Background and Purpose
The risk of brain injuries, especially in competitive and championship sports, is an undeniable fact. In order to reduce the risk of brain injury, much research has been conducted on the biomechanics of brain injury, in which various injury assessment criteria have been proposed for different types of head injuries.
In contact sports, most head injury criteria are evaluated based on the kinematic response of the head to impact. In impact sports such as taekwondo, boxing and other impact sports, when a blow is made to the head, both linear acceleration and rotational acceleration are produced simultaneously in the head, and this can possibly change the threshold of head injury compared to the case where each of these criteria is considered separately. As mentioned earlier, this issue has not been considered in previous studies. Therefore, this study intends to examine combined criteria in addition to examining injury from the perspective of single-parameter criteria such as linear acceleration and rotational acceleration. The purpose of this study is to investigate and analyze the single-parameter criteria of linear acceleration and rotational acceleration and the GAMBIT multi-parameter criterion in head injury in impact sports.
 
Methods
In this study, in order to evaluate GAMBIT in contact sports, first, information from previous studies (linear acceleration and rotational acceleration) in the field of head injuries in boxing, taekwondo, wrestling, judo and MMA was collected. For this purpose, there was a need to first model a blow to the head in martial arts, so modeling from previous research was used.
After collecting the information, those parameters that were not included in previous studies were simulated and calculated using Adams software.
With an appropriate and reliable model, it is possible to examine and complete the results of other research in this field. In order to ensure the accuracy and precision of the modeling of this study, a direct punch in boxing and a rotational leg kick in taekwondo were simulated in accordance with previous studies and their results were compared with each other. After comparing the results of previous experiments with the simulation method in this study and ensuring its accuracy, this model was used to continue the work and simulate the parameters required in this study. After collecting and obtaining the accelerations from previous studies, the GAMBIT criterion was also obtained in the MATLAB program. Finally, the linear acceleration, rotational acceleration, and GAMBIT criteria and their injury threshold values ​​in impact sports were examined and analyzed.
 
Results
The results of the modeling validation of the present study, with an error range of 2.9% to 4.8%, indicate the validity of the modeling of this study, which can be relied on for simulation. Since each study was conducted with a different method and unique materials and computational techniques were used, it is obvious that there is a percentage difference between different methods and studies.
According to the results of this study, the most research conducted in the field of head impact in martial arts is in boxing, taekwondo, judo, and MMA, respectively. The results also showed that the rotational acceleration produced in the head has its highest value in taekwondo (5251.78 rad/s2), MMA (5172.70 rad/s2), boxing (4951.53 rad/s2), and judo (1889.66 rad/s2), respectively. The rotational acceleration generated in different martial arts with the injury thresholds given in the references was compared and the occurrence of injury in these cases was examined.
A review of previous research showed that the highest linear acceleration produced in the head due to impact in martial arts is in taekwondo (142/42 g). After that, boxing (86/66 g), judo (61/35 g), and MMA (50/55 g) showed the highest value, respectively. By simultaneously considering linear and rotational accelerations in the GAMBIT equation, a new criterion for the threshold of brain injury in each sport was obtained. In the study, the highest GAMBIT values ​​were determined for taekwondo (0.57), boxing (0.38), MMA (0.27), and judo (0.25), respectively. And the damage threshold was also plotted from the point of view of the GAMBIT composite criterion.
 
Conclusion
In the study of the mechanism of head injury, it was shown that two types of impact and non-impact loading can be distinguished, each of which leads to different responses in the head. In impact loading, the impact force is considered the cause of the injury. In non-impact situations, the head is loaded only as a result of the force resulting from inertia, i.e. acceleration. This acceleration can be linear or rotational, with linear acceleration leading to local damage and rotational acceleration leading to diffuse and extensive brain damage.
In comparing the gambit achieved in each discipline with its tolerance criterion, the red line shows the gambit injury threshold, according to which the gambits achieved in combat sports are lower than the head injury threshold. In general, the closer the gambit value is to unity, the greater the risk of injury to the athlete's head. In general, in the comparison of the four disciplines, the amount of gambit in taekwondo was higher but it was not exposed to the threshold of head injury, which is probably due to the fact that the time parameter was not taken into account in the calculations and the criteria and threshold of injury. However, in determining the threshold of injury by a criterion such as HIC, time is also taken into account and calculated, and this duration of contact in the impact is very important from the perspective of momentum and impact severity.
The comparisons made with the thresholds of injury have several points. First, the threshold of injury in the study using single-parameter criteria is much lower than the threshold of injury in multi-parameter criteria, and this could be due to the occurrence of injury through a secondary parameter during the determination of the threshold of injury by the main parameter that was outside the calculations of the researchers. Another point in observing the difference in response to injury in the study using different parameters could be different definitions of the type and nature of head injury, the use of different measuring devices for these injuries, or errors in recording this information, which indicates the need to review and conduct more detailed medical and clinical studies in recording these criteria and thresholds. Because the accuracy in defining these thresholds, along with strict considerations, can change the boundaries of the definition of injury and, consequently, sports standards, performance techniques in contact sports, and materials used in protective sports clothing. Finally, it can be suggested that a more comprehensive and complete multi-parameter criterion be considered and injury thresholds be determined according to it.
 
Article Message
The results of this study showed that considering each of the linear and rotational accelerations alone, in the assessment of head injury in martial arts, the rotational acceleration is higher than the threshold for head injury, which was higher in taekwondo. However, considering the Gambit criterion in examining the threshold for head injury, it was found that blows to the head in martial arts do not expose athletes to head injury. To obtain more information about the Gambit criterion, more research is needed, such as laboratory studies and the use of subjects, which is suggested to be considered by researchers in the future.
Ethical Considerations
Since no subjects were used in this study and the data and results were based on previous studies, computer simulations, and programming outputs, there was no need to obtain a code of ethics from the competent authorities.
Authors’ Contributions
Conceptualization: Boroushak and Khoshnoodi
Data Collection: Khoshnoodi and Boroushak
Data Analysis: Khoshnoodi and Boroushak
Manuscript Writing: Boroushak and Khoshnoodi
Review and Editing: Khoshnoodi
Responsible for funding: Boroushak
Literature Review: Boroushak and Khoshnoodi
Project Manager: Boroushak
Any other contributions: Computer simulation and programming were performed by Dr. Khoshnoodi.
Conflict of Interest
No conflict of Interest.
Acknowledgments
This article is an extract from the research project of Dr. Neda Broshak at the Institute of Physical Education and Sport Sciences of Iran. The authors of this article are grateful for the material and moral support of the Institute.