بررسی و تحلیل عوامل خطرزای آسیب مغزی در یک ضربه مشت مستقیم بوکس

Background and Purpose
Brain injury is a complex pathophysiological process resulting from severe biomechanical impacts to the head, neck, or face, leading to neurological dysfunction and potentially long-term cognitive and physical impairments. In contact sports such as boxing, athletes are frequently exposed to repeated blows, which significantly increase the risk of brain injuries, including concussions and more severe traumatic brain injuries (TBI). Understanding the biomechanical factors that contribute to brain injury is crucial for developing effective injury prevention strategies and designing protective equipment such as helmets.
The primary mechanical causes of brain injury are linear and rotational accelerations of the head. Linear acceleration refers to the straight-line movement of the head, while rotational acceleration involves angular movement around an axis. Both types of acceleration can cause different injury mechanisms within the brain tissue, including diffuse axonal injury and vascular damage. During combat sports, athletes often instinctively alter their head and neck positions to mitigate or evade impacts. These positional changes can influence the magnitude and direction of linear and rotational accelerations experienced by the brain, thereby affecting injury risk.
This study aimed to investigate the effects of linear and rotational accelerations, as well as head-neck orientation, on brain injury risk in boxing. Specifically, it sought to quantify how different head and neck angles during impact influence the magnitude of accelerations and their components, and to compare these values against established injury thresholds.
 Materials and Methods
A computer simulation approach was employed using Adams software (version 2013, MSC Software, California, USA) to model the biomechanical interactions of the head, neck, and punch during boxing impacts. The head and neck were modeled as rigid bodies connected by joints with defined biomechanical properties, and the punch was simulated as an external force applied at various angles.
Head and neck orientations were determined using inverse kinematics and Euler ZXZ angles, which allowed precise control over the three-dimensional positioning of the head relative to the neck. Punches were simulated at lateral and anterior-posterior angles of 0°, 5°, 10°, and 15°, representing realistic variations in impact direction during a boxing match.
For each simulated punch, linear and rotational accelerations of the head were measured. Linear acceleration components (ax, ay, az) corresponded to movements along the x, y, and z axes, while rotational acceleration components (rx, ry, rz) corresponded to angular accelerations about these axes. Data were collected for each head-neck orientation and compared to known injury thresholds from the literature.
 Results
The simulation results revealed several important trends in how head and neck orientation affects acceleration magnitudes:
Linear Acceleration: The maximum linear acceleration (amax) and its primary component in the frontal plane (ay) decreased with increasing neck angle θ. Conversely, the az component showed a symmetrical increase on both sides of the neck with increasing θ, reaching values of approximately 441.84 m/s² at 15°. The ax component exhibited asymmetry: on the left side of the neck, ax increased with θ, while on the right side it decreased. These asymmetries highlight the complex biomechanical behavior of the neck and head during impacts.
Rotational Acceleration: The rotational acceleration component rz increased significantly with increasing head flexion angle ɸ, rising from 155 rad/s² to 1155 rad/s² at 15°. This rapid increase, although still below established injury thresholds, suggests that small changes in head flexion can substantially raise brain injury risk. The rx component showed a slight decrease (6.15%) at 15°, while ry remained relatively constant regardless of turning direction. Notably, the rz component exhibited opposite trends on the left and right sides of the neck, increasing on the right and decreasing on the left.
Symmetry and Asymmetry:
The study found both symmetrical and asymmetrical patterns in acceleration components depending on the side of the neck and the angle of head flexion or rotation. These findings underscore the importance of considering individual biomechanical variability when assessing brain injury risk.
Injury Thresholds:
Peak rotational accelerations reached 4036 rad/s², with average rotational accelerations around 1140 rad/s². Prior research indicates that rotational accelerations exceeding 4500 rad/s² can cause cerebral vein rupture, while 1800 rad/s² is associated with a 50% risk of concussion. Although the measured values in this study were below these thresholds, the increasing trend in rz with head flexion angle suggests that even slight increases in angle could push accelerations into dangerous ranges during repeated impacts.
Linear Acceleration and Injury Risk:
The maximum linear acceleration measured did not, by itself, indicate a serious immediate risk for brain injury. However, the study notes that repeated exposure to such accelerations may reduce brain tissue tolerance due to cumulative stretching and strain, potentially increasing injury risk over time.
Discussion
This study highlights the critical role of rotational acceleration, particularly the rz component in the sagittal plane, as a biomechanical risk factor for brain injury in boxing. The findings suggest that head and neck orientation during impacts significantly modulates the magnitude and direction of these accelerations, which may influence injury severity.
The asymmetrical behavior of acceleration components emphasizes the need for individualized assessment in injury prevention and protective equipment design. For example, training athletes to maintain optimal head and neck positions during combat may mitigate harmful accelerations.
The rapid increase in rotational acceleration with small changes in head flexion angle underscores the importance of neck strength and control in reducing brain injury risk. Conditioning programs focusing on neck musculature could enhance athletes’ ability to stabilize the head during impacts.
Given that linear accelerations alone did not reach injury thresholds, but rotational accelerations approached critical levels, protective strategies should prioritize reducing rotational forces. Helmet design and rule modifications in boxing could focus on minimizing rotational acceleration transmission.
 Conclusion
The research concludes that rotational acceleration and head-neck orientation in the sagittal plane are significant biomechanical risk factors for brain injury in boxing athletes. While linear acceleration did not reach levels associated with immediate injury, the cumulative effect of repeated impacts and the increase in rotational acceleration components, especially rz, pose a substantial risk.
These findings have important implications for injury prevention, athlete training, and equipment design. Educating athletes about optimal head and neck positioning, enhancing neck strength, and developing protective gear that attenuates rotational forces could reduce the incidence and severity of brain injuries in boxing.
Future studies should incorporate more complex, multi-impact simulations and consider individual anatomical variability to better understand cumulative brain injury mechanisms in combat sports.
Article Message
Boxing athletes experience high rotational accelerations during punches, particularly influenced by head and neck orientation in the sagittal plane, which significantly increases the rz component of rotational acceleration. This biomechanical factor likely elevates the risk of brain injury, underscoring the need for targeted prevention strategies focusing on neck positioning and rotational force mitigation.