Documentation:FIB book/Heading in Soccer

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Background

The biomechanics of (sub)concussive head impacts is not well understood. Therefore, the long-term effect of repeated head impacts, such as heading in soccer, causes concern. Ling et al (2017)[1] found a potential link between repetitive head impacts from playing soccer and the neurodegenerative brain disease, chronic traumatic encephalopathy, as the cause of dementia in several retired professional soccer players. Brain injury expert Dr Bennet Omalu calls to restrict heading in the professional game and ban for those under the age of 18, since the brain is still developing.[2] In the past years, the Belgian youth competition has banned throw ins, as the ball was often intercepted using the head, and the US has even banned heading in youth soccer altogether. However, many countries have not yet adopted this safer approach to heading in youth competitions. A definitive link between repetitive heading in soccer and negative long-term cognitive effects has yet to be established.

The exact process of concussion is not completely understood. There are many vague definitions of concussion, usually involving some kind of external insult that leads to symptoms, such as dizziness, confusion, nausea, temporary loss of consciousness and headaches.[3] One working definition of concussion (also referred to as mild traumatic brain injury or mTBI) is a clinical syndrome with neurological-cognitive-behavioural signs and symptoms caused by acceleration, deceleration or rotational forces on the head. (Kamins and Giza, 2016)[4]. Subconcussion is a subclinical injury that is caused by biomechanical forces but is presented without acute signs and symptoms (Kamins and Giza, 2016)[4]. So in subconcussive events there might be structural damage or physiological changes in the brain, but it does not cause observable functional problems. The effects of repetitive subconcussive head trauma on long term brain function, however, has revealed contradictory findings in literature. Lipton et al. (2013)[5] conducted a study investigating the relationship between subclinical evidence of TBI and soccer heading. It was found that although no participants had a history of concussion, repeated heading was linked to a long term decrease in cognitive performance and higher risk of microstructural white matter changes in the brain. Jones et al (2014)[6] executed a study assessing the relationship between low level head trauma due to heading and long-term cognitive decline. No evidence was found linking accelerated cognitive decline and chronic sub-concussive head injury. It was further concluded that short and medium term cognitive decline may be transient, with the players’ brain function mirroring that of the standard population once they retire from the sport.

In this section we will give an overview of research that has attempted to quantify the accelerations that are experienced by soccer players when heading a ball. We will also look into research that has quantified a limit for the forces and accelerations causing concussion.

Measuring the Impacts

Several studies have been done to quantify the magnitude of forces and acceleration acting on the head during heading in soccer. This can be related to calculated head injury criteria (HIC) and to other studies that establish limits for mild traumatic brain injury.

An example of a study that evaluated accelerations in heading impacts is by Funk et al (2011)[7]. They evaluated the mean peak values of linear acceleration and rotational acceleration caused by a soccer ball impact to the forehead. The ball was released and struck the subjects’ forehead, who did not attempt to actively head the ball. They tested at several different impact velocities (5, 8.5, 10 and 11.5 m/s). The average peak linear acceleration corresponding to the different ball velocities ranged from 6.8- 21 g and the average peak rotational acceleration ranged from 361-2217 rad/s2.

However, such static impacts in a laboratory setting might not give an accurate impression of the head impacts that occur while actively playing soccer. Therefore, different studies have been done to assess heading impacts in real life situations. For instance, Miller et al (2019)[8] assessed head impact exposure during games and practice in youth female soccer players by measuring head kinematics using instrumented mouthpieces. Video analysis was used to describe the source of each head impact. The results showed that the average peak linear and rotational acceleration values from impacts during games were 14.6 g and 1,305 rad/s2. Table 1 gives an overview of several studies that directly correlate heading in soccer with accelerations of the head. It can be seen that in none of the studies concussions were sustained when heading a ball. However, some participants experienced symptoms such as slight ringing in the ear, headaches or being momentarily dazed.

Table 1: Peak linear acceleration and peak rotational acceleration measured in soccer headers.

Study Peak linear acceleration (g) Peak rotational acceleration (rad/s2) Measurement method Situation Concussion sustained Symptoms reported
Funk et. al. (2011)[7] 6.8 - 21 361- 2217 Tri-axial accelerometers in mouthpiece Soccer balls shot at forehead at velocities 5, 8.5, 10 and 11.5 m/s, no active heading No Slight ringing in the ear, momentarily dazed, headaches, neck tightness
Naunheim et. al. (2003)[9] 20.29 1302 Three triaxial accelerometers mounted to the head Mechanical soccer ball driver projected balls at subjects in a laboratory No NR
Miller et. al. (2019)[8] 14.6 1305 Tri-axial accelerometers and gyroscope in mouthpiece, video analysis Head impacts occurring during soccer games and practice No NR
Harriss et. al. (2019)[10] 27.35 1447.42 Tri-axial accelerometers and tri-axial gyroscope in headband Head impacts during regular soccer games No NR

Table 1 shows a significant range of values for accelerations experienced when heading a soccer ball, with peak linear acceleration ranging from 6.8 to 27.35 g and peak rotational acceleration ranging from 361 to 2217 rad/s2.

Defining the Limit

The values of head accelerations are meaningless if they cannot be compared to values that correspond to mTBI. Various studies have been compiled which take a look at mTBI thresholds for linear and angular accelerations in men’s football, men’s hockey, women’s hockey, highschool football, and college football. Two animal studies have also been included to see if there is a trend between the acceleration experienced by the brain. These values hold significance as although the measurements are from differing sports, they can help us quantify an overarching limit for mTBI. Namjoshi et al. (2017)[11] attempted to define the lower limit of mTBI using a closed impact model of engineered rotational acceleration (CHIMERA). In the experiment mice received impacts to the head at different energies, corresponding to sub-threshold, threshold and mild TBI values. The results were scaled to human values. The corresponding equivalent human head kinematics values at threshold energy were a peak linear acceleration of 38 g and a peak angular acceleration of 782 rad/s2. Many other studies have related the actual occurrence of concussive events to the head accelerations that occurred during the impact that caused the concussion. Table 2 provides an overview of several studies that describe threshold values for linear and rotational acceleration that cause concussion.

Table 2: Classification of Concussion Threshold for linear acceleration and rotational acceleration values in sports.

Study Threshold value peak linear acceleration (g) Threshold value peak rotational acceleration (rad/s2) Measurement method Situation
O'Connor et. al. (2017)[12] 69.7 to 145

30.7 to 31.7

30.4 to 52.2

7688

5419

4030

Helmet Accelerometer

Helmet Accelerometer

Helmet Accelerometer

Football

Men's Hockey

Women’s Hockey

Namjoshi et. al. (2017)[11] 38 782 CHIMERA animal model for closed head impacts Mice received impacts to the head at different energies, corresponding to sub-threshold, threshold and mild TBI values.
Rowson et. al. (2013)[13] 104 4726 Instrumented helmets Men’s football
Broglio et. al. (2010)[14] 96.1 5582 Head Impact Telemetry System High school football
Greenwald et. al. (2008)[15] 96 7235 Six single-axis accelerometers embedded in helmets High school football
Funk et. al. (2007)[16] 165 9000 Head-mounted accelerometers College football
Frechede et. al. (2009)[17] 103 8022 MADYMO simulation Reconstructed video analysis of football and rugby players
Ommaya et. al. (1967)[18] NR 7500 Derived from displacement data Primates were subjected to a range of angular accelerations

Evidently, significant discrepancies arise when assessing the linear and angular acceleration magnitudes required to induce a concussion, with threshold values ranging from 30.4-165g and 782-9000 rad/s2 for linear and angular acceleration respectively. The values for the threshold of linear and angular acceleration from table 2 are visually represented in figures 1 and 2. Each colour represents the value found in a particular sport scenario. Each bar represents a different study.

Figure 1: Mean Peak Linear Accelerations for mTBI in Various Situations

Mean Peak Linear Accelerations for mTBI in Various Situations.jpg

Figure 2: Mean Peak Angular Accelerations for mTBI in Various Situations

Mean Peak Angular Accelerations for mTBI in Various Situations.jpg

Limitations of the Research

As stated previously, mTBI occurs when the brain is displaced within the skull. It can be seen in table 1 that there is variation between studies for the obtained values of accelerations in heading. It is important to note that these differences can be caused by variations in the set up (such as ball speed, weight of the ball, variability between participants etc) but also by different measurement methods. Since the sensors are not rigidly coupled to the skull there can be relative motion between the sensors and the skull, which reduces the accuracy of the data and leads to different values between different sensors[19]. Another limitation of the body of research is that papers that quantify accelerations in soccer headings are primarily focused on young female athletes, which is not very representative for the entire soccer playing population. The accuracy of the sensors is a limitation in both the studies quantifying accelerations in heading and the studies that quantify a limit for mTBI. A limitation of the animal studies that quantified an mTBI threshold is that mice and primates obviously differ in anatomy from humans. Therefore, an estimation had to be made to scale the resulting accelerations to accelerations that would cause mTBI in humans. Also, one study used MADYMO simulations, which were validated through crash-sled simulation testing. It is unclear if these simulations are useful for sports impacts because it has been validated for a vastly different scenario. Additionally, controlled studies are restricted as giving individuals concussions to obtain data is not ethically correct.

Conclusion

Evidently, the values of accelerations in soccer heading presented in Table 1 fall well below the documented threshold values for concussion seen in Table 2. Thus, it can be concluded that a singular head impact with the ball is not likely to cause concussion. However, some headers were enough to cause symptoms such as headaches, suggesting the incidence of subconcussive head trauma. The effects of repetitive subconcussive head trauma on long term brain function reveal conflicting findings, allowing no concrete conclusion to be drawn. Thus, in consideration of the developing brain in individuals under eighteen, it is strongly recommended to implement a complete ban of heading the ball. Rather than banning heading all together in adults games, further research is required to gain an understanding of the effects of repeated subconcussive impacts on brain injury. The establishment of safety guidelines in adults soccer to minimize these risks is highly recommended.

Further research on mTBI needs to be done in order for it to be accurately classified and diagnosed. The main concern is the accuracy of the data. Sensors that can measure the accelerations of the brain and not the skull need to be developed to increase the accuracy of data acquisition. More data needs to be obtained from a diversified pool of soccer players as most of the data obtained for soccer is from young girls. Also, longitudinal studies must be done to evaluate the long term effect of repetitive subconcussive events.

References

  1. Ling, H., Morris, H.R., Neal, J.W., Lees, A.J., Hardy, J., Holton, J.L., Revesz, T., Williams, D.D.R, 2017. Mixed pathologies including chronic traumatic encephalopathy account for dementia in retired association football (soccer) players, Acta Neuropathologica, 133-3, 337-352
  2. "Brain injury expert calls for ban on heading in football". BBC. 8 August 2018.
  3. Polinder, S., Cnossen, M. C., Real, R., Covic, A., Gorbunova, A., Voormolen, D. C., von Steinbuechel, N. (2018). A Multidimensional Approach to Post-concussion Symptoms in Mild Traumatic Brain Injury. Frontiers in neurology, 9, 1113.
  4. 4.0 4.1 Kamins, J., Giza, C.C., 2016. Concussion—Mild Traumatic Brain Injury: Recoverable Injury with Potential for Serious Sequelae, Neurosurgery Clinics of North America, 27-4, 441-452
  5. Lipton, M.L., Kim, N., Zimmerman, M.E., Kim, M., Stewart, W.F., Branch, C.A. and Lipton, R.B., 2013. Soccer heading is associated with white matter microstructural and cognitive abnormalities. Radiology, 268(3), pp.850-857.
  6. Jones, S.A.V., Breakey, R.W. and Evans, P.J., 2014. Heading in football, long-term cognitive decline and dementia: evidence from screening retired professional footballers. Br J Sports Med, 48(2), pp.159-161
  7. 7.0 7.1 Funk, J.R., Cormier, J.M., Bain, C.E., Guzman, H., Bonugli, E. and Manoogian, S.J., 2011. Head and neck loading in everyday and vigorous activities. Annals of biomedical engineering, 39(2), pp.766-776
  8. 8.0 8.1 Miller, L.E., Pinkerton, E.K., Fabian, K.C., Wu, L.C., Espeland, M.A., Lamond, L.C., Miles, C.M., Camarillo, D.B., Stitzel, J.D. and Urban, J.E., 2019. Characterizing head impact exposure in youth female soccer with a custom-instrumented mouthpiece. Research in Sports Medicine, pp.1-17.
  9. Naunheim, R.S., Standeven, J., Richter, C. and Lewis, L.M., 2003. Comparison of impact data in hockey, football, and soccer. Journal of Trauma and Acute Care Surgery, 48(5), pp.938-941.
  10. Harriss, A., Johnson, A.M., Walton, D.M. and Dickey, J.P., 2019. Head impact magnitudes that occur from purposeful soccer heading depend on the game scenario and head impact location. Musculoskeletal science and practice, 40, pp.53-57.
  11. 11.0 11.1 Namjoshi, D.R., Cheng, W.H., Bashir, A., Wilkinson, A., Stukas, S., Martens, K.M., Whyte, T., Abebe, Z.A., McInnes, K.A., Cripton, P.A. and Wellington, C.L., 2017. Defining the biomechanical and biological threshold of murine mild traumatic brain injury using CHIMERA (Closed Head Impact Model of Engineered Rotational Acceleration). Experimental neurology, 292, pp.80-91
  12. O'Connor, K.L., Rowson, S., Duma, S.M. and Broglio, S.P., 2017. Head-impact–measurement devices: a systematic review. Journal of athletic training, 52(3), pp.206-227
  13. Rowson, S. and Duma, S.M., 2013. Brain injury prediction: assessing the combined probability of concussion using linear and rotational head acceleration. Annals of biomedical engineering, 41(5), pp.873-882
  14. Broglio, S.P., Schnebel, B., Sosnoff, J.J., Shin, S., Feng, X., He, X. and Zimmerman, J., 2010. The biomechanical properties of concussions in high school football. Medicine and science in sports and exercise, 42(11), p.2064
  15. Greenwald, R.M., Gwin, J.T., Chu, J.J. and Crisco, J.J., 2008. Head impact severity measures for evaluating mild traumatic brain injury risk exposure. Neurosurgery, 62(4), pp.789-798
  16. Funk, J.R., Duma, S.M., Manoogian, S.J. and Rowson, S., 2007. "Biomechanical risk estimates for mild traumatic brain injury." Annual Proceedings/Association for the Advancement of Automotive Medicine. Vol. 51.
  17. Fréchède, B. and McIntosh, A.S., 2009. Numerical reconstruction of real-life concussive football impacts. Medicine and science in sports and exercise, 41(2), pp.390-398
  18. Ommaya, A. K., Yarnell, P., Hirsch, A. E., and Harris, E. H., 1967, ‘‘Scaling of experimental data on cerebral concussion in sub-human primates to concussion threshold for man,’’ Proceedings, 11th Stapp Car Crash Conf., SAE Paper No. 670906.
  19. Kuo, C., Wu, L., Loza, J., Senif, D., Anderson, S. C., & Camarillo, D. B. (2018). Comparison of video-based and sensor-based head impact exposure. PloS one, 13(6), e0199238.