Football kick - biomechanics PDF

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A kinematic analysis of a dominant versus non-dominant side football kick. Introduction The kicking motion starts off with the approach of the ball with either one or more strides and the use of the other leg as support (Lees & Nolan, 1998). To start with the kicking leg is taken back by flexion at the knee, with the leg moving forward by the rotating of the pelvis around the standing leg (Lees & Nolan, 1998). As the leg moves forward the knee continues to flex (Lees & Nolan, 1998). As the thigh decelerates, the shank extends the knee to almost full extension (Lees & Nolan, 1998). The foot rotates in the medio-lateral and longitudinal axis (Lees & Nolan, 1998). It was found that a 30º angle created maximum velocity of the shank (Lees & Nolan, 1998). Wickstrom (1975) suggests that there are four stages to the kicking motion; the first stage is removing the thigh and shank whilst back swinging; the second stage is rotating the high and shank forwards (resulting in hip flexion); the third stage is where the thigh’s angular velocity reduces, resulting in an increase in shank angular velocity until impact on ball; the final stage is the follow through. Ball speed is a measure of kicking successfully (Lees & Nolan, 1998). Wallace and Norton (2014) used ball speed as a factor to show an improvement in football playing. Whilst playing football, it is crucial to have a faster ball speed, as it increases the chance of scoring. The faster the ball can travel will mean the less time the keeper would have to react (Dörge, Andersen, SØrensen & Simonsen, 2002). Furthering this, the most successful players are those who can score with both feet, so being able to get around the same ball velocity from both feet is important to improve as a footballer (Starosta, 1988). Hip rotation and hip flexion were found to be primary factors to ball velocity (Barfield, Kirkendall & Yu, 2002). Knowing this, it creates an area to experiment within. The loss of movement in soft tissues around a joint restricts the range of motion (ROM) creating an increased risk of injury (Harvey, Herbert & Crosbie, 2002). ROM is vital in football as it is known to help reduce and prevent injuries (Bradley & Portas, 2007). Bradley and Portas (2007) noted that footballers with less ROM in hip flexors and knee flexors were at a higher risk of strain injury. However, a player’s ROM may be less if they have recently been injured. Bradley and Portas (2007) found if a player had been injured in preseason their ROM was lower than expected. The aim of our experiment is to assess the difference in ROM and joint flexion between dominant and non-dominant legs whilst performing football kicks. After reviewing research.

The hypothesis was set as the dominant leg will have a larger ROM and joint flexion whilst performing a football kick. Method Sample 10 participants (6 males and 4 females) gave consent to participate in the experiment (mean ± SD age 19.9 years ± 1.6 years, height 1.7 metres ± 0.13 metres and mass 69.9 kg ± 7.9 kg). They were all healthy enough to participate, this was found by using self-reported health. The experiment provided a favourable ethical opinion. All participants were free from injury. Procedures The participant volunteered and their height (Stadiometer, Seca, Seca Ltd, UK) and mass (Scales, Seca, Seca Ltd, UK) were measured. A small cross of tape was placed on the floor for the participant to place the football. On the football, a small amount of reflective tape was stuck. This was to ensure that the cameras would be able to pick up the football. Six cameras were placed (Opus 300, Qualysis, Sweden) facing the cross placed on the floor. The computer then loaded the Qualysis system. The six cameras were then connected to the computer system. The cameras were then plugged into the wall with the power cable (120 w, Qualysis, Sweden). Using the computer system, the cameras were numbered from one – six, one being closest to the computer, and six furthest. The calibration item (Qualysis, Sweden) was placed on the floor. Using the calibration item, the cameras were adjusted so that they were all pointing towards it. Following this, the calibration wand (Qualysis, Sweden) was waved around the area that the participant would be stood in. The error was 1.06. Finally, the participant had five reflective markers (12 mm passive markers, spherical, flat base, Qualysis, Sweden) placed on; the glenohumeral joint (shoulder), greater trochanter (hip), lateral condyle (knee), lateral malleolus (ankle) and the 5th metatarsal phalangeal joint (toe), all in the sagittal plane. The participant then performed five kicks on his dominant foot, then five kicks on his non-dominant foot. The participant during the trails used the same kicking method, using their laces. This was recorded in the sagittal plane. Data Analysing The data was analysed using the Qualysis track manager (QTM) software. The successfully recorded videos were opened (started with non-dominant) and the markers were labelled on the body using the software. Throughout the video, some markers were missing, so QTM

creates predicted markers. By clicking on the markers, it enabled them to be filled, the software was able to predict where the marker should be from where it was last in shot, this is called interpolation. To calculate the joint ROM and joint angles, the three markers, that we were interested, in were highlighted and the button analyse was pressed. Placing the correct joints in the correct place allowed the main joint to be calculated. This created a graph, which was used to highlight the highest point and lowest point. For hip and knee, it was 180o minus the lowest angle. For ankle it was the highest value mins 90o. IBM SPSS Statistics 25 (USA, Chicago) was used to run a test of normality (Shapiro-Wilks). Finding the data for hip ROM, ankle ROM, hip flexion, ankle flexion and ball were not normally distributed, the non-parametric test (Wilcoxon Signed-Rank) was used. The date for knee ROM and knee flexion were parametric, so the paired sampled t test was used. The P value used was p ≥ 0.05. Wilcoxon Signed-Rank was chosen as the data was not parametric and was repeated measures. Effect size were calculated. For parametric data Cohen’s D was used. D= (mean of group 1 – mean of group 2)/ pooled SD. For non-parametric data, the r method was used. R=Z/√20. Cohen’s D is interpreted by: .2 = small effect, .6 = moderate effect, 1.2 = large effect, 2.0 = very large effect, 4.0 = extremely large effect. The r method is interpreted by: .1= small effect, .3= moderate effect, .5= large effect.

Results SPSS found most of the data to have significant difference. With the p value being p ≥ 0.05. For hip ROM (p=0.002), knee ROM (p=0.000), hip flexion (p=0.002), knee flexion (p=0.000), ankle flexion (p=0.004) and ball (p=0.002) all had significant differences found. Whereas, ankle ROM (p=0.695) was found to not be statistically significant. This means the alternative hypothesis is rejected and the null hypothesis must be accepted, there was not a significant difference. Most of the data was statistically significant, however, it was not all significant, so the alternative hypothesis must be rejected. Effect sizes for hip ROM (z=0.6), hip flexion (z=0.6), knee flexion (d=1.4) ankle flexion (z=0.6) and ball (z=0.6) all showed larger effects. Knee ROM (d=0.9) which is a moderate effect. Finally, ankle ROM (z=0.1) which is a small effect size.

Table 1: shows the means ± SD for the hip, knee and ankle flexion and ROM and ball velocity compared in dominant and non-dominant foot. Dominant

Non-dominant

Hip ROM (º)

94 ± 5

76 ± 13

Knee ROM (º)

86 ± 8

74 ± 5

Ankle ROM (º)

68 ± 7

72 ± 14

Hip Flexion (º)

106 ± 9

79 ± 14

Knee Flexion (º)

99 ± 6

89 ± 4

Ankle Flexion (º)

84 ± 7

80 ±

Ball velocity (m.s-1)

20.56 ± 1.78

12.73 ± 2.35

Discussion: The aim of this experiment was ‘to assess the difference in ROM and joint flexion between dominant and non-dominant legs in football kicks.’ After looking at previous evidence, the hypothesis was set as ‘The dominant leg will have a large ROM and joint flexion in football kicks.’ For the majority, this was correct, however, with the ankle the ROM was larger in the non-dominant foot. Hip ROM, knee ROM, hip flexion, Knee flexion, Ankle flexion and ball were all found to have a statistically significant difference. However, ankle ROM was not found to have a statistical difference, resulting in the rejecting of the alternative hypothesis. Furthering this, the effect sizes hip ROM, hip flexion, knee flexion, ankle flexion and the ball all show large effect sizes, meaning the results show these five factors do vary on the leg dominance. Whereas, knee ROM was moderate, showing a lower effect. Finally, ankle ROM had a small effect size which supports the data as there was no significant difference with ankle ROM. Dörge et al (2002) found an increase in ball speed with the dominant leg. This supports the data collected, with there being an increase in ball velocity in our data collected as well. Dörge et al. (2002) assumed the increase in ball speed was caused by a better inter-segmental motion pattern and a transfer of velocity from the foot to the football when kicking with the dominant leg. The dominant leg was found to produce a faster ball speed because it was able to gain more speed before kicking the ball (Dörge et al. 2002).

Bradley and Portas (2007) found that an increased ROM in the ankle resulted in overshooting. This supported our results, with the ankle ROM on the non-dominant foot being larger than the dominant. It may also suggest why the players decided to kick with their dominant foot as it provided better accuracy. This suggests that having a lower ankle ROM on both feet would be beneficial for the footballers. Bradley and Portas (2007) also found that knee ROM played an impact on height of the clearance. Taking this into consideration, prior to the trials, the participants position could have been recorded. Further research could be done comparing ROM in different positions. ROM can be used as a predictor of injury. Gomes, de Castro and Becker (2008) found that a decrease in hip ROM results in an increased risk of anterior cruciate ligament (ACL). This was found to be even more likely in football players compared to the general population (Gomes et al. 2008). The hip ROM was also decreased if the player had previously had an ACL injury (Gomes et al. 2008). Finding that 60% of athletes with ruptured ACL injuries have a decrease in hip ROM (Gomes et al. 2008). Knowing this, hip ROM could be monitored and if it decreases, it may be time for the physiotherapist to intervene to ensure that the ROM returns to its normal rate to reduce the risk of injury. Brophy et al. (2009) investigated the differences between male and female football players ROM in the lower extremity, finding that females had a larger ROM than males; although, males were stronger. Furthering that Brophy et al. (2009) looked into the increased risk of injury between males and females, finding that females are more likely to suffer from ACL injuries. All the players were at college level, so their may be a lack of generalisability to the population. Everyone in this study would be playing to a reasonable level, so it would be interesting to observe the differences between novice players and elite players. Zakas, Grammatikopoulou, Zakas, Zahariadis and Vamvakoudis (2006) compared joint flexion in the lower body between football players and volleyball players, looking to see if stretching and warm ups increased this. Finding a highly significant effect in hip flexion after passive stretching (Zakas et al. 2006). Zakas et al. (2006) did find that completing a warm up (jogging) only benefitted ankle flexion. Finding that the increase in muscle temperature paid no difference to joint flexibility, creating the need for passive stressing more vital for athletes who need to increase their joint flexibility (Zakas et al. 2006). Knowing this, coaches could ensure that they advise their athletes to partake in static stressing, by either incorporating it into their training or advising it outside of training.

It was found that a thirty second static stretch is as successful (if not more) in adolescent athletes as a five second stretch can be (Zakas, 2005). Zakas (2005) results showed no difference in ROM and joint flexion between different sides of the body, which contrasted the results that we collected. However, Zakas (2005) also found that both sides significantly increased their ROM and joint flexion after stretching occurred. It was also noted that similar results were found with children as well (Zakas, 2005). This idea would follow the known fact that the younger you are, the more flexible that you are. Creating a future research area, comparison of ages and joint flexibility and ROM within football players. The study did not occur without faults. The first noted limitation is that Qualysis had to do interpolation. This allowed the system to ‘fill in any gaps’ with the markers. To try counteracting this and keep it as accurate as possible, videos that had markers out of frame by the cameras for longer than three frames were discarded and rerecorded. However, it was impossible to get recordings with all markers in view of the cameras because of the action. Another noted limitation was the placement of the markers, these were placed on clothing. Resulting in them falling off and having to try to replace them back onto quickly. Clothing also can move, meaning that the marker may not have always been in the correct place. Finally, it was measured in a lab condition, meaning that the practical applications of the findings may not be as similar to a game situation. Conclusion It was found that there was an increase with joint ROM and joint flexion in all components, other than the ankle, in the dominant kicking leg compared to the non-dominant kicking leg. A statistical difference was found with hip ROM; knee ROM; hip flexion; knee flexion; ankle flexion and ball. Effect sizes for hip ROM, hip flexion, knee flexion, ankle flexion and the ball had a large effect size. Knee ROM had a moderate effect size and ankle ROM had a small effect size. Also comparing joint flexion and ROM over the ages of the footballers would be interesting. Further research could be done with females as more women are participating in football.

References: Barfield, W. R., Kirkendall, D. T., & Yu, B. (2002). Kinematic instep kicking differences between elite female and male soccer players. Journal of sports science & medicine, 1(3), 72. Bradley, P. S., & Portas, M. D. (2007). The relationship between preseason range of motion and muscle strain injury in elite soccer players. Journal of Strength and Conditioning Research, 21(4), 1155. Brophy, R. H., Chiaia, T. A., Maschi, R., Dodson, C. C., Oh, L. S., Lyman, S., ... & Williams, R. J. (2009). The core and hip in soccer athletes compared by gender. International journal of sports medicine, 30(09), 663-667. Dörge, H. C., Andersen, T. B., SØrensen, H., & Simonsen, E. B. (2002). Biomechanical differences in soccer kicking with the preferred and the non-preferred leg. Journal of sports sciences, 20(4), 293-299. Gomes, J. L. E., de Castro, J. V., & Becker, R. (2008). Decreased hip range of motion and noncontact injuries of the anterior cruciate ligament. Arthroscopy: The Journal of Arthroscopic & Related Surgery, 24(9), 1034-1037. Harvey, L., Herbert, R., & Crosbie, J. (2002). Does stretching induce lasting increases in joint ROM? A systematic review. Physiotherapy Research International, 7(1), 1-13. Lees, Adrian, and Lee Nolan. "The biomechanics of soccer: a review." Journal of sports sciences 16.3 (1998): 211-234. Starosta, W. (1988). Symmetry and asymmetry in shooting demonstrated by elite soccer players. Science and Soccer, 346ą355. Wallace, J. L., & Norton, K. I. (2014). Evolution of World Cup soccer final games 1966– 2010: Game structure, speed and play patterns. Journal of Science and Medicine in Sport, 17(2), 223-228. Wickstrom, R. L. (1975). Developmental kinesiology: Maturation of basic motor patterns. Exercise and sport sciences reviews, 3(1), 163-192. Zakas, A. (2005). The effect of stretching duration on the lower-extremity flexibility of adolescent soccer players. Journal of Bodywork and Movement Therapies, 9(3), 220-225.

Zakas, A., Grammatikopoulou, M. G., Zakas, N., Zahariadis, P., & Vamvakoudis, E. (2006). The effect of active warm-up and stretching on the flexibility of adolescent soccer players. Journal of sports medicine and physical fitness, 46(1), 57.

Football Kicking

Football kicking can be seen in five stage; the approach; the limb swing; foot-plant; hip and knee flexion and foot contact and, finally, the follow through. As shown in the photo, most of the action, of kicking, is using the lower body.

Qualitative assessment of football kick Below is one of the player’s data to be able to see the dominant versus the non-dominant leg. The athletes also had a decrease in ball velocity with the non-dominant leg. Dominant leg:

Non Dominant leg:

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The first notable difference is the shoulder position in the limb swing and contact with the ball. The shoulder is much further back, which may result in the ball landing above target.

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The second notable difference is the angle that the hip is at in ball contact. With nondominant leg, the hip, knee and shoulder are a straighter compared the dominant leg. Once again, showing the leaning away from the ball.

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The third notable difference is the increase if bending of the knee in the non-dominant leg, which may result in less power going through the ball.

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Finally, the dominant leg goes a lot higher through in the follow through than the nondominant leg. This may also result in the kicks being slightly off target.

Coaching recommendations 1. Improving the ROM (range of movement) would be reduce the risk of injury. Increasing the hip ROM would result in a reduce risk of an ACL injury. Following literature, the best way for that is static stretching. All stretches should be held for 30 seconds. Also, all stretches can be completed in the session or at home. The first suggested stretch is the hip flexor stretch. The athlete must slowly push the pelvis downwards while slightly arching their back until a stretch is felt. The second stretch is as shown. This stretches the knee, creating an increased ROM. The participant lays on their back; the knee is placed on their other leg. The third stretch is as shown. This stretches the ankle, increasing ROM. The athlete stands up and goes onto toes and then onto their heel. 2. An increase in strength training would benefit ball velocity as it would reduce any muscle imbalances. Focusing the movements on unilateral leg exercises The first suggested exercise is a single leg Romanian deadlift. This develops hip extension. Hold a dumbbell in one hand with and swing the same leg back as the hand the dumbbell is in. The second suggested exercise is a rear-foot elevated split squats. Place foot behind on a bench or box, holding the bar above their head they must bend their knee, performing a squat. Summary •

An increased ROM is beneficial for athletes to ensure a reduced risk of injury. However, if this is too large the athletes may be at risk as they are hypermobile.

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Increasing muscle power and strength in the non-dominant leg would result in an increase of ball velocity. Unilateral leg exercises have been suggested to make the non-dominant leg as strong as the dominant leg....