THE EFFECT OF KICKING DIRECTION ON SOCCER INSTEP KICKING KINETICS
1Koichiro Inoue, 2 Hiroyuki Nunome, 3 Hiornari Shinkai and 2 Yasuo Ikegami
Graduate School of Education and Human Development, Nagoya University, Japan
2Research Centre of Health, Physical Fitness and Sports, Nagoya University, Japan
3
Faculty of Education, Art and Science, Yamagata University, Japanemail: k.inoue@nagoya-u.jp

1SUMMARY
Instep kicking is a fundamental technique in soccer. In match
situation, players have to kick the ball to various directions.
Although several studies focused on such conditions, Kineticparameters, such as joint torque, has not been clarified. The
purpose of this study, therefore, was to illustrate the effect ofkick directions on soccer instep kicking kinetics. Nine
experienced male soccer players performed instep kicks onthree conditions to change the kicking directions (15, 45 and75 degrees to the kicking direction). Their kicking motions
were captured using electrically synchronized four high-speed
video cameras at 250Hz. Three dimensional joint torque andangular velocity of swing leg (hip and knee) were calculated.
The general patterns of joint torque and angular velocity weresimilar during each condition (AP15, AP45, and AP75).
Absolute foot velocity at immediately before ball impact was
sufficiently accelerated, and has not significant differences
during three conditions. It was suggested that players whoparticipated in this study achieved a well-coordinated kicking
motion, even if they were required peculiar technique to kickto angled direction. In addition, player kicks the ball to angled
direction, larger hip addiction torque act to control the hipabduction motion.

INTRODUCTION
Instep kicking is a fundamental technique in soccer. Previousstudies have examined three dimensional motions of thatkicking, and the kinetic parameters of the swing leg have beenclarified [4,5]. However, these studies exclusively focused on
the motion when the player kicks the ball to one certain
direction (towered goal). In match situation, players have tokick the ball to various directions. Changing those directionsis attributed to change the angle between approach and kicking
direction. Although several previous studies have examinedthe effect of approach angle on soccer instep kicking [2,3,6],
the three dimensional kinetics, such as joint torque, have neverbeen investigated. The purpose of this study was to illustrate
the effect of kick directions on soccer instep kicking kinetics.
METHODS
Nine experienced Japanese male soccer players (hight :172.4±6.5 cm, weight : 62.3±5.9 kg, age : 19.4±0.7 year,career : 11.6±2.8year) were volunteered to participate in thisstudy. They performed instep kicking using their preferred leg(All subject preferred right leg) on three conditions to change

the kicking directions. Those three conditions were decided toangle between kick direction and approach directions (15, 45and 75 degrees; Here after AP15, AP45 and AP75,respectively). The three conditions were performed in arandomized order. Furthermore, each subject was instructed tokick with maximum effort, toward the center of target(0.8m×0.8m), which placed at 3m ahead. Their kicking
motions were captured using electrically synchronized fourhigh-speed video cameras at 250Hz. A digitizing system wasused to digitize manually skin markers, which were attached
to several body landmarks. The three dimensional coordinateof each markers was reconstructed using the direct linertransformation (DLT) method.
Angular velocity of right lower leg (foot and shank), rightthigh and pelvis were calculated from local reference frames
fixed on each segment. According to the procedures applied in
the previous studies [1,4,5], joint torques (hip extension/flexion, adduction/abduction, internal/external rotation, knee
extension/flexion, internal/external rotation) were computed
using two link segment model composed with the lower legand thigh.
The time-series data were digitally smoothed by a forth- order
Butterworth filter at 12.5Hz. To avoid systematic distortiondue to ball impact, subsequent data of impact was extrapolated
before smoothing and then extrapolated region was removed
after smoothing. Finally kick motion from the toe of thekicking (right) leg to ball impact was normalized to 100% [4].

RESULTS AND DISCUSSION
There was no distinct change for the changing patterns ofsegmental angular velocities in all conditions (AP15, AP45,and AP75). Likewise, the general patterns of joint torque(figure 1, 2) were also similar between the conditions. During
kicking (from toe off to ball impact), hip flexion, addiction,external rotation, knee extension torques
were mainlyappeared. The change of knee internal/external rotation torquewas small enough to be negligible. Those results almost
correspond to those in previous studies regarding the normal
instep kick towered goal (did not instruct approach angle)[4,5]. It was indicated that kicking direction had noappreciable influence on the general exerting pattern of hipand knee joint torque. Previous study focused on difference
between of prefer leg and non-prefer leg, and had been
discussed the mechanism for accelerating the lower leg ofswing leg [5]. This result was concluded that if players alreadyachieve a reasonable inter-segmental coordination, themuscular force (knee extension muscle torque) would be themain determinant for the faster leg swing. In present study,
although the peak magnitude of knee extension torque (muscletorque) was significantly lower in the AP75 than that in theAP15, no significant differences were observed between thetwo conditions for the absolute foot velocity immediately
before ball impact (AP15: 18.4±1.0 m/s & AP75: 18.8±0.9m/s). From these results, it was suggested that players whoparticipated in this study achieved a well-coordinated kicking
motion, even when they were required to kick the ball to very
angled direction.
Nunome et al. [4] suggested that the hip adduction torqueprobably acts to control the hip abduction which is produced
the motion dependent interactions produced by an angled
approach run and pelvis rotation. In the present study, thelarger kicking angle, the higher angular impulse of hipabduction (AP15: 8.3±2.8 Nm ･ s, AP45: 10.1±2.6 Nm ･ s
AP75: 12.1±3.1 Nm･s) was indicated, and the peak of theAP75 was significantly higher than that in the AP15. Faster
pelvic rotation was used by players when they kickthe ball to large angled direction. This motion likely
facilitates the body to face the kicking direction,
thereby emphasizing the centrifugal force acting on
the swing leg. It was assumed that the larger hipadduction angular impulse observed in AP75 has a role tomaintain the swing leg angle against the centrifugal force.

CONCLUSION
The present study clarified the joint torque of swing leg toillustrate the effect of kick directions on soccer instep kicking
kinetics. Kicking direction doesn’t exert general pattern of hipand knee joint torque. As player kick the ball to angled
direction, larger hip addiction torque act to control the hipabduction motion.
Figure 2: Changes in the joint torque of hip (top:flexion/extension, middle: addiction/abduction, bottom:internal/external rotation). Line with marker( ● , ◆ , ▲ )indicated AP15, AP45, AP75, respectvely.

Figure 1: Changes in the joint torque of knee
(extention/frexion). Line with marker ( ● ,◆ ,▲ ) indicatedAP15, AP45, AP75, respectvely.

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