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６．背負投の崩し・作り局面における引き力と床反力のタイミング

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６．背負投の崩し・作り局面における引き力と床反力のタイミング
カリフォルニア州立大学サクラメント校
カリフォルニア州立大学サクラメント校
東京学芸大学今村 Rodoney
Daryl.L.Parker
射手矢岬

６．Timing Characteristics of Pulling Force and Ground
Force During Kuzushi and Tsukuri Phases of Seio-nageRodney IMAMURA
Daryl.L. PARKER
Misaki ITEYA要（California State University Sacramento）（California State University Sacramento）（Tokyo Gakugei University）

約

本研究の目的は背負投の「崩し・作り局面」における取の引き手速度と床反力の関係を明らかにすることであった．被験者は熟練者（有段者）１名と非熟練者（無段）１名で，それぞれ背負投を行った．受は熟練者（有段者）１名で両方の被験者の背負投を受けた．２台のビデオカメラ（60Hz）はLEDで同期され，三次元分析のためにDLT法による三次元動作解析システムが用いられた．取の引き手の手首の速度と受の重心速度が測定され，技能レベル間において崩し･作り局面におけるそれらの効果を比較した．背負投施技中のタイミングを比較するために，両被験者の時間は崩し・作り局面を100％となるように標準化された．結果は以下のとおりであった．
取の手首の速度と受の重心速度は熟練者において大きな値であった．床反力を推定するためにみた足の床への接地は手首の２か所の最大速度と関係していたが，これは引き手のパワーと床反力の関係を示すものであった．熟練者の手首の速度ピークは最初の足の踏み込みと同時であったが，非熟練者は手首の速度ピークは第１歩の足の床接地後であった．これらのデータから足の床への接地は引き力と関係し，引き力と床接地のタイミングは技能レベルやパフォーマンスの指標となる可能性が示唆される．

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Introduction
Kodokan judo categorizes throwing techniques into phases, each according to the purpose orfunction of movement. The kuzushi phase is characterized by the thrower’s（tori’s）attempt
to break the opponent’s（uke’s）balance prior to throwing. The tsukuri phase directly follows
kuzushi and is characterized by tori ﬁtting the throw into uke. The kake phase is the ﬁnal phasecharacterized by the throw itself. Phase classiﬁcation was developed for the purpose of analyzing
judo from a scientiﬁc basis. Thus, using phases is a logical and appropriate method for studying
the biomechanics of judo throwing techniques.
Studies have attempted to explain the basis of phase descriptions to a certain degree.
Kinematic studies have investigated the center of mass（COM）movement of uke and tori during
various phases. Imamura et al.（2006）measured COM velocity of uke during kuzushi and founda resistance to tori’s efforts. This resistance pattern by uke was thought to be necessary for
tori to create an effective fit-in during tsukuri. Imamura et al.（2007）performed a similar
study with COM comparing harai-goshi under simulated and competitive situations. They foundpossible precursors to the ippon throw by looking at the movements of both tori and uke. The
study also found diﬃculty in determining a clear diﬀerence between kuzushi and tsukuri phases,
particularly during the competitive condition. Ishii et al.（2005）analyzed COM positions of uke
precluding an ippon score（i.e. kuzushi/tsukuri phases）during competition for the throw osotogari. They also found possible precursors to ippon by looking at uke’s position of COM relative
to their base of support. The previous studies demonstrate similarities in their attempt to deﬁne
the ideal circumstances prior to a successful throw and further deﬁne the importance of kuzushi
and tsukuri.
Under basic physical law, movements must have an origin of force. For humans and judo
players alike this force is generated from the contraction of muscle. The contraction of muscle,in turn, is composed into ground reaction forces（GRF）which allows the body to accelerate andmove. With this in mind, a number of studies have measured the GRF of tori during judo throws（Tezuka et al. 1983; Harter and Bates, 1985; Pucsok et al. 2001）. In terms of phases, Harterand Bates（1985）described a GRF pattern for the harai-goshi throw consistent with the original
phase descriptions by Kodokan judo. They found a pull-push-pull GRF pattern which seemed tomirror the intent of kuzushi（pulling uke oﬀ-balance）, tsukuri（pushing into uke or ﬁtting-in），and kake（pulling uke once more to throw）. Although the phases were not directly addressed
during this study, it shed light on the biomechanical purpose of tori’s actions from a force
generating perspective.
The purpose of this study was to continue investigations into the deﬁnition of throwing phasespresented years ago by Jigoro Kano. The study also seeks to identify possible biomechanicalmarkers that precede an ideal throw by combining concepts of body movement（kinematics）
and body force generation from the ground（kinetics）.

Specifically, the study serves as apreliminary investigation to the relationship between tori’s pulling force and ground force during
the kuzushi/tsukuri（KT）phase of the throw seio-nage.

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Methods
One advanced（black belt）subject and one novice（white belt）subject served as the tori forthis study. A single advanced subject（black belt）was used as the uke and accepted the throw for
both subjects. Information including age, weight, and height were collected for all subjects（Table1）. Each tori subject performed the seoi-nage throw（hand throw）from the right-handed
position. To ensure an adequate combination of maximal eﬀort and proper technique, the subjects
were required to perform the throw with maximal eﬀort while maintaining their balance（stayingon at least one foot and no more than one hand touching the ground）throughout the entire throw.
This procedure was designed to simulate a perfect throw with no conscious resistance fromuke.
Table 1. Subject Information
表１．被験者の特性

SubjectWeight (kg)Height (m)AgeAdvancedNovice

89
90

1.78
1.80

32
20

Rank(Degree Black)3dan (3rd)White Belt

Uke

89

1.75

38

4dan (4th)

Two video cameras（JVC 60 Hz）synchronized by LED were used to collect the data. Thecameras were positioned approximately 45 degrees apart facing one side of uke and tori so thata sagittal view of the action was seen. Directions for the throw were set such that uke always
began each trial facing the positive x（anteroposterior）direction and his right shoulder facing
the positive z（mediolateral）direction. This process insured that uke was always thrownpredominantly towards the positive x direction with his right shoulder initially facing the positivez direction. The upward direction was designated as positive y（vertical）for all throws.
A three dimensional motion analysis system（Peak Performance Technologies, Inc.,
Englewood, CO）and the DLT（Direct Linear Transformation）procedure were used to analyze
three-dimensional kinematic data. Since judo requires that all participants wear a judo uniform（judo gi）, joint markers could not be used. Therefore, manual digitization of 18 body points forboth tori and uke were performed by a single digitizer for both trials. The digitized data weresmoothed using a 4th order zero lag Butterworth ﬁlter with a cut-oﬀ frequency set by the Peaksoftware optimization technique. COM calculations were based on anatomical parameters from
Clauser et al.（1969）.
Throwing phases were based upon Kodokan instructional literature（Kano, 1986）. In lightof the diﬃculties in determining the dividing point between kuzushi and tsukuri（Imamura et al.
2007）, this study combined the two phases into one with the understanding that kuzushi always
precedes tsukuri. Thus, the kuzushi/tsukuri（KT）phase for the seoi-nage throw began withthe ﬁrst movement towards the entrance of the throw by tori, followed by the placement of tori’s

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feet to the ground, and ended when uke’s heels began to rise from the ground. The KT phase isillustrated in Figure 1.

Figure 1. Three pictures describing the sequence of kuzushi/tsukuri（KT）for seio-nage:
1）tori’s initial forward movement, 2）tori’s two feet contact, 3）uke’s heel lift.
図１．３つの図は背負投の崩し・作り局面を表している．
１）取の最初の前方への動き，２）取の両脚支持，３）受の踵の浮上

Tori’s pulling wrist velocity and uke’s COM velocity were measured to analyze the eﬀectivenessof kuzushi and tsukuri between skill levels. Time for both subjects was normalized such that
the KT phase constituted 100% of total time. This was done to compare timing characteristics ofwrist velocity and foot contact between subjects of diﬀerent skill level.

Results
As expected, the advanced player created greater peak wrist velocity in all three directions ofpull during the KT phase. The direction of pull pattern was the same for both subjects, the wrist
velocities occurred forward（positive x）, to uke’s right（positive z）, and upward（positive y）.
The peak velocity of uke’s COM was greater for the advanced subject for the x and z directions
but not for the y direction. The pull pattern of peak wrist velocity mirrored that of uke’s COM
peak velocity. The data indicated that uke’s body moved forward, to their right, and upward.
The instant of foot contact with the ground served as an inference to GRF contribution. For
the advanced subject the ﬁrst foot contact occurred at 57% of the KT phase, while the second
foot contact occurred at 85%. For the novice subject the ﬁrst and second foot contact occurredat 33% and 85% of KT, respectively. The total KT phase time was similar at 1.15 seconds forthe advanced subject and 1.16 seconds for the novice subject. Table 2 illustrates the peak wrist
velocities for tori and peak COM values for uke as well as the percentage of occurrence within theKT phase.
In terms of timing, peak resultant（r）wrist velocity occurred near the ﬁrst foot contact for
both subjects（Table 2）. The advanced player’s wrist velocity occurred almost simultaneouslywith the ﬁrst foot contact at 56% and 57% of KT, respectively. The novice had disparity between

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Table 2. The following table describes tori’s peak wrist velocity（m/s）and uke’s peak
COM velocity（m/s）for the forward（x）, upward（y）, and uke’s right（z）directions.
Also listed are the occurrences of each velocity as a percentage of total kuzushi/
tsukuri（KT）time.
表２．前方（X），上方（Y），受の右側（Z），３方向の合成（r）における取の手首の最大速度と受の重心の最大速度，およびその時の崩し・作り局面の時点（％）を示した．

Wrist xWrist yWrist zWrist r

COM x

COM y

COM z

COM r

3.05

3.41

1.95

4.54

0.64

0.15

0.44

0.78

% KT

5855

86

56

72

94

72

72

Novice

1.23

1.66

1.25

2.02

0.36

0.2

0.38

0.47

%KT393554

41

81

10090

90

Advancedwrist velocity and foot contact time at 41% and 33% of KT, respectively. The second highest rwrist velocity occurred near second foot contact for the advanced subject at 86% and 85% of KT,respectively. The novice, on the other hand, demonstrated disparity with the second highest
wrist velocity occurring at 54% of KT compared to the second foot contact at 85% of KT. Figure
2 illustrates peak r wrist velocity relative to the first and second foot contacts within the KT
phase.
（ｍ/s）
Second F.CFirst F.C

050100 （％）

Figure 2. The graph illustrates the peak resultant（r）velocity（m/s）of the wrist for theadvanced player（dashed line）and the novice player（solid line）. Markers also
describe the ﬁrst and second foot contact for each subject.
図２．熟練者と非熟練者の手首の最大合成速度．グラフ上のマークは最初の足の床接地と２歩目の足の床接地を表している．

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Discussion
It was the intention of this study to provide preliminary data for analyzing the relationshipbetween tori’s pulling force and ground force during the kuzushi/tsukuri（KT）phase of thethrow seio-nage. It was hypothesized that tori’s pulling force would be directly related to groundreaction forces（GRF）created by the feet. While GRF was not measured in this study, it wasassumed that foot contact with the ground created GRF necessary to create pulling force.
The results indicated differences in pulling force between skill level. The advanced subject
demonstrated larger peak wrist velocity in all three directions of pull. The directions of pull
were the same between subjects with both pulling uke forward, to the right, and upward. Uke’s
peak COM velocity was also larger for the advanced subject and occurred in the same directions
as the wrist velocities for both subjects. For the most part, the results were predictable as
they indicated that both subjects were executing the same throwing technique but with diﬀerent
pulling force magnitudes. It was interesting, however, that both subjects executed the KT phaseat similar speeds（1.15 s for advanced versus 1.16 s for novice）. Thus, the novice subject wasable to execute the KT phase with the same speed as the advanced subject but with much lessforce from the pulling hand and less force onto the body of uke.
There was also a timing diﬀerence between foot contact and peak wrist velocity between skill
level. The advanced subject created the highest and second highest wrist velocities almost
simultaneously with both their ﬁrst and second foot contacts, respectively. The novice player, on
the other hand, demonstrated a time diﬀerence between both foot contacts and the two highest
wrist velocities. The highest wrist velocity occurred later than the ﬁrst foot contact, while thesecond highest wrist velocity occurred much sooner than the second foot contact. Assumingthat the advanced subject is mechanically more eﬃcient than the novice subject, the data indicatethat there is a link between the timing of foot contact（GRF）and wrist velocity（pulling force）.
Because both wrist velocities and COM velocities for uke were much larger for the advanced
subject, it can be assumed that the GRF plays a key role in the generation of pulling force.
There is also an indication that a greater time diﬀerence between GRF and wrist velocity can bedetrimental to an eﬀective pulling force. As stated earlier the advanced subject was able to createthe highest wrist velocities at the point of contact for both feet, while the novice demonstrated
disparities between foot contact and wrist velocity for both feet. Thus, the timing of GRF
production and how it may contribute to pulling force looks to be an advanced skill. In terms ofphase analysis, the ﬁrst foot contact is likely responsible for the function of kuzushi or breaking
uke’s balance. Since the novice subject demonstrated a lag between the ﬁrst foot contact andpeak wrist velocity, it is possible that the subject has not developed the skill to time GRF properlywith pulling force and eﬀectively execute kuzushi.

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Conclusion
An obvious limitation to this study is the lack of GRF data from a force plate. Direct GRF
measurements would determine whether or not the novice subject’s deﬁciencies in pulling force
stem from timing issues, deﬁcient GRF production, or a combination of both. Thus, future studies
should incorporate GRF measurements from a force plate in conjunction with kinematic analysis.
Overall, this study demonstrated possible a link in the timing of GRF and pulling force generated
by tori during KT. Likewise, this timing can be considered a possible indicator of skill level andprecursor to an eﬀective throw.

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