 3). The hand was sectioned into the following three
longitudinal areas: thumb, from the first finger to the border of the second and third
fingers; middle, from the border of the second and third fingers to the border of the
third and fourth fingers; and little, from the border of the third and fourth finger to the
fifth finger. A pressure sensor was attached to each area on the palm and the dorsum of
Thumb Little
Middle P4P5P6 P1P2P3
Figure 3. The hand area which is divided into three and the attachment position of the six pressure
sensors on the palm side and the dorsal side.
SPORTS BIOMECHANICS 5
the hand using acrylic air-tight waterproof tape and vinyl tape. Signals from pressure
sensors were collected by data acquisition software (DCS-100A, Kyowa, Japan) via
a sensor interface (PCD-330B-F, Kyowa, Japan), and were recorded on a personal
computer with a sampling frequency of 200 Hz.
Definition of sculling phase
As previously defined (Homma & Homma, 2005,2006), the outermost position (from
the body) was defined as Out and the innermost position as In. The phase from In to
Out was defined as the out-sculling phase and the phase from Out to In as the in-
sculling phase. Sculling comprised two phases. The elbow angle in the x-y plane was
used for flat sculling and the pronation/supination angle of the forearm in the x-y plane
for support sculling to distinguish these phases. The elbow angle was defined as an
angle between a line joining the acromion, medial aspect of the elbow and medial aspect
of the wrist. The definition of each phase was as follows:
Out-sculling phase: The phase from the minimum value (In) of the elbow angle and
the pronation/supination angle of the forearm to the maximum value of these two
angles.
In-sculling phase: The phase from the maximum value (Out) of the elbow joint angle
and the pronation/supination angle of the forearm to the minimum value of the two
angles.
Data analysis
A sculling cycle starts at the In position with the hand placed the closest to the centre of
the body. One cycle, which was the most stable motion from three cycles in the middle
part of each trial, was analysed. Numerical analysis software (MATLAB, MathWorks,
USA) was used to interpolate the pressure data to 60 Hz using spline interpolation.
Pressure values and actual coordinate values were smoothed using a low-pass
Butterworth digital filter with a cut-offfrequency at 6 Hz (Tsunokawa et al., 2012).
Each marking point on the body recorded in the images was manually digitised using
the motion-analysis software (Frame DIAS IV, DKH, Japan), and actual coordinates on
the fixed-axis system were calculated using the 3D-DLT method.
We assumed that the thickness of the palm and the dorsum of the hand was small. In
addition, the dynamic pressure on the hand due to sculling was estimated by first subtract-
ing the pressure on the dorsum of the hand from that on the palm and then eliminating the
effect of static pressure at the location of the pressure sensor. The measured pressure value
for each area was taken as a representative value. The fluid force on each area was calculated
by multiplying the calculated dynamic pressure by the projected area. The projected area of
the three areas constituting the hand was calculated by a quadrature method through visual
observation, with the hand forms described on grid paper with 1 mm intervals. The sum of
fluid forces in the three areas was defined as the fluid force on the entire hand (F
hand
). The
reliability of F
hand
measured by pressure distribution has been reported in previous studies
(Takagi & Wilson, 1999).
6M. HOMMA ET AL.
Definitions and calculations of kinematic parameters and directions of fluid
forces
Marking points on the hand were labelled as points M
1
(third fingertip), M
2
(first
fingertip) and M
3
(fifth fingertip) and are shown in Figure 4(a). We assumed that the
midpoint between M
2
and M
3
was the centre of the hand. The midpoint between M
2
and M
3
was defined as point C, and the velocity of the hand (V
H
) was obtained by
taking the derivative of the displacement at point C.
The fluid-force vector and the hand-attachment angle were calculated from actual
coordinate values obtained via motion analysis; thus, a moving axis system H(X-Y-Z)
originating from point C was defined (Figure 4(a)). When defining this system, the
Y-axis was set along the line connecting point C and point M
1
, and the Z-axis was set to
be perpendicular to the line joining C to M
1
, and C to M
2
. The X-axis was set
perpendicular to both Zand Y. Here, V
H
is defined as the velocity vector and was
transformed into the moved axis system H.
The attack angle θwas defined as the angle of V
H
with respect to the X-Y plane. In
addition, since the estimated fluid force acted perpendicularly on the hand, it was
assumed that the direction of vector Zand the fluid force crossed at point
C. Consequently, the direction of the fluid force was determined based on vector Z,
and the fluid-force vector acting on the hand was calculated (F
hand
). However, since not
all fluid forces on the hand acted as propulsive forces during sculling, it was necessary
to consider the direction in which the fluid force was applied. Thus, a unit vector was
obtained from vector Z, and the fluid-force vector on the hand was divided into the
three directions (x, y and z). Force in the direction of the swimmer’s propulsion [or the
perpendicular direction (z-axis)] was denoted by F
z
and defined as the upward propul-
sive force. Moreover, the forces on the x- and y-axes were denoted as F
x
and F
y
,
respectively (Figure 4(b)). The force which acts in a direction perpendicular to V
H
was defined as lift and the force which acts in a direction opposite to the V
H
was
defined as drag.
ab
M1
M3
M2
C
X
Z
Y
Fhand
Fx
Fz
X
C
Angle of attack θ
V
H
Lift
Drag
Figure 4. Definitions of the local coordinate system on a hand (a) and a definition of the angle of
attack, various components of the fore (b).
SPORTS BIOMECHANICS 7
Analysis items
The analysis items were:
(1) F
hand
: sum of fluid forces acting on the entire hand (N). F
hand
is measured
without considering direction, and it assumes a positive value when the palm
generates fluid force on the water.
(2) F
x, y, z
:fluid force in each direction (N). F
z
is the fluid force generated by the
palm in the direction of propulsion; it assumes a negative value when the
swimmer pushes water vertically downward and generates upward fluid force.
(3) P
1- 6
: pressure measured by each sensor (N/m
2
).
(4) Sculling velocity: composite velocity of the hand (m/s).
(5) Sculling time: time required for sculling (s).
(6) Angle of attack: the angle of the hand with respect to the velocity vector (deg).
(7) Sculling pattern: orbit of the hand on the x-z plane.
Mean values of the kinematic and kinetic variables were calculated. Data comparison
between Out-sculling and In-sculling in each sculling technique within the participants
was conducted by using paired t-tests, and the significance level was set at p< 0.05.
Results
Motion analysis of the upper limb
Sculling time, velocity and angle of attack in flat and support sculling are shown in
Table 2. The sculling time during the out-sculling phase was significantly longer than
that during the in-sculling phase in both sculling techniques. Moreover, the velocity
during the in-sculling phase was significantly higher than during the out-sculling phase.
As a typical example, a) the temporal change in the sculling velocity, b) the angle of
attack during one cycle and c) the sculling pattern of the cycle during the two kinds of
sculling (flat sculling in swimmer G and support sculling in swimmer C) are shown in
Figures 5 and 6, respectively.
For all swimmers in both sculling modes, sculling-velocity peaked during strokes
showing a curve with bimodal characteristics (See Figures 5(a) and 6(a)). The angle of
attack increased from the start of the sculling until the stroke of the out-sculling phase.
The mean angle of attack during the stroke was 33.8 ± 2.07° for flat sculling and
27.2 ± 4.11° for support sculling. Later, the angle gradually increased during the
outward transition which is a switching phase from out- to in-sculling phase, assuming
Table 2. Sculling time, velocity and attack angle for flat sculling and support sculling.
Flat Sculling (N = 7) Support Sculling (N = 7)
1 cycle Out Scull In Scull 1 cycle Out Scull In Scull
mean SD mean SD mean SD mean SD mean SD mean SD
Scull time (s) 0.59 0.07 0.33 0.03** 0.26 0.05 0.67 0.02 0.38 0.02*** 0.30 0.02
Scull velocity (m/s) 1.34 0.17 1.25 0.14 1.45 0.22** 2.21 0.12 1.99 0.12 2.47 0.15***
Angle of attack (deg) 33.81 2.07 29.81 3.21* 37.28 3.67 27.19 4.11 31.18 7.00 23.78 8.11
Note: *p< 0.05, **p< 0.01, ***p< 0.001, a significant difference between Out Scull and In Scull.
8M. HOMMA ET AL.
a maximum value of 60–70° for both sculling modes. The angle then gradually
decreased during the inward transition which is a switching phase from in- to out-
sculling phase, and assumed a minimum value of 1–17º for flat sculling and 0–14º for
support sculling (See Figures 5(b) and 6(b)).
Flat sculling showed a drop-shaped pattern with a sharp corner inside. Patterns
exhibited higher In (closer to the surface) and lower Out. The hand moved almost
horizontally during the stroke for the out-sculling phase; it moved towards the bottom
of the pool during the outward transition (See Figure 5(c)). For support sculling, all
swimmers except one exhibited elliptical patterns with a shaper corner inside, and their
1: First peak of F
hand
2: Smaller value of F
hand
on the outside transition
3: Changing point from out-sculling to in-sculling
4: Sec ond peak of F
hand
x (m)
z (m)
1
2
3
4
-0.4
-0.3
-0.2
-0.1
0
00.10.20.30.40.5
0.6
c
0
0.5
1
1.5
2
0 0.1 0.2 0. 3 0.4 0.5
Out-sculling In-sculling
0
20
40
60
0 0.1 0.2 0.3 0.4 0.5
)s/m(yticoleV(kcattAfoelgnAged)
v
Time (sec)
a
b
0
10
20
30
40
0 0.1 0.2 0.3 0.4 0.5
F hand
Out-sculling In-sculling
d
Force (N)
Force (N)
e
-30
-20
-10
0
10
20
30
0 0.1 0.2 0.3 0.4 0.5
x
y
z
Time (sec)
Figure 5. Changes in hand moving velocity (a), angle of attack (b), movement locus of the origin of
a hand (c), resultant force: F
hand
(d) and three-direction component of force: F
x, y, z
(e) during flat
sculling for swimmer G.
SPORTS BIOMECHANICS 9
hands moved almost horizontally after they switched the direction of the hands in front
of their body and during the out-sculling phase (See Figure 6(c)).
Fluid force acting on the hand
Table 3 shows maximum, minimum and mean fluid force, mean impulse on the entire
hand (F
hand
), and fluid force in the propulsion direction (F
z
) during flat and support
1: First peak of F
hand
2 : Smaller value of F
hand
on the o utside transition
3 : Changing point from out-sculling to in-sculling
4 : Seco nd peak of F
hand
-0.4
-0.3
-0.2
-0.1
0
00.10.20.30.40.5
0.6
1
2
3
4
x (m)
z (m)
c
0
20
40
60
80
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
F hand
0
0.5
1
1.5
2
2.5
3
3.5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Out-sculling In-sculling
0
20
40
60
80
0 0.10.20.30.40.50.60.7
v
)s/m(yticoleV
(kcattAfoelgnAged)
Time (sec)
a
b
Out-scull In-sculling
d
e
Force (N)
Force (N)
-60
-40
-20
0
20
40
60
80
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
x
y
z
Time (sec)
Figure 6. Changes in hand moving velocity (a), angle of attack (b), movement locus of the origin of
a hand (c), resultant force: F
hand
(d) and three-direction component of force: F
x, y, z
(e) during support
sculling for swimmer C.
10 M. HOMMA ET AL.
sculling. As a typical example, d) the temporal change in the resultant fluid force (F
hand
)
and e) three-direction component of force (F
x, y, z
)inflat and support sculling are
shown in Figures 5 and 6, respectively.
F
hand
in both sculling modes peaked during the out-sculling phase and in-sculling
phase (See Figures 5(d) and 6(d)), and F
hand
was less during transitions which is
a switching phase either from in- to out-sculling or from out- to in-sculling phases.
A curve with bimodal characteristics was seen for all swimmers. For flat sculling, no
significant difference was observed in maximum and mean F
hand
between the in-
sculling and out-sculling phases; however, a significant difference for minimum F
hand
and impulse F
hand
was found between in-sculling and out-sculling phases. As with
F
hand
, a significant difference for minimum F
z
and impulse F
z
was found between in-
sculling and out-sculling phases, but no significant differences were found for max-
imum and mean F
z
. For support sculling, maximum F
hand
during the in-sculling phase
was significantly higher than that during the out-sculling phase by approximately 25 N.
Discussion and implications
In competitive swimming, a swimming stroke has phases that generate propulsive force
and phases that do not (Maglischo, 2003). Nevertheless, this study shows that sculling
motions continuously provide vertically upward fluid force (F
z
), and all phases are
propulsive. This result is consistent reports from Francis and Smith (1982,1983) and
Homma et al. (2016).
The fluid force waveform (F
hand
) in both sculling motions showed a curve with
bimodal characteristics. This finding implies that the stroke phase produces the larger
propulsive force and the transition phase generates less propulsive force. This result is
consistent with reports from Takagi et al. (2014) and Gomes, Boeira, and Fagundes
(2017). During a stroke in which fluid force peaks, the sculling velocity peaks almost
simultaneously, and the angle of attack at that moment is 20–50°. Schleihauf (1979)
studied lift generation by propulsive force under steady conditions via a wind-tunnel
experiment using a hand model and showed that an angle of attack of approximately
40º maximises the lift component. Zielinski (2005) reported that elite synchronised
Table 3. The maximum, minimum, mean, and impulse of F
hand
and F
z
for flat sculling and support
sculling.
Flat Sculling (N = 7) Support Sculling (N = 7)
1 cycle Out-sculling In-sculling 1 cycle Out-sculling In-sculling
Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD
F
hand
Maximum (N) 33.36 9.14 30.43 8.34 31.02 9.76 72.08 17.64 46.17 8.90 71.44 18.51*
Minimum (N) 10.42 3.42 12.63 3.44* 10.63 3.50 9.88 5.90 11.42 5.56 15.34 8.83
Mean (N) 22.65 5.87 22.97 5.87 22.32 6.53 42.30 8.00 34.78 5.80 46.43 19.00
Impulse (Ns) 13.47 3.14 7.42 1.73* 6.05 1.63 29.19 5.86 13.14 2.44 16.05 5.09
F
z
Maximum (N) −27.47 7.25 −25.65 6.96 −22.55 6.92 −54.46 8.26 −43.23 9.48 −53.70 8.74
Minimum (N) −7.90 2.50 −11.95 3.34** −7.95 2.51 −8.08 4.93 −10.66 5.71 −12.56 6.96
Mean (N) −17.50 4.57 −19.00 5.55 −15.73 4.67 −32.76 5.67 −31.02 6.37 −34.72 11.15
Impulse (Ns) −10.42 2.41 −6.16 1.67* −4.26 1.15 −22.62 4.23 −11.72 2.54 −10.90 3.78
Note: * p< 0.05, **p< 0.01, a significant difference between Out Scull and In Scull.
SPORTS BIOMECHANICS 11
swimmers displayed angles of attack of 20–50º. The above findings suggest that
swimmers in this study effectively generated the lift during a stroke. Swimmers showed
an angle of attack of 60–70° during the outward transition and sculled downward, and
they likely supported the net vertical load by using drag forces during the transition
from out- to in-sculling. These results are again consistent with previous studies
(Francis & Smith, 1982,1983; Homma & Homma, 2005,2006; Homma et al., 2008).
These studies indicated that the horizontal stroke significantly contributes to lift and
generates a propulsive force with a large drag component in during outward transition.
The trajectory of the hands during sculling was clarified and did not transverse a figure
eight, as described in several manuals for coaches and swimmers (DeNegri &
McGowan, 2005; Lundholm & Ruggieri, 1976; Rybuyakova et al., 1991; Yates &
Anderson, 1958; Zielinski, 2001,2005). Rather, hands traced a droplet-shaped figure
with the inside tapered.
As expected, the fluid force and the impulse of the out-sculling phase and the in-
sculling phase were similar in flat sculling. We did not expect the same result for
support sculling. Support sculling is a technique unique to artistic swimming because it
involves external and internal rotations of the shoulders in addition to supination and
pronation of the forearms. Homma and Homma (2006) and Homma et al. (2008)
reported that when artistic swimmers executed support sculling techniques their
shoulders are rotated external and forearms are kept in supination to maintain
a constant angle of attack during the out-sculling phase. When in-sculling, the
shoulders are rotated internal and the forearms are kept in pronation to maintain an
optimal angle of attack, and the arms are then bought back to the front of the body.
Moreover, they scull in the shape of a quarter in the range from the centre of the front
of the body, where the arms can be easily moved, to the side of the body. In general, the
range of motion of the radioulnar joints in the supination of the forearms with the palm
facing inside at 0°, is approximately 80–90° (Thompson & Floyd, 2002). For this reason,
support sculling, which is performed the palms facing towards the head, is an unusual
because it is accomplished at almost the maximum range of motion of supination of the
forearms. This finding shows that the out-sculling phase, in which the arms move from
the front of the body to the side, is an anatomically difficult motion that does not
effectively activate muscles, but posture is easier to maintain because the arms are
opened to the left and right, coming to the side of the body. These findings suggest that
even though the out-sculling phase cannot attain a high velocity because of the difficulty
of the motion, it stabilises the position and lengthens sculling time, thereby producing
equivalent fluid force and impulse to those produced during the in-sculling phase. This
result corroborates the statement in the Star Program Manual by Synchro Canada
(2002), the most representative instruction manual in artistic swimming that indicates
that the forces in the out-sculling and in-sculling phases are the same.
Furthermore, in both flat and support sculling, the smaller fluctuation of F
z
value
over one cycle can contribute to the stability of the body. As clarified in this study,
even top athletes in the world cannot maintain to produce the steady F
z
over one
cycle. Therefore, it is important to minimise the fluctuation of F
z
as much as
possible. Arellano, de la Fuente, and Domínguez (2009) analysed sculling propulsive
arm actions in a horizontal position and concluded that the sculling propulsive
action helped body displacement in the inward-, transition(supination)-, outward-
12 M. HOMMA ET AL.
phase, while the other transition (pronation) phase had a reduced contribution. Our
findings that F
z
decreases during transitions is consistent with Arellano’sresults.We,
therefore, suggest that it is important to keep the propulsive force continuously by
shifting smoothly at the transition phases, i.e. a pronation and supination action of
the forearm.
There were some limitations that must be considered while interpreting study
results. The sample size was not sufficient for statistical analysis because participants
were limited to top ranked swimmers. Only left hand data were analysed regardless of
the participants’dominant hand. In the further study we should investigate fluid forces
generated by both right and left hand and increase the number of participants.
Conclusion
In this study, we used a pressure-distribution measuring method to estimate unsteady
fluid forces acting on the hand during sculling motions performed by elite artistic
swimmers. We found that sculling motions continually generate vertical upward fluid
forces, which are larger during a stroke and smaller during transitions, as we hypothe-
sised. Moreover, sculling motions produced equivalent vertical impulse forces during
the out-sculling and in-sculling phases; these forces help swimmers maintain a stable
position. In both flat and support scullings, it is recommended to move their hands
horizontally during out-sculling and to feel the water pressures by the hands continu-
ously throughout sculling. Additionally, for generating well-balanced impulse force
during the out-sculling and in-sculling phases for support sculling with a large vertical
net load, swimmers need advanced sculling techniques that involve forearm extra-
supination and external rotation of the shoulder.
Acknowledgments
This work was supported in part by the Faculty of Health and Sport Sciences, University of
Tsukuba. We are pleased to acknowledge the considerable to Dr. Takaaki Tsunokawa.
Disclosure statement
No potential conflict of interest was reported by the authors.
ORCID
Miwako Homma http://orcid.org/0000-0002-0531-4696
Hideki Takagi http://orcid.org/0000-0001-8797-7014
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