Hiroyuki Nunome

The biomechanics of kicking in soccer: A review

Abstract Kicking is the defining action of soccer, so it is appropriate to review the scientific work that provides a basis of our understanding of this skill. The focus of this review is biomechanical in nature and builds on and extends previous reviews and overviews. While much is known about the biomechanics of the kicking leg, there are several other aspects of the kick that have been the subject of recent exploration. Researchers have widened their interest to consider the kick beginning from the way a player approaches the ball to the end of ball flight, the point that determines the success of the kick. This interest has encapsulated characteristics of overall technique and the influences of the upper body, support leg and pelvis on the kicking action, foot–ball impact and the influences of footwear and soccer balls, ball launch characteristics and corresponding flight of the ball. This review evaluates these and attempts to provide direction for future research.

Segmental dynamics of soccer instep kicking with the preferred and non-preferred leg

Abstract Detailed time-series of the resultant joint moments and segmental interactions during soccer instep kicking were compared between the preferred and non-preferred kicking leg. The kicking motions of both legs were captured for five highly skilled players using a three-dimensional cinematographic technique at 200 Hz. The resultant joint moment (muscle moment) and moment due to segmental interactions (interaction moment) were computed using a two-link kinetic chain model composed of the thigh and lower leg (including shank and foot). The mechanical functioning of the muscle and interaction moments during kicking were clearly illustrated. Significantly greater ball velocity (32.1 vs. 27.1 m · s−1), shank angular velocity (39.4 vs. 31.8 rad · s−1) and final foot velocity (22.7 vs. 19.6 m · s−1) were observed for the preferred leg. The preferred leg showed a significantly greater knee muscle moment (129.9 N · m) than the non-preferred leg (93.5 N · m), while no substantial differences were found for the interaction moment between the two legs (79.3 vs. 55.7 N · m). These results indicate that the highly skilled soccer players achieved a well-coordinated inter-segmental motion for both the preferred and non-preferred leg. The faster leg swing observed for the preferred leg was most likely the result of the larger muscle moment.

Impact phase kinematics of instep kicking in soccer

Abstract The purpose of this study was to capture the lower limb kinematics before during and after ball impact of soccer kicking by examining the influence of both sampling rate and smoothing procedures. Nine male soccer players performed maximal instep kicks and the three-dimensional leg movements were captured at 1000 Hz. Angular and linear velocities and accelerations were determined using four different processing approaches: processed using a modified version of a time-frequency filtering algorithm (WGN), smoothed by a second-order low-pass Butterworth filter at 200 Hz cut-off (BWF), re-sampled at 250 Hz without smoothing (RSR) and re-sampled at 250 Hz but filtered by the same Butterworth filter at 10 Hz cut-off (RSF). The WGN approach appeared to establish representative kinematics, whereas the other procedures failed to remove noisy oscillation from the baseline of signal (BWF), lost the peaks of rapid changes (RSR) or produced totally distorted movement patterns (RSF). The results indicate that the procedures used by some previous studies may have been insufficient to adequately capture the lower limb motion near ball impact. We propose a new time-frequency filtering technique as a better way to smooth data whose frequency content varies dramatically.

The effect of muscle fatigue on instep kicking kinetics and kinematics in association football

Abstract The aim of this study was to examine the effect of leg muscle fatigue on the kinetics and kinematics of the instep football kick. Fatigue was induced by repeated, loaded knee extension (40% body weight) and flexion (50% body weight) motions on a weight-training machine until exhaustion. The kicking motions of seven male players were captured three-dimensionally at 500 Hz before and immediately after the fatigue protocol. The significantly slower ball velocity observed in the fatigue condition was due to both reduced lower leg swing speed and poorer ball contact. The reduced leg swing speed, represented by a slower toe linear velocity immediately before ball impact and slower peak lower leg angular velocity, was most likely due to a significantly reduced resultant joint moment and motion-dependent interactive moment during kicking. These results suggest that the specific muscle fatigue induced in the present study not only diminished the ability to generate force, but also disturbed the effective action of the interactive moment leading to poorer inter-segmental coordination during kicking. Moreover, fatigue obscured the eccentric action of the knee flexors immediately before ball impact. This might increase the susceptibility to injury.

Ball impact dynamics of instep soccer kicking.

PURPOSE The purpose of this study was to reveal the foot-ball interaction during ball impact phase of soccer instep kicking. METHODS Eleven soccer players performed maximal instep kicks. The behavior of kicking foot and ball during ball impact was captured using two ultrahigh-speed cameras at 5000 Hz. Foot motion was described three dimensionally, and the motion of the center of gravity of the ball (CGB) was estimated by the spherical shell model in which the ball deformation was taken into account. The peak ball reaction force acting on the foot was estimated from Newtons equation of motion in which the peak CGB acceleration in sagittal plane was calculated from its velocity slope near the peak ball deformation. RESULTS During ball impact (9.0 +/- 0.4 ms), the foot was passively abducted and everted. Moreover, an unknown feature--slight dorsal flexion before distinctive plantarflexion--was quantified in most trials. The CGB velocity exceeded that of the foot when the ball was maximally deformed (6.2 +/- 0.6 cm). The magnitude of peak ball reaction force reached 2926 +/- 509 N, which corresponds to approximately twice as that of the mean force (1403 +/- 129 N). From the changes of the foot velocity, the CGB velocity, and the ball deformation, the ball impact phase can be divided into four phases. CONCLUSIONS The ultrahigh-speed video and methodology in this study documented complex three-dimensional foot motions to impact in soccer instep kicks, dynamic foot-ball interaction, and larger peak ball reaction force on the foot that previously estimated. It can be considered that effectual duration to accelerate the ball is roughly three fourths of visually determined ball contact time.

Dynamics of the support leg in soccer instep kicking

Abstract We aimed to illustrate support leg dynamics during instep kicking to evaluate the role of the support leg action in performance. Twelve male soccer players performed maximal instep kicks. Their motions and ground reaction forces were recorded by a motion capture system and a force platform. Moments and angular velocities of the support leg and pelvis were computed using inverse dynamics. In most joints of the support leg, the moments were not associated with or counteracting the joint motions except for the knee joint. It can be interpreted that the initial knee flexion motion counteracting the extension joint moment has a role to attenuate the shock of landing and the following knee extension motion associated with the extension joint moment indirectly contributes to accelerate the swing of kicking leg. Also, appreciable horizontal rotation of the pelvis coincided with increase of the interaction moment due to the hip joint reaction force on the support leg side. It can be assumed that the interaction moment was the main factor causing the pelvis counter-clockwise rotation within the horizontal plane from the overhead view that precedes a proximal-to-distal sequence of segmental action of the swing leg.

The continuous measurement of the springboard reaction force in gymnastic vaulting.

Abstract A new method was established for the continuous measurement of force applied from a springboard to a gymnast in vaulting (board reaction force). Male gymnasts performed a handspring vault using a springboard mounted on force platforms. A high-speed video camera sampled the springboard motion at 500 Hz. The springboard was initially partitioned into 29 segments. The force due to the accelerative motion of the springboard was determined by summing the forces of the individual segments. The board reaction force acting on the gymnast was calculated by subtracting the force due to the accelerative motion of the springboard and weight from the force recorded by the force platform. The new method succeeded in illustrating transient changes of the board reaction force. The horizontal and vertical components of the peak values of the board reaction force were three and two times greater respectively than the average values. A series of tests was conducted to determine whether the number of segments of the springboard model could be reduced without affecting accuracy. A model consisting of only four segments produced almost the same accuracy as the 29-segment model. The simplified model is recommended as a more efficient method to measure board reaction force.

Part I: Biomechanics

The motion analysis of kicking in football has been studied by several investigators. However, there are few studies of the interaction of the kicking foot and ball at impact. The purpose of this study is to clarify the relation between the stress distribution, the deformation and the impact point on the foot using the high-speed VTR camera system and the finite element method. The impact process of kicking a ball was analysed to obtain the fundamental data for computer simulation using a highspeed video camera running at 4500 Hz. Six university football players participated. The players kicked a ball with the instep towards a mini-football goal 4 m away. The high-speed video camera was set up 1.5 m away from the impact perpendicular to the motion of the ball. The basic leg shape was constructed using a 3D digitizer. The 3D construction was meshed using MSC/PATRAN (MSC.Software Corporation) through an IGES file. The basic shape of the finite element skeletal foot-joint model was also described using a commercial foot skeletal model for computer graphics and anatomical data, and the solid model was defined after simplifying that model. The hard tissue parts of this foot model consisted of 23 bone models such as the calcaneus, matatarsal, etc., and the soft tissue parts that were modelled consisted of 15 joint models such as the talocalcaneus (subtalar) joint, calcaneocuboid joint, etc. The ligaments and retinacula were not geometrically represented; consequently, the stiffness of the soft tissue parts was estimated including the function of the ligaments and retinacula. The kicking leg and the surface of the ball model were described by a Lagrangian frame of reference and itemized by the finite element method. The air inside the ball was described with a Eulerian frame of reference and quantified by the finite volume method. During the analysis of an impact force, the initial speed in the horizontal direction (25 m s) was assumed for the entire part of the kicking leg in both models. The generation of spin depends upon the impact point of the foot on the ball in relation to the axis of the ball. This impact distance was set at 40 and 80 mm from the ball’s axis and simulation was carried out for coefficients of friction between 0 and 1.0 at intervals of 0.2. Further simulations were carried out with a fixed coefficient of friction of 0.4 with impact distances from the axis of the ball 7150 to + 150 mm at intervals of 20 mm. The model shows reasonable agreement with the experimental data, particularly in the first half of the impact. The ball deformed to 85% of its original diameter in the model compared with 86% experimentally. It was considered that the model matched the experimental data sufficiently to warrant its use for further study. The experimental results from the high-speed video camera showed that the mean of the contact distances was 0.147 m and the contact of the ball and instep was finished before the instep moved the same distance as the ball diameter (about 0.223 m). From the computer simulations, it was noted that even if the kinetic coefficient of friction is equal or nearly equal to 0, rotation of the ball occurs, though it is axiomatic that the spin of the ball increases with the increase in the kinetic coefficient of friction in both simulations. It seems that a large deformation appeared during the impact of the ball and that causes the rotation due to the impact force. Overall, it is considered that the offset distance affects ball spin more than a coefficient of friction. It is suggested that the optimum offset distance is related to a trade-off between ball rotation and ball speed. The peak value of the horizontal impact force in the instep kick was 2439 N, that of the vertical impact force was 853 N, and that of the lateral impact force was 7452 N. On the other hand, the peak value of the horizontal impact force for the ‘infront curve’ kick was 2206 N, that for the vertical impact force was 1221 N, and that for the lateral impact force was 71143 N. It appears that the vertical and lateral forces are concerned with the force that increases the rotation of the ball as well as the flight of the ball in a direction different from the swing direction of the kicking leg. In the computer simulation using the finite element skeletal foot model, the deformation of the foot joint in the lower impact case was larger than that of upper impact case. It is suggested that the energy dispersion of the foot in the lower impact case was larger than that of upper impact case. Journal of Sports Sciences, 2004, 22, 485–593

Myth and fact of ball impact dynamics in football codes

Kicking is important in all the football codes and impact is the most crucial component of the skill. However, only a few studies have documented the foot to ball impact phase adequately due to low sample rates and methodological issues. This paper reviews these studies in an attempt to better understand foot-ball impact and explores the veracity of impact-related coaching cues. In soccer, the use of ultrahigh-speed video, a new smoothing procedure and ball modelling to calculate the centre of mass of the ball during deformation has allowed for detailed analysis of impact. A number of studies have identified four phases during foot-ball contact. First the foot acts to deform the ball (phase I), followed by ball acceleration until foot and ball speeds are similar (phase II). The ball then begins to reform while still accelerating (phase III). The last phase shows little interaction between foot and ball suggesting no influence on ball speed. Also using ultrahigh-speed video in the punt kick, but with methods largely focusing on average rather than instantaneous analyses of impact, differences in impact characteristics have been found between seniors and juniors, preferred and non-preferred legs, and kick distances and kick types. The four phases evident in soccer kicking were also present in the punt kick and might have similar underlying mechanisms. Differences exist between player perceptions of what is happening at impact and what actually occurs. Coaching advice to extend the time in contact to produce greater ball velocity was not correct but maintaining a firm foot in the punt kick for distance is an appropriate cue. Further, impact phase analysis has been shown to have useful practical applications. A unique impact location on the foot was found in producing a knuckle ball, and using the difference between this and the instep kick as a cue, the technique was successfully learned by a university level player. Finally footwear design to improve resultant ball performance was explored, looking at existing footwear products, application of ball to foot impact research and potential theories applicable to footwear.

Primary mechanical factors contributing to foot eversion moment during the stance phase of running

ABSTRACT Rearfoot external eversion moments due to ground reaction forces (GRF) during running have been suggested to contribute to overuse running injuries. This study aimed to identify primary factors inducing these rearfoot external eversion moments. Fourteen healthy men ran barefoot across a force plate embedded in the middle of 30-m runway with 3.30 ± 0.17 m · s–1. Total rearfoot external eversion/inversion moments (Mtot) were broken down into the component Mxy due to medio-lateral GRF (Fxy) and the component Mz due to vertical GRF (Fz). Ankle joint centre height and medio-lateral distance from the centre of pressure to the ankle joint centre (a_cop) were calculated as the moment arm of these moments. Mxy dominated Mtot just after heel contact, with the magnitude strongly dependent on Fxy, which was most likely caused by the medio-lateral foot velocity before heel contact. Mz then became the main generator of Mtot throughout the first half of the stance phase, during which a_cop was the critical factor influencing the magnitude. Medio-lateral foot velocity before heel contact and medio-lateral distance from the centre of pressure to the ankle joint centre throughout the first half of the stance phase were identified as primary factors inducing the rearfoot external eversion moment.