Age and gender differences in kinematics of powerful instep kicks in soccer.

Soccer kicking training should be adjusted to the characteristics of the athletes. Therefore, examination of differences in kicking kinematics of females and pubertal players relative to males is worthwhile. The purpose of the study was to compare kicking kinematics and segmental sequence parameters between male, female, and pubertal players. Ten adult male, ten adult female, and ten male pubertal players participated in the study. Participants performed five consecutive kicking trials of a stationary ball, as powerful as they could. Analysis of variance showed significantly higher ball velocity, higher joint linear velocities for the knee and the hip, and higher angular velocities of the knee and the ankle for males compared to female and pubertal players (p < 0.05). Similarly, the peak joint velocity was achieved significantly closer to ball impact in males compared to other groups (p < 0.05). Males also showed a more plantarflexed ankle immediately before ball impact (p < 0.05). Females and pubertal players may benefit from skill training aiming to increase ankle plantarflexion and hip flexion prior to ball impact, and to adjust thigh and shank motion, such that the shank-foot segment travels through a higher range of motion and with a greater velocity.

Metatarsophalangeal joint function during sprinting: a comparison of barefoot and sprint spike shod foot conditions.

The metatarsophalangeal joint is an important contributor to lower limb energetics during sprint running. This study compared the kinematics, kinetics and energetics of the metatarsophalangeal joint during sprinting barefoot and wearing standardized sprint spikes. The aim of this investigation was to determine whether standard sprinting footwear alters the natural motion and function of the metatarsophalangeal joint exhibited during barefoot sprint running. Eight trained sprinters performed maximal sprints along a runway, four sprints in each condition. Three-dimensional high-speed (1000 Hz) kinematic and kinetic data were collected at the 20 m point. Joint angle, angular velocity, moment, power and energy were calculated for the metatarsophalangeal joint. Sprint spikes significantly increase sprinting velocity (0.3 m/s average increase), yet limit the range of motion about the metatarsophalangeal joint (17.9% average reduction) and reduce peak dorsiflexion velocity (25.5% average reduction), thus exhibiting a controlling affect over the natural behavior of the foot. However, sprint spikes improve metatarsophalangeal joint kinetics by significantly increasing the peak metatarsophalangeal joint moment (15% average increase) and total energy generated during the important push-off phase (0.5 J to 1.4 J). The results demonstrate substantial changes in metatarsophalangeal function and potential improvements in performance-related parameters due to footwear.

Recovery of powerful kick biomechanics after intense running fatigue in male and female soccer players.

BACKGROUND: Fatigue seems to have a significant effect on soccer kick performance. However, the duration of these effects has not been previously investigated. OBJECTIVES: The purpose of the present study was to investigate the duration of the acute effects of fatigue on soccer kick performance in males and females. PATIENTS AND METHODS: Ten male (age: 26.3 ± 4.9 years, height: 178.1 ± 5.1 cm, mass: 81.3 ± 8.1 kg) and ten female (age: 24.4 ± 4.2 years, height: 169.7 ± 5.7 cm, mass: 61.8 ± 5.1 kg) amateur soccer players performed three instep kicks prior to and after running on a treadmill till exhaustion. Three-dimensional kinematics were collected pre- and post-fatigue. RESULTS: Analysis of variance indicated a statistically significant decline in ball speed during the first and the second trial after fatigue (P < 0.05), but recovered to pre-fatigue levels during the third post-fatigue kicking trial (P > 0.05). Similarly, maximum ankle, knee and hip linear velocity and ankle angular displacement were significantly lower during the first two trials (P < 0.05), but not during the third trial after fatigue (P > 0.05). CONCLUSIONS: Soccer kick parameters recovered to pre-fatigue levels approximately within a minute after the end of the protocol. These findings have a practical meaning for players who have to perform set piece kicks under fatigue conditions and for coaches who have to guide their players.

Variability and typical error in the kinematics and kinetics of the maximal instep kick in soccer.

The purpose of this paper was to establish the variability and typical error of kinematic and kinetic variables representing the maximal instep kick in soccer for both the kicking and support legs. Ten skilled (good amateur or semi-professional) soccer players performed 20 maximal instep kicks of a stationary ball into a goal mouth. Motion of the kicking and support legs was recorded by an optoelectronic motion analysis system, and a six degrees of freedom model was used to compute kinematic and kinetic variables. Participants repeated the kicks on a second day at least 1 week later. The mean within-subject coefficient of variation across the kinematic and kinetic variables, trials, and days was 16% and did not change substantially as trial number increased or between day of test. Increasing trial number reduced the typical error (as determined by the standard error of the mean) such that for 20 trials 75% of the variables were below an arbitrary 5% threshold. It was concluded that for kicking investigations, 10-15 trials could be used and typical errors of 5% should be expected.

Mechanisms that influence accuracy of the soccer kick.

Goal scoring represents the ultimate purpose of soccer and this is achieved when players perform accurate kicks. The purpose of the present study was to compare accurate and inaccurate soccer kicks aiming to top and bottom targets. Twenty-one soccer players performed consecutive kicks against top and bottom targets (0.5m(2)) placed in the center of the goal. The kicking trials were categorized as accurate or inaccurate. The activation of tibialis anterior (TA), rectus femoris (RF), biceps femoris (BF) and gastrocnemius muscle (GAS) of the swinging leg and the ground reaction forces (GRFs) of the support leg were analyzed. The GRFs did not differ between kicking conditions (P > 0.05). There was significantly higher TA and BF and lower GAS EMG activity during accurate kicks to the top target (P < 0.05) compared with inaccurate kicks. Furthermore, there was a significantly lower TA and RF activation during accurate kicks against the bottom target (P < 0.05) compared with inaccurate kicks. Enhancing muscle activation of the TA and BF and reducing GAS activation may assist players to kick accurately against top targets. In contrast, players who display higher TA and RF activation may be less accurate against a bottom target. It was concluded that muscle activation of the kicking leg represents a significant mechanism which largely contributes to soccer kick accuracy.

Measurement procedures affect the interpretation of metatarsophalangeal joint function during accelerated sprinting.

The metatarsophalangeal joint (MPJ) is a significant absorber of energy in sprinting. This study examined the influence of MPJ axis choice and filter cut-off frequency on kinetic variables describing MPJ function during accelerated sprinting. Eight trained sprinters performed maximal sprints along a runway. Three-dimensional high-speed (1000 Hz) kinematic and kinetic data were collected at the 20 m point. Three axis definitions for the five MPJs were compared. MPJ moments, powers and energies were calculated using different filter cut-off frequencies. The more anatomically appropriate dual axis resulted in less energy absorbed at the MPJ compared to the oblique axis which also absorbed less energy compared to the perpendicular axis. Furthermore, a low cut-off frequency (8 Hz) substantially underestimated MPJ kinematics, kinetics and the energy absorbed at the joint and lowered the estimate of energy production during push-off. It is concluded that a better understanding of MPJ function during sprinting would be obtained by using an oblique or anatomically appropriate representation of the joint together with appropriate kinematic data sampling and filtering so that high frequency movement characteristics are retained.

Early visual cues associated with a directional place kick in soccer.

The purpose of this paper was to establish postural cues in kicking that may be of use to goalkeepers. Eight male soccer players (age 20.5 +/- 1.1 yrs; height 1.78 +/- 0.053 m; mass 75.18 +/- 9.66 kg) performed three types of kick: a low side-foot kick to the left hand corner of the goal, a low side-foot kick straight ahead, and a low instep kick straight ahead. Kicks were recorded by an optoelectronic motion analysis system at 240 Hz. At kicking foot take-off (about 200 ms before ball contact) the variables which were significantly different and could act as cues were support foot progression angle, pelvis rotation, and kicking hip and ankle flexion. The support foot progression angle was considered to be the most valuable of these variables as its angle coincided with the direction of ball projection. The other variables were less clear in their interpretation and so less valuable for a goalkeeper to use for decision making. Cues appearing after support foot contact were thought unlikely to be of value to a goalkeeper in their decision making. These include kicking leg knee flexion angle, and support leg shank and thigh angles.

Single maximal versus combination punch kinematics.

The aim of this study was to determine the influence of punch type (Jab, Cross, Lead Hook and Reverse Hook) and punch modality (Single maximal, 'In-synch' and 'Out of synch' combination) on punch speed and delivery time. Ten competition-standard volunteers performed punches with markers placed on their anatomical landmarks for 3D motion capture with an eight-camera optoelectronic system. Speed and duration between key moments were computed. There were significant differences in contact speed between punch types (F(2,18,84.87) = 105.76, p = 0.001) with Lead and Reverse Hooks developing greater speed than Jab and Cross. There were significant differences in contact speed between punch modalities (F(2,64,102.87) = 23.52, p = 0.001) with the Single maximal (M+/- SD: 9.26 +/- 2.09 m/s) higher than 'Out of synch' (7.49 +/- 2.32 m/s), 'In-synch' left (8.01 +/- 2.35 m/s) or right lead (7.97 +/- 2.53 m/s). Delivery times were significantly lower for Jab and Cross than Hook. Times were significantly lower 'In-synch' than a Single maximal or 'Out of synch' combination mode. It is concluded that a defender may have more evasion-time than previously reported. This research could be of use to performers and coaches when considering training preparations.

Solutions for representing the whole-body centre of mass in side cutting manoeuvres based on data that is typically available for lower limb kinematics.

While studying detailed lower limb mechanics of dynamic sports manoeuvres like side cutting it is often desirable but practically difficult to directly measure velocity profiles of the whole-body centre of mass (CoM). In the current study, representations of CoM, either based on a single marker placed on the pelvis or thorax, or based on segment kinematics of lower limbs with or without inclusion of trunk, were evaluated against whole-body CoM representation. Using the 95% limits of agreement method for comparison of two methods, strongest agreement was found between velocity of whole-body CoM and CoM representation based on lower limbs with the addition of the trunk. The CoM representation based on lower limbs only showed weaker agreement, but this representation was still markedly superior to single marker representations.

The influence of Cardan rotation sequence on angular orientation data for the lower limb in the soccer kick.

The influence of the Cardan rotation sequence on the orientation angles for joints is well known but has not been explored for dynamic sports movements. The purpose of this study is to establish the influence of Cardan rotation sequence on the orientation angles of the ankle, knee, and hip of the support leg and pelvis during dynamic sports movements, typified by a maximal instep kick in soccer. We found that: (a) the X (flexion/extension) axis rotations provide data that are robust for any sequence used other than the YXZ sequence, although the Y (abduction/adduction) and Z (internal/external) axes rotations are variable in both shape and offset magnitude; (b) the preferred rotation sequence is either XYZ or XZY for dynamic sports movements, although for the soccer kick the XYZ rotation sequence has been widely used and so this is recommended as a standard; and (c) most uncertainties exist in the Y and Z axes and are most apparent at the beginning of the movement. Where uncertainty exists in identifying Y and Z axes orientations, the integrated angular velocity may be considered as an alternative to determine the relative changes in segment orientation.

Effect of a 9-wk. after-school multiskills club on fundamental movement skill proficiency in 8- to 9-yr.-old children: an exploratory trial.

This exploratory study examined the effects of a 9-wk. after-school multiskills club on fundamental movement skill proficiency in 8- to 9-yr.-old children. Two schools were randomly assigned to either a control (n = 15 children) or multiskill club (n = 19 children) condition. The multiskill club received 18 coaching sessions designed to improve fundamental movement skills. The control group followed normal routines. 7 skills were assessed using process-oriented measures with video analysis. Participation in the multiskill club yielded significant improvements in proficiency at posttest only in static balance, while potentially practically important improvements were observed in performance of the catch, throw, and kick skills. The after-school multiskill club offered a viable opportunity for movement skill acquisition, but any such programme would need to run for a longer duration to assess whether this type of activity could benefit all skills.

Effect of forward trunk inclination on joint power output in vertical jumping.

It is commonly accepted that vertical jump performance is a good indicator of maximal joint power. Some studies, however, have indicated that knee joint power output in the vertical jump is limited due to forward trunk inclination early in the push-off. The aim of this experimental study was to investigate the effect of forward trunk inclination on joint power output in vertical jumping. A group of 20 male subjects performed maximal vertical countermovement jumps from stance while minimizing the contribution of arm swing by holding their hands on their hips (arms akimbo). They also performed maximal jumps while holding the trunk as upright as possible throughout the jump, still holding the arms akimbo. Jump height, joint kinematics (angles), and joint kinetics (torque, power) were calculated. Jump height of vertical jumps while holding the trunk upright was 10% less than in normal jumps. Hip joint power was decreased by 37% while knee joint power was increased by 13%. Ankle joint power did not change. These results demonstrated that maximal jump performance does not necessarily represent maximal power of each individual joint. The implication is that jump performance may well be a good representation of overall joint power; it is, however, not an accurate measure to evaluate maximal individual joint power as part of contemporary training and rehabilitation methods.

The influence of lower limb amputation level on the approach in the amputee long jump.

In this study, we investigated the adjustments to posture, kinematic and temporal characteristics of performance made by lower limb amputees during the last few strides in preparation for long jump take-off. Six male unilateral trans-femoral and seven male unilateral trans-tibial amputees competing in a World Championships final were filmed in the sagittal plane using a 100-Hz digital video camera positioned so that the last three strides to take-off were visible. After digitizing using a nine-segment model, a range of kinematic variables were computed to define technique characteristics. Both the trans-femoral and trans-tibial athletes appeared to achieve their reduction in centre of mass during the flight phase between strides, and did so mainly by extending the flight time by increasing stride length, achieved by a greater flexion of the hip joint of the touch-down leg. The trans-tibial athletes appeared to adopt a technique similar to that previously reported for able-bodied athletes. They lowered their centre of mass most on their second last stride (-1.6% of body height compared with -1.4% on the last stride) and used a flexed knee at take-off on the last stride, but they were less able to control their downward velocity at touch-down (-0.4 m x s(-1)). Both this and their restricted approach speed (8.9 m x s(-1) at touch-down), rather than technique limitations, influenced their jump performance. The trans-femoral athletes lowered their centre of mass most on the last stride (-2.3% of body height compared with -1.6% on the second last stride) and, as they were unable to flex their prosthetic knee sufficiently, achieved this by abducting their prosthetic leg during the support phase, which led to a large downward velocity at touch-down (-0.6 m x s(-1)). This, combined with their slower approach velocity (7.1 m x s(-1) at touch-down), restricted their performance.

Kinematic response characteristics of the CAREN moving platform system for use in posture and balance research.

The CAREN system is a new and unique device for use in postural and balance research in clinical settings due to its ability to independently perturb the support surface in each of six degrees of freedom. Users of this system need knowledge of its technical performance which is not available. The aim of this study was to determine the technical performance of the CAREN system by defining its kinematic response characteristics to two commonly used input functions (sine and ramp) for each of its six translational and rotational axes. The translational and rotational displacement, velocity and acceleration limits of the CAREN system suggest that it is a mid-range system with regard to single degree of freedom moving platform devices reported in the literature. The maximum average displacement cross-talk was 1.5% of the viable working range in any specified direction. The maximum average velocity cross-talk was 3.3% of its maximum velocity in any specified direction. The CAREN system was able to respond to ramp input functions within its displacement and velocity limits although, for short duration ramps, there was evidence that target velocity was not reached. It is concluded that the CAREN system is an appropriate device for postural and balance research with some unique features. This specification of its technical performance should help researchers to identify the tasks for which it is most suitable.

Gait quality assessment using self-organising artificial neural networks.

In this study, the challenge to maximise the potential of gait analysis by employing advanced methods was addressed by using self-organising neural networks to quantify the deviation of patients' gait from normal. Data including three-dimensional joint angles, moments and powers of the two lower limbs and the pelvis were used to train Kohonen artificial neural networks to learn an abstract definition of normal gait. Subsequently, data from patients with gait problems were presented to the network which quantified the quality of gait in the form of a single curve by calculating the quantisation error during the gait cycle. A sensitivity analysis involving the manipulation of gait variables' weighting was able to highlight specific causes of the deviation including the anatomical location and the timing of wrong gait patterns. Use of the quantisation error can be regarded as an extension of previously described gait indices because it measures the goodness of gait and additionally provides information related to the causes underlying gait deviations.

A method for manipulating a movable platform's axes of rotation: a novel use of the CAREN system.

The functionality of movable platforms used in human balance studies is limited as they allow rotations around pre-defined axes, which typically run close to the platform's surface and so cannot be used to directly investigate control mechanisms of proximal joints. A new six degrees of freedom platform (CAREN, Motek, Amsterdam) is now available which in principle could be programmed to rotate around any axis of rotation. The location of the default axes of rotation for this device are not documented and the algorithm to move the axes has not yet been defined. The purpose of this study was to (1) locate the platform's default axes of rotation, (2) implement an algorithm for relocating its axes of rotation and (3) evaluate the algorithm. A simplified method was developed to locate the bounding rectangles within which the default axes of rotations were located. The three axes of rotation were found to be at x=1.13+/-0.69 mm, z=-204.22+/-0.63 mm in the roll plane, y=-2.67+/-0.59 mm, z=-211.38+/-0.63 mm in the pitch plane and x=0.43+/-0.70 mm, y=-4.72+/-0.65 mm in the yaw plane (X: left, Y: rear, Z: up), relative to the centre of its surface, with the maximum bounding rectangle of dimensions 2.50mm by 2.42 mm. Relocation of the platform's axes of rotation was achieved by the use of compensatory corrections, which were determined using a translation algorithm. Evaluation of the algorithm involved pitching the platform around three newly defined axes in the sagittal plane, representing the ankle, knee and hip joints. The platform was able to rotate around the new axes while keeping the instantaneous axes of rotation within bounding rectangles of 1.87 mm x 0.81 mm (ankle), 3.04 mm x 1.23 mm (knee), 3.14 mm x 1.63 mm (hip). The ability to overcome the limitation of other moveable platforms makes the CAREN system a valuable tool in research on the role of individual joints in balance.

Visualisation of gait data with Kohonen self-organising neural maps.

Self-organising artificial neural networks were used to reduce the complexity of joint kinematic and kinetic data, which form part of a typical instrumented gait assessment. Three-dimensional joint angles, moments and powers during the gait cycle were projected from the multi-dimensional data space onto a topological neural map, which thereby identified gait stem-patterns. Patients were positioned on the map in relation to each other and this enabled them to be compared from their gait patterns. The visualisation of large amounts of complex data in a two-dimensional map labelled with gait patterns is a step towards more objective analysis protocols which may enhance decision making.

Electromyography of selected lower-limb muscles fatigued by exercise at the intensity of soccer match-play.

Surface electromyography has been useful in comparing muscular activity among different sports movements and it is a valuable technique for evaluating muscle activation, co-ordination and fatigue. Since these important variables have not been investigated during the full game in soccer, the present study aimed to investigate the activity of major muscles of the lower extremity during a soccer-simulation fatiguing protocol. Ten amateur soccer players (age 21.40+/-3.13 years; height 1.77+/-0.06 m; mass 74.55+/-8.5 kg) were tested. The exercise protocol, performed on a programmable motorised treadmill, consisted of the different intensities observed during soccer match-play (walking, jogging, running, sprinting). Electromyographic activity was recorded from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius (GC) muscles before exercise, at half-time and immediately after the 90-min exercise protocol. The EMG data were analysed using custom-written software to compute the root mean square (RMS) value over ten gait cycles. With regard to RF, BF and TA, a significant main effect (P< 0.05) was found for condition (pre-game, half-time and post-game), speed (6, 12, 15 and 21 km h(-1)) (P<0.05) and interaction between condition and speed (P< 0.05). For GC, a significant effect was not found for condition or interaction between condition and speed, but a significant main effect (P< 0.001) was found for speed, with the RMS value increasing continually with increasing speed from 6 to 2 1km h(-1). The results indicated that after a simulation of the exercise intensity of soccer-play the EMG activity in major lower-limb muscles was less than before. This decrease indicated that prolonged intermittent exercise had an effect on muscle activity even when work-rate was sustained.

The energetics and benefit of an arm swing in submaximal and maximal vertical jump performance.

The aims of this study were to investigate the energy build-up and dissipation mechanisms associated with using an arm swing in submaximal and maximal vertical jumping and to establish the energy benefit of this arm swing. Twenty adult males were asked to perform a series of submaximal and maximal vertical jumps while using an arm swing. Force, motion and electromyographic data were recorded during each performance and used to compute a range of kinematic and kinetic variables, including ankle, knee, hip, shoulder and elbow joint powers and work done. It was found that the energy benefit of using an arm swing appears to be closely related to the maximum kinetic energy of the arms during their downswing, and increases as jump height increases. As jump height increases, energy in the arms is built up by a greater range of motion at the shoulder and greater effort of the shoulder and elbow muscles but, as jump height approaches maximum, these sources are supplemented by energy supplied by the trunk due to its earlier extension in the movement. The kinetic energy developed by the arms is used to increase their potential energy at take-off but also to store and return energy from the lower limbs and to "pull" on the rest of the body. These latter two mechanisms become more important as jump height increases with the pull being the more important of the two. We conclude that an arm swing contributes to jump performance in submaximal as well as maximal jumping but the energy generation and dissipation sources change as performance approaches maximum.

Comparison of muscle strength and flexibility between the preferred and non-preferred leg in English soccer players.

Most soccer players have a favoured foot for kicking the ball, and it is believed that this preference may lead to an asymmetry in the strength and flexibility of the lower extremities. This study was designed to determine whether asymmetry in strength and flexibility are present in the legs of soccer players.Forty-one elite and sub-elite soccer players (age 23.4 +/- 3.8 years; height 1.81 +/- 0.06 m; body mass 81.7 +/- 9.9 kg) were studied (data are presented as mean +/- SD). The dynamic strength of knee flexors (hamstrings) and knee extensors (quadriceps) was measured using an isokinetic dynamometer at angular velocities of 1.05, 2.09, 5.23 rad/s (in a concentric mode) and 2.09 rad/s (in an eccentric mode). The concentric strength ratio (hamstrings(conc)/quadriceps(conc)) and the dynamic control ratio (hamstrings(ecc)/quadriceps(conc)) were computed. Hip joint flexibility (in flexion) was measured using a goniometer.A significant difference between the preferred and non-preferred leg was found in the knee flexors at 2.09 rad/s (119 +/- 22 versus 126 +/- 24 Nm; P < 0.05) and for the dynamic control ratio (0.79 +/- 0.13 versus 0.84 +/- 0.16 Nm; P < 0.05). In both cases the knee flexors of the preferred leg were weaker than those of the non-preferred leg. A total of 28 of the 41 players (68%) had significant musculoskeletal abnormality (imbalance >10%) in one or more specific muscle groups. No significant differences were found in flexibility of the hip joint between the preferred and non-preferred leg (P > 0.05). It is concluded that the lower strength of the knee flexor muscles of the preferred leg may be associated with the differential use of these muscle during the kicking action and thus constitutes a unique training effect associated with soccer. This in turn can lead to muscular imbalance which is generally regarded as an injury risk factor.