Documentation:Repsponse test

Preview - Lit Review

Due to the tendency to cause severe injuries, boxing has drawn the attention of the public. Researchers have also done a tremendous amount of work attempting to understand the fundamental mechanisms behind injury endured in boxing and develop protective devices such as headgear to attenuate the impact. In this article, we will go through three major areas summarized from our extensive literature search result: 1). measurements of biomechanical properties in boxing, 2). headgear used in boxing, and 3). comparison between boxing and other combat sports. The first part will walk us through the biomechanical properties of boxing: peak linear and rotational acceleration, impact speed, peak force, as well as others, and how they are measured. The second part will focus on headgear used in boxing by investigating how well it can protect athletes, and also compare headgear used in boxing and used in other combat sports such as taekwondo. The last part will compare the biomechanical characteristics of boxing with other combat sports, including taekwondo and karate, and their various fighting skills altogether. At the end of this article, we will summarize our findings from these collected research papers by exploring their strengths, limitations, controversies, and future directions.

Protective Headgear

Headgear plays a critical role in attenuating the impact and increasing the protection of the boxers. This section will show some previous research on comparing the biomechanical response between wearing and not wearing headgear, comparing headgear used in boxing and other combat sports such as taekwondo, and then concludes with a discussion on the strengths, controversies, limitations, and future directions for this sub-area.

With vs. Without Headgear

Andrew S McIntosh and Declan A Patton (2015) provided an approach for measuring how well a boxing headgear can attenuate the head impact. In this approach, a spring driven linear impactor (shown in Figure 6.) was used to create a range of impacts at different speeds (between 4.1 and 8.3 m/s) and delivered the impacts to an instrumented Hybrid III Crash Test Dummy head and neck complex system with and without an AIBA (Association Internationale de Boxe Amateur)-approved headgear. The mass of the linear impactor was about 4 kg and a semi-rigid fist-glove interface was used to imitate more realistic boxing punches. Acceleration data show that there were large and/or significant differences in head-impact responses in the lateral and frontal tests between the AIBA-approved headgear and bare headform. More specifically, the following things were observed:

1) In the 8.3 m/s fist-glove impacts, mean peak resultant linear accelerations for bare headform were approximately 130 g compared with roughly only 85 g wearing the headgear.

2) In the 6.85 m/s fist-glove impacts, mean peak resultant angular head accelerations for bare headform were in the range of 5200–5600 rad/s^2 and nearly halved by wearing the headgear.

3) Linear and angular accelerations in 45° forehead and 60° jaw impacts were both reduced by the headgear to a large extent.

Overall, the article shows that existing AIBA-approved headgear can play a significant role in reducing head impact and the risk of head injury (measured by HIC15) in competitive boxing events where punch-speeds range from 5 to 9 m/s.

Figure 6. A: Disc-pad vs. B: Fist-glove interface used in a spring-driven linear impactor. DOI: 10.1136/bjsports-2015-095094

Boxing vs. Taekwondo Headgear

Aside from comparing the attenuation performance with vs. without headgear, DM O'Sullivan et al. (2016) compared the impact attenuation performance of boxing vs. taekwondo headgear by measuring the head's peak linear and rotational acceleration in a more recent study. A standardized martial arts headgear rotating striker (shown in Figure 7.) was used to impart impacts to a Hybrid III Crash Test Dummy head and neck complex system. Two boxing (Adidas and Greenhill) and two taekwondo (Adidas and Nike) headgear were selected and were fitted to the dummy head. For each headgear, the head was subsequently subjected to five impacts at the front and side locations by the striker at a speed of 8 ± 0.3 m/s. Linear and rotational acceleration were recorded throughout the experiment. The article' s results show that:

1) None of the headgear was able to pass the American Society for Testing and Materials (ASTM) criterion to reduce head acceleration below the cut-off threshold at 150 g.

2) There were significant interactions of the impact location and headgear brand on the rotational acceleration.

3) There were significant effects of both impact location and headgear brand on the linear acceleration.

4) Pairwise comparisons adjusted by Bon-ferroni correction show significant differences between the front and side locations for both linear and rotational acceleration.

The authors also indicated in the paper that increases in the thickness of headgear padding did not always correspond with a reduction in head acceleration. This points out that future studies should focus more on examining material properties that may increase headgear’s impact reduction to help better protect athletes in boxing, taekwondo, and other combat sports.

Figure 7. The rotating striker used for comparing boxing and taekwondo headgear. DOI: 10.1080/17461391.2016.1161073

Discussion

Strengths

These two papers aimed at investigating 1). how well headgear can protect the boxer's head and 2). the effect of wearing different headgear. Altogether they looked into several different punch regions: forehead (both), side (both), and jaw (one).

Controversies

The two papers both used Hybrid III dummy head for the test and they used punch speeds around 8 m/s (both) and around 7 m/s (one). However, under similar speed conditions (8 m/s), the first paper has a much lower linear acceleration result (< 100 g) compared to the second one (> 200 g). The linear acceleration variance could be caused by inconsistent ways used to create the impact load, inconsistent mass of the impactor (~4 kg vs. 4.5 kg), inconsistent mechanical properties of the headgear, whether the ‘fist’ interface wears a glove, whether the dummy head and neck complex were mounted to the body structure, and a lot of other considerations. In a nutshell, the inconsistent results in linear acceleration between the two papers show that the specific way a boxing-punch test is set up has a significant influence on the final outcome and data measured.

Limitations

The existing industry-recognized cut-off criterion mainly uses head linear acceleration. Standards on head rotational acceleration for boxing needs to be established in the future as well. Finally, the biofidelity of Hybrid III has never been verified for a boxing-punch scenario, which makes measurements in these two papers questionable in terms of how biofidelic the head's responses were. As we could imagine, punches on the head are not exactly the same as experiencing head impacts in frontal car crashes. New dummies for boxing studies might need to be developed to resolve this concern.

Future directions

In the future, we hope that a more consistent test platform for boxing-injury-biomechanics research can be developed such that people can share and compare their results more reasonably and objectively. Furthermore,

Introduction - E-Textbook

Based on the report from the National Safety Council, automobile accidents are one of the leading causes of death for all age groups. Among all injuries in automobile accidents, head injuries have been estimated to constitute approximately 71%. Therefore, various quantitative methods have been proposed and developed to evaluate the severity of head injuries. One of the most common criteria is Head Injury Criterion (HIC) which measures the head impact according to the mechanical input: linear resultant acceleration. In particular, this criterion has a long-time history of being used in evaluating the head injury risk in frontal car crashes. The official HIC limit value documented in National Highway Traffic Safety Administration (NHTSA) are computed from acceleration data collected at the head of Anthromorphic Test Devices (ATD) seated in a car. Besides HIC, there exist various other head injury criteria based on other types of mechanical inputs, for example, rotational acceleration, which includes Generalized Acceleration Model for Brain Injury Threshold (GAMBIT), Head Injury Power (HIP), Rotational Injury Criterion (RIC), and stress and strain, which includes Cumulative Strain Damage Measure (CSDM), Dilatation Damage Measure (DDM), and Relative Motion Damage Measure (RMDM). In this article, we solely focus on HIC because it paves the way for subsequent head injury criteria development in this area, and it is one of the most influential criteria used.

Head Injury Criterion (HIC)

History

In 1943, researchers, E. S. Gurdjian and J. E. Webster, at Wayne State University did one of the first studies that look into head injury mechanisms using dogs as animal models. Starting in 1961, cadavers were used to study the head injury mechanisms by E. S. Gurdjian, H. R. Lissner, which led to the creation of the well-known Wayne State Tolerance Curve (WSTC). The curve was hand-drawn through all the data points collected from cadaver drop tests (shown in Figure 1). WSTC captures the relationship between the magnitude of linear anterior-posterior acceleration and load duration. It also served as the foundation for the Gadd Severity Index (GSI) and HIC. In 1971, Versace developed the modern version of HIC as a method to measure mean acceleration that correlates with the WSTC. Then, HIC was proposed to replace GSI in Federal Motor Vehicle Safety Standards (FMVSS) No.208 by the NHTSA. On October 18, 1986, NHTSA proposed to constrain the HIC interval to 36 ms. Later on, NHTSA also proposed to evaluate HIC performance over 15 ms interval, scale HIC to various occupant sizes, and create the injury risk curve for HIC.

Figure 1. Wayne State Tolerance Curve (WSTC) DOI: 10.1242/dmm.011320

Mathematical Definition

HIC is formulated analytically as the following:

$HIC=\max _{t_{1},t_{2}}\left({\frac {1}{t_{2}-t_{1}}}\int _{t_{1}}^{t_{2}}a(t)dt)\right)^{2.5}(t_{2}-t_{1})$

where $a(t)$ is the linear resultant acceleration (described in gravity unit, $g$). Assume the entire time duration of the acceleration is $T$ (in seconds), $t_{1}$ and $t_{2}$ are two time points within in the impact ($0\leq t_{1}\leq t_{2}\leq T$). The optimal interval $[t_{1},t_{2}]$ that maximizes HIC value is called the HIC interval and they are not necessarily unique. In typical car crash tests (citation here), time intervals of the head impact ranges from 50 - 200 ms and are normally sampled at a frequency from 0.625 - 12.5 kHz.

Major Limitation

One of the biggest concerns of using HIC is that it solely uses linear acceleration measurements to compute its value, lacking a consideration on other important factors that contribute to skull fracture injury such as rotational acceleration, location and area of the impact, and etc.

Applications

HIC is used extensively in vehicle safety as a major performance index to evaluate the risk of head injury, especially in frontal impacts. In FMVSS No.208 and FMVSS No.213, the upper limit HIC value is set to 1000 for a maximum of 36 ms interval and 700 for a maximum of 15 ms interval, under the condition that a Hybrid III dummy head moving at 15 mph to impact the interior of a vehicle. HIC36 is the old standard whereas HIC15 is the current standard.

HIC is also referenced in the New Car Assessment Program (citation here) , which is a car safety program that evaluates new automobile designs against different types of safety threats. Not only the automobile industry, but the aircraft industry (citation here) also regulates certifications according to certain HIC requirements. In the Head Injury Risk Curve (Figure 2), which was developed from cadaver drop tests, the probability of causing a MAIS >= 2 injury is mapped to a HIC value ranging from 0 to 3000. From this curve, HIC value at 1000 implicates a risk at around 50% of MAIS >= 2 injury. It is also mentioned in the report that HIC value at 700 represents a 31% probability of MAIS >= 2 injury.

Figure 2. Head Injury Risk Curve, indicating the probability of MAIS >= 2 injuries. NHTSA report

Besides vehicle safety, HIC is actively used in different sports. The major one is contact sports such as hockey (citation here), soccer (citation here), American football (citation here), lacrosse (citation here), as well as many others to help better design helmets and protect athletes from head injuries. Other types of sports include motorsports (citation here), cycling (citation here), and horse riding (citation here), which all tend to bear the possibility of resulting in head injuries.