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(�) Biomechanical study on the success factors of the snatch in top female weightlifters in Japan
9
(1)
Biomechanical Study on Success Factors of
Snatch in Top Female Weightlifters in Japan
H. Nagao1 , Y. Kubo1 , T. Huang2 , Y. Morishita1
1National
Sports Science Center,2 Sports Okinawa
Abstract The purpose of this study was to determine the success factors of the snatch in topclass female weightlifters in Japan using biomechanical methods. The results of the analysis
showed that the barbell was not raised. The results showed no significant difference in barbell height
between the success and failure attempts. On the other hand, the amount of forward displacement,
backward displacement, and maximum forward velocity of the barbell were significantly smaller in
the success trials than in the failure trials. Success also resulted in significantly less forward
displacement of the body's center of gravity after the barbell reached its maximum height than
failure. These results suggest that in the case of a potentially raised snatch, the height of the raised
barbell is not a factor in the success of the snatch, but the amount of backward and forward
displacement of the barbell and the way the body moves under the raised barbell are factors in
success.
Keywords: weight lifter, motion analysis, barbell trajectory
to at least keep the record. The fewer the number of
1.
background
failed attempts, the more opportunities there are to
attempt higher weights in subsequent attempts, and the
The weightlifting competition consists of three
greater the likelihood of a good record. Therefore, a good
snatches and three clean and jerks, and the total of
performance in weightlifting requires a maximum lifting
the maximum lifting weights of each is used to
weight
determine the ranking. The weight of each attempt is
determined by the athlete's self-assessment according
to the record and rank he or she is aiming for, but
according to the rules, no attempt may be made with a
weight lighter than the weight of the previous attempt.
For this reason, many competitors use the strategy of
starting with a relatively light weight for the first
attempt and gradually increasing the weight in order
We believe that improving the success rate is
important as well as improving the
In general, the snatch has a lower lifting weight
than the clean and jerk. It is also said that the
snatch requires higher
technique1)
. The technique of
the snatch has been described in many studies
as consisting of six events and five phases of
the movement
(1st pull, transition, 2nd pull, turnover and catch
phases) (Figure
The first pull phase is similar to deadlift training, in
which the barbell is raised to knee height at a
relatively low
movements4)
speed
mainly by lower limb
.) The transition phase is characterized by
a recoil motion by flexion and extension
of the knee joint, known as double knee
bend5)
.
At this time, the barbell is displaced to the lifter's
rear side and approaches the lifter's body.
10 Biomechanisms 25
start
position
1st knee
max. ext.
1st pull
1st knee
max. flex.
transition
2nd knee
max. ext.
2nd pull
max. barbell
height
turnover
catch
position
catch
Figure 1 Definition of Snatch Phases and Events
The 2nd pull phase is the phase in which the
greatest force is
exerted2,3)
9)
Gourgoulis et al.
analyzed only successful and
. The sagittal trajectory of
unsuccessful attempts of the same weight of snatch
the barbell in the snatch is known to be S-shaped in
in six Greek national team lifters, in which the barbell
most
cases6,7)
. In the subsequent turnover phase, the
was dropped forward in the case of failure.
barbell is again displaced backward and reaches its
Comparison
maximum height. At this point, the lifter begins to
extremity joint motion revealed that the direction of
of
barbell
trajectory
and
move the barbell downward. During the catch phase,
the composite acceleration vector of the barbell in
the barbell is falling and the lifter must complete the
the 1st pull phase was closer to vertical in the
movement down to get into the catch position. One of
successful attempts than in the unsuccessful
the conditions for a successful snatch in competition is to
attempts, indicating the importance of pulling the
stand up and remain stationary with the barbell held
barbell straight up in the 1st pull phase. On the
above the head after the catch position. Therefore, if the
other hand, other variables related to barbell and
barbell is not brought to rest once in the catch position
lower extremity joint motion did not differ between
(vertical velocity of the barbell ≈ 0 m/s), it is not
the successful and unsuccessful trials. However,
possible to stand up and complete the snatch
the small sample size of this previous study points
successfully. In addition, a larger maximum raising height
out the low generalizability of the
results6)
lower
. The
9)
of the barbell would be advantageous because it
study by Gourgoulis et al. analyzed only the lower
would increase the time for the barbell to travel down
extremity joint movements up to the 2nd pull
and allow the barbell to come to rest. Based on the
phase,
above, the two main tasks to be accomplished for a
movements to catch the barbell during the turnover
successful snatch are to raise the barbell high enough
and catch phases. The comparison of the body
and to keep the barbell stationary in the catch position
center of gravity behavior in addition to the
(i.e., catch the barbell).
trajectory of the barbell and lower limb joint
8)
Stone et al. compared the barbell trajectories of
and
movements
did
not
during
examine
the
the
snatch
physical
between
successful and unsuccessful snatch attempts, but
successful and unsuccessful trials will provide
were unable to show statistically clear differences
new insights into the body movements required to
because they were comparing successful and
catch the barbell, especially after the turnover
unsuccessful attempts at different weights. In
phase.
addition, snatch failures can occur when the barbell
The purpose of this study was to determine the
is dropped forward or backward, and it is expected
success factors of the snatch in top-class female
that the trajectory of the barbell would differ
weightlifters
depending on the method of failure, but in this
methods. The hypotheses of this study were that the success
previous study, the trajectory of the barbell was not
factors of the snatch were 1) barbell height and 2) anterior-
different depending on the method of failure.
posterior displacement of the barbell and body. In
in
Japan
using
biomechanical
Biomechanical
Study on Success
Factorsofof the
Snatch in Top Female Weightlifters in Japan 11
order to(�)
compare
the success
and failure
snatch at the same weight for the same athlete, the
term "success" of the snatch in this study was defined as
12 Biomechanisms 25
The term "successful snatch" shall mean "a successful
snatch with a weight less than or equal to the
athlete's maximum lifting weight.
method
2.
2.1
subject of analysis
This study focused on the women's snatch at the
2016 All Japan Weightlifting Championships. There
were 64 female participants (including those who
abstained), and 172 snatch attempts, of which 119
(69.2%) were successful and 53 (30.8%) were
unsuccessful. Twenty-six
(49.1%) of the failed
attempts involved the barbell falling forward. Failure
to drop the barbell backward accounted for 24 (45.3%)
of the failed attempts, and 6 (11.3%) of the failed attempts
were due to other reasons such as press-out (an
illegal movement in which the elbow joint is not fully
extended when the barbell is held above the head) or
aborting the exercise in mid-performance. On the
other hand, 66 (66.7%) of the 99 failed snatch
attempts by male athletes involved a forward fall of
the barbell, and 27 (27.3%) involved a backward fall of
the barbell. In addition, the
Failures due to other reasons accounted for 6 trials
(6.1%). The top-class female athletes in Japan
were more likely than the male athletes to fail in
Given the large percentage of backward-falling
barbell failures and the fact that there have been no
previous reports analyzing the causes of backwardfalling barbell failures in Snatch failures, it would be
beneficial to gain knowledge on how to reduce the
number of backward-falling barbell failures. Therefore,
in this study, we decided to examine the success
factors of the snatch by comparing the failure to drop
the barbell backward to the success in the case of
failure. The 11 athletes who had both successful and
unsuccessful attempts at the same weight, and who
dropped the barbell backward in the case of failure,
were analyzed in terms of age, weight, and
Table 1 shows the weight of the athletes in the 48 kg,
53 kg, 58 kg, 63 kg, and 69 kg weight classes. The
weight classes analyzed were: 2 athletes in the 48 kg
class, 3 in the 53 kg class, 3 in the 58 kg class, 1 in
the 63 kg class, and 2 in the 69 kg class.
Study
on Success
Factors
of Snatch
Female
Weightlifters
in Japan
13
Table 1:(�)
Age,Biomechanical
weight, and lifting
weight
of snatches
of athletes
in in Top
axis
during
the 3-day
measurement
the analysis
period. The
obtained coordinate values were smoothed using a
Mean
S.D.
Max.
Min.
Butterworth type fourth-order low-pass digital filter
Age [yr.].
20.82
1.89
24
18
with a cutoff frequency of 6 Hz and no phase shift
Body mass [kg].
56.13
6.44
66.80
47.66
Snatch [kg].
71.82
8.82
85.0
61.0
based on previous
studies10,11) . The
left and right midpoints
of the limb and barbell position coordinates were
calculated, and the snatch movement was regarded
2.2
data collection
Two digital video cameras (SONY, HDR-CX700V)
were used to record the snatch movements. The
frame rate was 60 fps and the exposure time was
1/250 sec. The two cameras were positioned at
approximately 45°to the left and right of each
other,atadistance of approximately 20 m, with 0
directly in front of the platform on which the test was
performed. For calibration to the real-space coordinate
system, the cameras were positioned within 1.0 m
from the center of the platform (front-back), 1.5 m
(left-right), and 2.0 m (height).
The control points of 72 points were recorded at
the end of the competition. Permission was
obtained from the Japan Weightlifting Association to
record the video footage of the competition and to
use it for research purposes. The study was
approved by the Ethics Review Committee of the
National Center for Sports Sciences.
2.3
data processing
From the obtained video data, the 3D DLT
(direct linear transformation) method was used to
obtain the 3D real-space position coordinates of the
body end points, the anatomical osteophyte points
(parietal, right and left auricular, sternum superior
margin, right and left acromion, right and left elbow
joint, right and left wrist joint, right and left third
distal metacarpal, right and left greater trochanter,
right and left knee joint, left and right ankle joint, left
and right foot joint, right and left third distal
metatarsal, left and right foot tip), and the two end
points of the barbell. (distal ends of the left and right
metatarsals, left and right toes) and the threedimensional real-space position coordinates of both
end points of the barbell were obtained. The
standard error of calibration was 3 to 4 mm for each
as a two-dimensional movement in the sagittal plane.
14 Biomechanisms 25
Table 2 Definitions of kinematic and kinetic variables for
barbell
symbol
unit
definition
Vertical direction variable
Hip angle
Knee angle
Ankle angle
Figure 2 Joint angle
forward→
definition
Dy1
［m]
Start position to maximum height
Dy2
［m]
Start position to the catch position
Dy3
［m]
Maximum height to the catch position
pVy+_1st [m/s]
Maximum vertical linear velocity in
the 1st pull phase
pVy+_2nd [m/s]
Maximum vertical linear velocity in
the 2nd pull phase
pVy- [m/s]
Minimum vertical linear velocity in
the catch phase
DxL
Dx2
pFy_1st
［N]
Maximum vertical linear force in
the 1st pull phase
pFy_2nd
［N]
Maximum vertical linear force in
the 2nd pull phase
pPy_1st ［W]
Maximum vertical linear power in
the 1st pull phase
pPy_2nd ［W]
Maximum vertical linear power in
the 2nd pull phase
Dy3
D
Dx3
E
Dy2
Dy1
C
B
Dx1
A
Y
E：catch position D：
max. barbell height
C：2nd knee max. ext.
B：1st knee max. flex.
a
O
O: start position
n
Forward →
u
Figure 3nSchematic of barbell trajectory for snatch and variables
k
related to
n displacement
o
w
n
The results
of the analysis were analyzed as follows.
2.4 analysis
Height of peak vertical force position normalized by maximum
height
Horizontal direction variable
pFy% height ［%]
Dx1
［m]
Start position to most backward
position before the turnover phase
Dx2
［m]
Start position to the catch position
Dx3
［m]
Most backward position in the
2nd pull phase to the most
forward position
DxL
［m]
Most forward position in the 2nd
pull phase to the catch position
pVx+ [m/s]
Maximum horizontal linear velocity in the forward direction
pVx- [m/s]
Maximum horizontal linear velocity in the backward direction
Inertia coefficients were used. The angles of the hip
pFx+
［N]
joint, knee joint, ankle joint, trunk, and upper limb were
Maximum horizontal linear force
in the forward direction
pFx-
［N]
Maximum horizontal linear force
in the backward direction
In order to examine the body motion during the
snatch
, the
coordinates of thecenter of mass (COM) of the
athlete's body were obtained.
calculated (Figure 2). The trunk angle was defined as
the angle between the midpoints of the shoulders and
the midpoints of the greater trochanters and the
horizontal line, and was 0° when the body was bent
forward and level with the ground, and
The upper limb angle was 90°.The upper limb
angle was calculated by dividing the line segment of
the torso by the midpoints of the shoulders and then
dividing the upper limb by the midpoint of the
shoulders.
The angle between the wrist and the midpoint of both
Six events and five phases in the snatch based on
wrists was defined as the angle formed by the line
knee joint angle and barbell displacement
segments of the wrist and the midpoint of both wrists.
Defined based on previous
studies1-3)
(Figure 1). The
Biomechanical
Study as
on Success
Female
Weightlifters
in Japan as
15 the point at which the
starting(�)
position
was defined
a barbellFactors
heightofofSnatch
at in Top
The
catch position
was defined
least 0.225 m (barbell radius) and a barbell vertical
vertical velocity was closest to 0 m/s after the barbell
velocity of at least 0.1 m/s
reached its maximum height.
Based on the definitions shown in Figure 3 and
Table 2, the kinematic and kinetic variables of the
barbell were calculated for the successful and
unsuccessful trials. In addition, the barbell kinematic
and kinetic variables were calculated for the success
and failure trials.
16 Biomechanisms 25
Table 3 Definition of kinematic variables in COM
symbol
unit
COM_DxB
definition
Vertical direction variable
COM_Dy3
［m]
Maximum height to the catch
position
COM_pVy+ [m/s]
Maximum upword velocity
COM_pVy- [m/s]
Maximum downword velocity
Horizontal direction variable
COM_% TDx+
［%]
c
Relative height of COM to the
height of the barbell that
normalized by maximum height
at start of moving drop
COM_Dy3
［%]
Relative height of COM to the
height of the barbell that normalized by maximum height at
start of moving forward
COM_Dx2
［m]
Start position to the catch
position
COM_DxB
［m]
COM_DxF
［m]
Start
position
to
most
backward position in the
turnover phase
Most backward position in
turn- over phase to the catch
position
B
A
D
E
COM_Dy1
COM_% TDy-
E: catch position D:
max. barbell height C:
O
2nd knee max. ext.
COM_Dx2 B：1st knee max. flex.
Y COM_DxF
A: 1st knee max. ext.
O: start position
Forward
→
Figure 4 Schematic of COM trajectory during snatch and variables
an
unknown
related to displacement
A paired t-test was used to examine differences.
The Kolmogorov-Smirnov test was used to test the
normality of each variable. The significance level
was set at a risk rate of less than 5%. The effect
size was used as an indicator of the magnitude of
the difference in means.
COM_pVx+ [m/s]
COM_pVx- [m/s]
Maximum
forward
linear
veloci- ty after most backward
position
Cohenʼs d was calculated. The evaluation criteria for the
Maximum backward linear velocity after most backward
position
and 0 . 8-:
The vertical and longitudinal components of the
force acting on the barbell were calculated from the
acceleration and mass of the barbell and the
acceleration of gravity, based on the method of Ikeda
3)
et al.
.
The power acting on the barbell was
calculated for each axis component as the product of
the force acting on the barbell and the velocity.
Based on the definitions shown in Table 3 and
Figure 4, the kinematic variables of COM were
calculated
for
each
of
the
successful
and
unsuccessful trials. To examine the amount of
backward displacement of the body, the negative
displacement of the X-axis component of the toe
between the start and catch positions (backward
displacement) was calculated.
For the joint angle variables, the maximum angular
velocity of the ankle, knee, and hip joint extension
after the start of the 2nd pull phase was calculated.
effect size were 0.0-0.2: trivial,0.2-0.5: small,0.5-0.8: medium,
3.
large13)
.
result
2.5 Statistical Analysis
of the mean value of each variable between
successful and unsuccessful trials.
(�) Biomechanical Study on Success Factors of Snatch in Top Female Weightlifters in Japan 17
F i g u r e 5 shows the barbell trajectories of the
snatches in the successful and unsuccessful
attempts, with the one with the highest lifted weight
for each weight class as a representative example.
The results for all 11 athletes are shown below.
3.1
Barbell Variables
Table 4 shows the results of comparing the
barbell kinematic and kinetic variables between
the successful and unsuccessful snatch attempts.
the amount of forward displacement of the barbell
(Dx3) after the start of the 2nd pull phase was
significantly smaller in the successful attempt than
in the unsuccessful attempt (success: 0.05±)
0.02 m, failure: 0.07±0.02 m, p<0.01, d>0.20).
The X-axis component of displacement between
the most forward position of the barbell and
the catch position during the 2nd pull phase
(DxL) was significantly smaller for successful
trials than for unsuccessful trials (success:
0.13±0.03 m, failure: 0.15±0.04 m, p<0.01,
d>0.50). The maximum forward velocity of the
barbell (pVx
18 Biomechanisms 25
weight category 48 kg weight category 48 kg weight category 53 kg weight category 53 kg
1.2
successful
1.0
unsuccessful
0.8
catch position max.
0.6
barbell height 2nd
0.4
knee max. flex. 1st
knee max. ext. 1st
knee max. ext.
start position
vertical displacement [ m ].
0.2
Forward →
0.0
-0.2
0.0
0.2
-0.2
0.0
0.2
-0.2
0.0
0.2
-0.2
0.0
0.2
-0.2
0.0
0.2
horizontal displacement [ m ].
weight category 58 kg
weight category 58 kg
weight category 58 kg
weight category 63 kg
weight category 69 kg
weight category 69 kg
-0.2
-0.2
-0.2
-0.2
-0.2
-0.2
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.2
0.0
0.0
0.2
0.0
0.2
0.0
0.2
0.0
0.2
0.2
horizontal displacement [ m ].
Figure 5 Comparison of barbell trajectories for successful and unsuccessful snatch attempts (representative example)
(+) was significantly smaller for the successful trials
than for the unsuccessful ones (success: 0.49 ± 0.11
m/s, failure: 0.54 ±
0.13 m/s, p<0.01, d>0.20). The maximum backward
force (pFx-) exerted on the barbell was significantly
greater on successful trials than on unsuccessful
trials (success: -463± 83 N, failure: -482± 83
N, p<0.05, d>0.2
0
) The results of the analysis were
similar for the other variables related to the barbell.
There were no significant differences between the
successful and unsuccessful attempts for the other
barbell variables.
3.2
COM and toe parameters
Table 5 shows the results of the comparison of
the kinematic variables of COM between the
successful and unsuccessful snatch trials. The
value of COM_% TDx+, which indicates
the starting point of COM's forward displacement
relative
to
the
barbell's
raising
height,
was
significantly greater in the successful attempt than in
the unsuccessful attempt (success: 94.02±
(�) Biomechanical Study on Success Factors of Snatch in Top Female Weightlifters in Japan 19
3.25%, Failure: 92.34±3.02%, p<0.05,d>0.50). The X-
axis component of the displacement between the
start and catch positions of the COM (COM_Dx2)
was significantly larger for the successful trials
than for the unsuccessful ones (success:
0.05±0.04 m, failure: 0.00±0.06 m, p<0.01,
d>0.50). The X-axis component of the
displacement of the COM from the rearmost
position to the catch position during the turnover
phase (COM_DxF) was significantly smaller for
the successful trials than for the unsuccessful
ones (0.07±0.02 m for success, 0.10±0.03 m for
failure, p<0.001, d>0.80). pVx+) was significantly
different between the success and failure trials,
with the success trials showing significantly
smaller values than the failure trials (success:
0.34±0.06 m/s, failure: 0.44±0.08 m/s, p<0.001,
d>0.80). The other variables related to COM
included the time between successful and
unsuccessful attempts
20 Biomechanisms 25
Table 4 Comparison of variables related to barbell between successful and unsuccessful attempts
Table 5 Comparison of variables related
to COM between success and f a i l u r e t r i a l s
n=11
unit
successful
unsuccessful
Dy1
［m]
1.21±0.06
1.21±0.06
n=11
unit
Dy2
［m]
1.05±0.05
1.04±0.05
COM_Dy1
Dy3
［m]
0.17±0.02
0.17±0.03
COM_Dy3
pVy+_1st
［m/s]
1.28±0.11
1.27±0.11
COM_pVy+
†
pVy+_2nd
［m/s]
1.93±0.13
1.91±0.12
COM_pVy-
† [m/s] -1.92±0.14 -1.90±0.15
［m/s] -1.92±0.14 -1.90±0.15
COM_% TDy-
unsuccessful
79.49±1.24 79.50±1.18
［m]
0.45±0.03
0.43±0.03
［m]
0.33±0.02
0.33±0.02
［m/s] 1.19±0.07
1.17±0.07
pVy-
［m/s]
-0.87±0.10
-0.87±0.11
pFy_1st
［N]
956±120
946±100
COM_Dx2 **††† [m] 0 . 05±0.04 0 . 00±0.06
pFy_2nd
［N]
1092±129
1082±130
COM_DxB
† [m] 0.12±0.03 0.10±0.03
［m] 0 . 12±0.03 0 . 10±0.03
pPy_1st
［W]
1216±192
1198±164
pPy_2nd
［W]
1843±250
1826±264
pFy% height
［%]
62.3±3.2
62.9±2.3
Dx1
† [m].
0.05±0.02
0.06±0.02
Dx2
† [m].
0.13±0.05
0.14±0.06
Dx3
**† [m].
0.05±0.02
0.07±0.02
COM_% TDx+
†
successful
［%]
COM_DxF *****†††† [m] 0 . 07±0.02 0 . 10±0.03
COM_pVx+ ∗∗††† [m/s] 0.34±0.06 0 . 44±0.08
COM_pVx05
*: p<0.
［m/s] -0.89±0.08 -0.88±0.09
†: d>0.20
mean±S.
D.
01
001
**: p<0.
****: p<0.
DxL **†† [m].
*††† [%] 94.02±3.25 92.34±3.02
††: d>0.50
†††: d>0.80
0.13±0.03
0.15±0.04
m/s].
0.49±0.11
0.54±0.13
pVx-
［m/s]
-0.46±0.08
-0.46±0.09
The analysis was conducted on 11 women's
pFx+
［N]
598±105
612±88
snatches at the Women's World Championships in
*† [N].
-463±83
-482±82
Tokyo, Japan, who had successful and unsuccessful
pVx+
pFx-
**† [
attempts at the same weight and who dropped the
barbell backward in the unsuccessful attempts.
Analysis vs.
05
†: d>0.20
*: p<0.
mean±S.
D.
01
success factors of the snatch in top-class female
††: d>0.50
**: p<0.
The purpose of this study was to determine the
weightlifters in Japan. 2016 All Japan Championships
Large
No significant difference was found in the
The amount of backward toe displacement was
0.10±0.06 m for the successful trials and 0.08±0.05 m
for the unsuccessful trials, with no significant
differences
between
the
successful
and
unsuccessful trials.
3.3
Joint Variables
The maximum angular velocity of extension of the
lower extremity joints after the start of the 2nd pull
phase was compared between the successful and
unsuccessful snatch trials. joint(success:346.4±49.0°/s,
failure: 347.2±49.1°/s).
4. consideration
(�) Biomechanical Study on Success Factors of Snatch in Top Female Weightlifters in Japan 21
The results of the analysis of the barbell
trajectories
and
body
movements
of
the
elephant athletes showed that, among the
hypothesized factors of success in the snatch in
this study, 1) there was no statistical difference in
the relevant variables (variables related to the Y-axis
direction of the barbell) between the success and
failure trials with regard to the barbell raising
height, but 2) the displacement of the barbell and
body in the front-back direction However, for 2)
barbell
and
body
displacement
in
the
anteroposterior direction, the related variables
（ Statistical differences were found between the
successful and unsuccessful trials for the variables
related to the Y-axis direction in the COM for the
barbell and lifter.
4.1
About the Raising Height of the Barbell
Dy1 was statistically
equivalent
between
successful and unsuccessful attempts (Table 4).
This suggests that the barbell was raised high enough
in the failure trials. The variables related to velocity,
force, and power of the Y-axis component of the
barbell, which may affect Dy1, were not significantly
different between the successful and unsuccessful attempts
(Table 4
). Previous studies that analyzed only
successful snatches indicated that the vertical
velocity and power of the barbell in the 2nd
pull phase were important for a successful
snatch14)
. However, in the present study, which
compared successful and unsuccessful snatches,
the variables related to these variables were not
significantly different between successful and
unsuccessful attempts.
22 Biomechanisms 25
The results suggest that the barbell height is not a
trials. In previous studies, it has been shown that reducing
factor that directly affects the success or failure of the
the amount of back-and-forth displacement of the barbell in
Snatch. These results suggest that barbell height is
the snatch is efficient because it reduces the mechanical
not a factor in the success of the snatch. This result
work, and that the amount of back-and-forth
does not support one of the hypotheses of this study,
displacement of the barbell after the start of the 2nd pull
that the barbell height is a factor in the success of the
phase in the
snatch.
Previous studies have pointed out the need to
sneeze under the barbell with a time allowance
during the turnover phase to the catch
Kangwei et al.
16) calculated the
phase7,8,15)
.
barbell height required for
a successful snatch in top-class Asian male
weightlifters based on their attempts during
competition. The values varied by weight class, but
the results were similar in competition. Although the
values varied by weight class, it was shown that a
snatch with a weight close to the maximum lifting
weight handled in competitions required the barbell
to be raised to a height of about 70-77% of the height
of the athlete. However, that study showed the
barbell height in successful snatch attempts only,
and did not compare it to the barbell height in
unsuccessful attempts. Therefore, the barbell height
for the snatch in the previous study may not be the
same as the barbell height required to perform the
snatch successfully. Although the height of the
athletes analyzed in this study is unknown, Dy1 was
statistically equivalent between successful and
unsuccessful attempts within the same athlete,
suggesting that the barbell height in the snatch
reached the minimum height required for success,
even in unsuccessful attempts, among top-class
female lifters in Japan.
4.2
Displacement of the barbell and body in
the front-back direction
Dx3 and pVx+ were significantly smaller in the
successful trials than in the unsuccessful trials.
DxL and pFx- were also significantly smaller in the
success trials than in the failure trials (Table 4). This
indicates that the amount of displacement of the barbell
from the beginning of the 2nd pull phase in the
successful trials was smaller than in the unsuccessful
(�) Biomechanical Study on Success Factors of Snatch in Top
Female
Weightlifters
in Japan
23
cases,
the
barbell was
observed
It has been stated that it is the preferred technique
to "hit" and in other
. Although the present study did
cases, it was observed to "rub up" against the
not examine whether the mechanical efficiency of
barbell. The backward displacement of the barbell
different amounts of barbell displacement affected
indicated by DxL is observed from the turnover
the success or failure of the snatch, it is likely that
phase (Figure 5). The forward displacement of the
the amount of barbell displacement affected the
COM is also observed from the turnover phase
positional relationship between the lifter and
(Figure 4). The turnover phase in the snatch is often
barbell in the catch position and influenced the
referred to as the backswing phase.
of raising the
barbell17)
success or failure of the snatch. Stone et al.
compared the trajectory of the
8)
snatch 8) compared the trajectory
of the barbell between the success and failure
trials, but no statistical differences were revealed.
This may be because they did not categorize the
way the Snatch failed, although the sample size
was large. However, based on the trend of the
trajectory of the barbell in the successful trials, we
proposed the hypothesis that the amount of backand-forth displacement of the barbell affects the
success or failure of the snatch. The results of this
study support this hypothesis.
The
amount
of
forward
and
backward
displacement of the barbell is determined by the
product of the forward and backward forces
acting on the barbell. In the athlete-level snatch,
it is noted that during the 2nd pull phase, when
the greatest force is exerted, the barbell contacts
the base of the hip joint as the lower extremity
joints are extended, and the barbell gains a large
forward
force4)
. Maximum angular velocity of hip
joint extension and maximum forward force
exerted on the barbell
（ The (pFx+) was equivalent between the
successful and unsuccessful trials, but it is
presumed that the way the barbell made contact
with the body affected the forward force product of
the
barbell
and
the
amount
of
forward
displacement. In weightlifting instruction in
Japan, there is a teaching
language
in
which the barbell is placed against the
pubic bone during the 2nd pull phase in order
to pull the barbell
backward3)
. 3) When observing
the snatches analyzed, it was observed that the
barbell actually made contact near the base of
the hip joint in all of the trials. However, in some
24 Biomechanisms 25
with taping. Therefore, during the turnover
in the catch position from the absolute coordinate
phase, the lifter's body is in the air, and there is a
system Dx2 and Dy2 were equivalent between the
period of time when no significant external force
successful and unsuccessful trials, suggesting that the
other than gravity acts on the body-barbell system.
position of the barbell in the catch position was the
In order to backstep, the lifter applies a force
same between the successful and unsuccessful trials.
toward the front of the ground, which causes a
However, between the turnover phase and the catch
backward force to act on the system. Since the
phase, the barbell was pulled backward significantly,
force product of the backward ground reaction
and the front part of the body was moved forward as a
force until just before the release determines the
result.
8,18)
backward momentum of the system during the
dwell period, it can be inferred that the difference
in the amount of backward displacement of the
barbell between the success and failure trials is
due to the way the force is applied to the ground
just before the release by the backstep, i.e.,
during the 2nd pull phase. In this study, the
variables related to the Y-axis component of COM and
the amount of backward displacement (COM_ DxB)
were equivalent between the success and failure
trials, but COM_DxF and COM_pVx+
were significantly smaller for the success trials
than for the failure trials. In addition, COM_% TDx
+ was significantly greater in the success trials
than in the failure trials (Table 5). These results
indicate that the vertical movement of the body under
the barbell to catch the barbell was equivalent
between the successful and unsuccessful trials, but
the time point for the unsuccessful trial was earlier
than that for the successful trial.
（The body initiated the forward movement when the
barbell was in the low position, and the body moved
forward significantly faster. In addition, DxL and
pFx- were greater in the failed attempts than in the
successful attempts. During the dwell period of the
turnover phase, the front-back acceleration of the
barbell and COM showed a bimodal pattern, with the
barbell and COM accelerating backward and forward,
respectively (Figure 6). This suggests that during the
turnover phase, in order to exert a force to displace
the barbell backward, the body was subjected to a
reactionary forward displacement force. Dx2 and
Dy2 were similar between the successful and
unsuccessful attempts, suggesting that the barbell
(�) Biomechanical Study on Success Factors of Snatch in Top Female Weightlifters in Japan 25
The increased forward displacement of the barbell
in the catch position increased the distance
between the barbell and the body in the sagittal
plane, which may have caused the barbell to fall
backward. These results suggest that the amount
of forward displacement of the barbell from the
2nd pull phase to the turnover phase and the
amount of backward displacement of the barbell
and forward displacement of the body from the
turnover phase to the catch phase are factors
that affect the success or failure of the snatch.
4.3
Challenges and Limitations
Because this study compared success and
failure of snatches with the same weight in the
same athlete, the results of this study are not
considered to provide insight into the success of
snatches that exceed the athlete's maximum lifting
weight. In addition, the results presented in this
study were only analyzed when the barbell was
dropped backward. In addition to backward-falling
barbell failures, forward-falling barbell failures are
also common in the snatch. If excessive emphasis
is placed on movements to keep the barbell from
falling backward in the snatch, the amount of
backward displacement of the barbell or the amount of
forward displacement of the body may be insufficient, leading
to a failure in which the barbell falls forward. Therefore, it is
expected that a similar analysis of the failure to drop the
barbell forward will provide more insight into the factors
that contribute to the success of the snatch.
5.
summary
The
purpose
of
this
study
was
to
use
biomechanical methods to determine the success
factors of the snatch in top-class female weightlifters
in Japan. The snatches of 11 athletes who dropped
the barbell backward in failure were included in the
analysis. Kinematic and kinematic variables of the
barbell in the sagittal plane, kinematic variables of
the COM, and lower limb joint motion were
analyzed between success and failure attempts.
26 Biomechanisms 25
Displacement [ mm ].
a
15
c
d
e
Toe_Y
10
5
0
10
Barbell_X
0
[ m/s ]2
Acceleration
b
-10
COM_X
0
[ m/s ]2
Acceleration
10
-10
0.0
0.2
0.6
0.4
0.8
1.2
Time [ s ]. 1.0
Figure 6 Typical examples of toe height, barbell and COM acceleration of the anterior-posterior
component of a failed attempt. a, b, c, d and e indicate the 1st pull, transition, 2nd pull, turnover and catch
phases, respectively. The △ in the stick picture indicates the toe position at the start of raising the barbell.
The results of the comparison of the snatches with
with the cooperation of the Japan Weightlifting
weights below the athlete's maximum lifting weight
Association and those involved in the operation of the
suggested the following factors for the success of the
competitions.
snatches with weights below the athlete's maximum
lifting weight.
(l) Variables related to vertical displacement of
the barbell, maximum velocity, force and
power are not success factors for the snatch.
(2) The amount of backward displacement
of the barbell from the 2nd pull phase to the
catch phase and the behavior of the body's
forward
displacement
from
the
turnover
phase to the catch phase are two of the
success factors of the snatch.
thanks
The recording of lifting movements at the
competition venue for this study was made possible
(�) Biomechanical Study on Success Factors of Snatch in Top Female Weightlifters in Japan 27
The implementation of the project has been
successful. We would like to express our gratitude.
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(�) Biomechanical Study on Success Factors of Snatch in Top Female Weightlifters in Japan 29
Biomechanical Comparison of Successful
and Unsuccessful Snatches
in Japanese Top-class Female Weightlifters
Hideyuki NAGAO1 , Yasuyuki KUBO1 , Zhong HUANG2 , Yoshitaka
MORISHITA 11 Japan Institute of Sport Sciences,2 Sports Okinawa
Abstract The purpose of this study was to clarify the success factors of snatches in elite Japanese female
weightlifters from the viewpoint of biomechanics. The data in this study included successful and
unsuccessful (due to a backward barbell drop) snatch lifts achieved using the same weights by the same
lifter. The data in this study included successful and unsuccessful (due to a backward barbell drop) snatch
lifts achieved using the same weights by the same lifter. The results revealed significant differences in the
barbell backward and forward displacement and forward peak velocity, which were significantly The
results revealed significant differences in the barbell backward and forward displacement and forward peak
velocity, which were significantly smaller in a successful snatch lift than in an unsuccessful lift (p<0. 01).
The COM forward displacement and forward peak velocity in a successful snatch lift were significantly
smaller than in an unsuccessful lift (p<0. 01). Furthermore, there was no significant difference in the
maximum barbell height between successful and unsuccessful lifts. Based on these findings, we concluded
that maximum barbell height is not a success factor for snatches in elite female Japanese weightlifters.
Decreased barbell forward and backward displacement in the second pull phase to catch each phase and
decreased COM forward displacement during drop under the barbell increase the probability of success
without a backward displacement. Decreased barbell forward and backward displacement in the second
pull phase to catch each phase and decreased COM forward displacement during drop under the barbell
increase the probability of success without a backward barbell drop in the snatch motion.
Key Words：Weightlifter, Motion analysis, Barbell trajectory