Boxing and mixed martial arts: preliminary traumatic neuromechanical injury risk analyses from laboratory impact dosage data

Laboratory investigation

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Object

In spite of ample literature pointing to rotational and combined impact dosage being key contributors to head and neck injury, boxing and mixed martial arts (MMA) padding is still designed to primarily reduce cranium linear acceleration. The objects of this study were to quantify preliminary linear and rotational head impact dosage for selected boxing and MMA padding in response to hook punches; compute theoretical skull, brain, and neck injury risk metrics; and statistically compare the protective effect of various glove and head padding conditions.

Methods

An instrumented Hybrid III 50th percentile anthropomorphic test device (ATD) was struck in 54 pendulum impacts replicating hook punches at low (27–29 J) and high (54–58 J) energy. Five padding combinations were examined: unpadded (control), MMA glove–unpadded head, boxing glove–unpadded head, unpadded pendulum–boxing headgear, and boxing glove–boxing headgear. A total of 17 injury risk parameters were measured or calculated.

Results

All padding conditions reduced linear impact dosage. Other parameters significantly decreased, significantly increased, or were unaffected depending on padding condition. Of real-world conditions (MMA glove–bare head, boxing glove–bare head, and boxing glove–headgear), the boxing glove–headgear condition showed the most meaningful reduction in most of the parameters. In equivalent impacts, the MMA glove–bare head condition induced higher rotational dosage than the boxing glove–bare head condition. Finite element analysis indicated a risk of brain strain injury in spite of significant reduction of linear impact dosage.

Conclusions

In the replicated hook punch impacts, all padding conditions reduced linear but not rotational impact dosage. Head and neck dosage theoretically accumulates fastest in MMA and boxing bouts without use of protective headgear. The boxing glove–headgear condition provided the best overall reduction in impact dosage. More work is needed to develop improved protective padding to minimize linear and rotational impact dosage and develop next-generation standards for head and neck injury risk.

Abbreviations used in this paper:ATD = anthropomorphic test device; CSDM05 = cumulative strain damage measure at the 0.05 level; DDM = dilatational damage measure; GAMBIT = Generalized Acceleration Model for Brain Injury Threshold; GSI = Gadd Severity Index; HIC = Head Injury Criterion; HIP = head impact power; MMA = mixed martial arts; RMDM = relative motion damage measure; SIMon = Simulated Injury Monitor; wPCS = weighted principle component score.

Abstract

Object

In spite of ample literature pointing to rotational and combined impact dosage being key contributors to head and neck injury, boxing and mixed martial arts (MMA) padding is still designed to primarily reduce cranium linear acceleration. The objects of this study were to quantify preliminary linear and rotational head impact dosage for selected boxing and MMA padding in response to hook punches; compute theoretical skull, brain, and neck injury risk metrics; and statistically compare the protective effect of various glove and head padding conditions.

Methods

An instrumented Hybrid III 50th percentile anthropomorphic test device (ATD) was struck in 54 pendulum impacts replicating hook punches at low (27–29 J) and high (54–58 J) energy. Five padding combinations were examined: unpadded (control), MMA glove–unpadded head, boxing glove–unpadded head, unpadded pendulum–boxing headgear, and boxing glove–boxing headgear. A total of 17 injury risk parameters were measured or calculated.

Results

All padding conditions reduced linear impact dosage. Other parameters significantly decreased, significantly increased, or were unaffected depending on padding condition. Of real-world conditions (MMA glove–bare head, boxing glove–bare head, and boxing glove–headgear), the boxing glove–headgear condition showed the most meaningful reduction in most of the parameters. In equivalent impacts, the MMA glove–bare head condition induced higher rotational dosage than the boxing glove–bare head condition. Finite element analysis indicated a risk of brain strain injury in spite of significant reduction of linear impact dosage.

Conclusions

In the replicated hook punch impacts, all padding conditions reduced linear but not rotational impact dosage. Head and neck dosage theoretically accumulates fastest in MMA and boxing bouts without use of protective headgear. The boxing glove–headgear condition provided the best overall reduction in impact dosage. More work is needed to develop improved protective padding to minimize linear and rotational impact dosage and develop next-generation standards for head and neck injury risk.

Historically, linear acceleration has been the main parameter by which to measure athletic head injury risk; however, combinations of linear and rotational impact dosage have been widely acknowledged as contributors to head injury. Current standard head injury metrics—the GSI9 and HIC35—are based on resultant linear head center of gravity acceleration and cannot be used to quantify rotational injury risk. These injury metrics were developed from laboratory head impact studies conducted decades ago and were correlated to severe skull fracture and brain injury, but not less-severe brain injuries like concussion. As HIC, GSI, and resultant linear head center of gravity acceleration are the most widely used and only currently mandated injury metrics for athletic head-padding impact testing,1,19,28 little research has been conducted on boxing and mixed martial arts (MMA) padding effects on rotational or combined impact dosage injury risk. Therefore, while boxing and MMA padding may be capable of reducing linear impact dosage (for example, GSI, HIC, linear acceleration, and impact force), the effects of padding on rotationally induced head or neck injury risks remain unclear. Finally, there has been a call for an end to the use of the HIC, a linear acceleration–based criterion derived from the GSI, as a head injury risk quantifier.16

Several investigators have studied athletic padding in sports such as American and Australian football, boxing, soccer, rugby, and equestrian events. In these sports, impacts have been replicated using humanoid head forms, anthropomorphic surrogates, volunteers, or cadavers in impacts with kinetic energy from 9 J to 354 J.3,10,12–14,17,18,20,26,34,37,40 With the exception of one American football helmet study39 and one study of jockey and other equestrian helmets,10 rotational head impact dosages have not been reported. Interestingly, many studies reported variable linear responses, with some padding increasing and other padding decreasing linear kinematic parameters such as GSI, HIC, and head acceleration.3,7,18,20,26,34,37,40 A study of American football helmets demonstrated that linear and rotational impact dosages were no different in newer helmets and a widely used conventional helmet.37 Most importantly, authors of several studies reported that none of the padding models tested provided adequate head injury protection when impacts were compared with bare head impacts.12,18,34,39 Many studies have also indicated that padding thickness, padding composition, and contact friction play important roles in reducing head and neck injury risk.7,10,12,18,34,40 Because of these varying head impact attenuation characteristics of athletic padding and the lack of data on padding effects on head and neck injury risk, additional investigations regarding the effects of padding on rotational impact dosage and head and neck injury risk are needed.

Methods

We investigated linear, rotational, and combined impact dosages of selected boxing and MMA padding gear during a series of 54 pendulum impacts at low (27–29 J) and high (54–58 J) energy to the lateral head of an instrumented Hybrid III 50th percentile ATD (Humanetics Innovative Solutions). The pendulum impacts were engineered to replicate severe hook punches. A total of 5 padding combinations were examined: 1) unpadded (control), 2) MMA glove–unpadded head, 3) boxing glove–unpadded head, 4) unpadded pendulum–boxing headgear, and 5) boxing glove–boxing headgear. From these tests, a total of 17 established and proposed head and neck injury risk impact dosage parameters were measured or calculated.

A Hybrid III 50th percentile ATD was instrumented with a triaxial linear accelerometer (Model EAS3–250, Measurement Specialties) rigidly mounted at the head center of gravity and triaxial angular velocity sensor (Model ARS-06S, ATA Sensors) mounted adjacent to the accelerometer. A 6-channel upper neck load cell (Model 1716A, Denton ATD) measured forces and moments in 3 directions. Moments measured by the load cell were translated to the occipital condyles by multiplying respective x and y axis shear forces via the 1.778-cm moment arm. A triaxial linear accelerometer was mounted in the ATD chest to ensure minimal thoracic motion during impact. All data were collected at 5000 Hz, filtered according to SAE J21130 and sign convention (direction of positive x, y, and z axes) adhered to SAE J1733.29 Angular acceleration was calculated via filtered angular velocity signal differentiation. The ATD head weighed 5.1 kg with instrumentation, the cervical spine weighed 1.6 kg, and the ATD torso and upper extremities weighed 21.2 kg.

A steel sphere was precisely machined to create a 3.6-kg pendulum impactor mass. The mass was chosen to approximate the effective upper-extremity mass of volunteer boxers during similar punch testing.38 A steel eye hook was threaded into the flat machined face, and the impactor was balanced such that the mass moment of inertia was translated only in the vertical direction. The same steel sphere was used in all trials. A 6.4-mm steel braided cable was hung from a free-swinging carabiner secured to a ceiling strut located approximately 5 m directly above the center of gravity of the ATD head. The ATD was secured to a test stand with tie-down straps and the lower extremities were removed at the femur. Inertial responses were further minimized by securing the test stand with 3500 N of sandbags. The pendulum mass was raised into position via nylon fishing line with 220 N rupture strength, tied to the eye hook, and routed through a ceiling-mounted pulley aligned with the head center of gravity, normal to the lateral ATD head surface.

In each head impact trial, the pendulum mass was raised to 0.76 m or 1.52 m and the nylon line was cut with a pair of scissors. The swing heights were selected to recreate low- and high-energy impacts on par with boxing punches to the lateral ATD head from prior boxing studies (Pincemaille Y, presented at the 33rd Stapp Car Crash Conference, 1989)27,31,36 and in the range of impact dosage proposed to cause head and neck injury.4,6,8,11,15,21–25,33,41

Tuf-Wear training headgear (0.63 kg), an Everlast Pro Style boxing training glove (0.27 kg), and a UFC Official MMA glove (0.18 kg) were tested. The boxing and MMA gloves were firmly affixed to the pendulum via a combination of double-sided tape on the mass and gaffer's tape on the exterior. The headgear was secured with double-sided tape on the head and by cinching taut the chinstrap and superior-posterior lacing. The 5 impact conditions are described in Table 1 and shown in Figs. 15.

TABLE 1:

Impact matrix

ConditionImpact Energy (J)Impact Momentum (N-sec)
LowHighLowHigh
unpadded (control)27541420
unpadded pendulum–headgear27541520
MMA glove–bare head28561521
boxing glove–bare head29581421
boxing glove–headgear5821
Fig. 1.
Fig. 1.

Photograph demonstrating the unpadded (control) impact condition.

Fig. 2.
Fig. 2.

Photograph showing the bare pendulum–headgear condition.

Fig. 3.
Fig. 3.

Photograph of the MMA glove–bare head condition.

Fig. 4.
Fig. 4.

Photograph showing the boxing glove–bare head condition.

Fig. 5.
Fig. 5.

Photograph demonstrating the boxing glove–headgear condition (high-energy trial only).

A total of 6 trials were conducted for the 5 impact conditions and the 2 impact energy levels resulting in a total of 54 impacts. The boxing glove–boxing headgear condition was omitted in the low-energy condition. The 6 trials at each swing height were performed in an effort to measure the coefficient of variability and determine statistical power for future testing. Unpadded head impacts served as the control for each condition. Because all impacts were laterally directed, the resultant values were analyzed and individual x, y, and z axis components were not examined separately.

For each impact condition, impact dosage was quantified via 17 relevant dynamic head and neck injury risk parameters that are discussed in depth in the Appendix. The parameters were grouped into linear, rotational, and combined groups, as shown in Table 2. Some of the more complex parameters included empirical injury risk criteria that were calculated post hoc, including the HIC,35 GSI,9 Generalized Acceleration Model for Brain Injury Threshold (GAMBIT) (Newman JA, presented at the International Conference on the Biomechanics of Impact, 1986), weighted principle component score (wPCS),11 and head impact power (HIP).22 The HIC and GSI are calculated injury risk functions based on time-varying linear acceleration at the head center of gravity. The GAMBIT, wPCS, and HIP are calculated injury risk functions based on time-varying linear acceleration at the head center of gravity and rigid body angular acceleration. The wPCS has additional empirical relationships that consider GSI and HIC with numerical scaling and offset constants.

TABLE 2:

Impact dosage parameters*

ParameterUnits
linear parameters
 linear accelerationg
 GSINA
 impact durationsec
 linear momentum transferN-sec
 neck forceN
 impact forceN
rotational parameters
 angular velocityrad/sec
 angular accelerationrad/sec2
 angular momentum transferN-m-sec
 neck momentN-m
combined parameters
 kinetic energy transferJ
 GAMBITNA
 wPCSNA
 HIPNA
 CSDM05NA
 RMDMNA
 DDMNA

* NA = not applicable.

Furthermore, linear head center of gravity acceleration and angular velocity were used as inputs to the Simulated Injury Monitor (SIMon) brain injury risk software32 (V3.051, National Transportation Biomechanics Research Center). The SIMon model consists of a 3D skull and brain with rigid skull, dura-CSF layer, falx cerebri, brain matter, and bridging veins.2,32 The model represents the 50th percentile male with a head mass of 4.7 kg—approximating that of the Hybrid III 50th ATD. There are 10,475 nodes and 7852 elements, with 7776 hexagonal and 76 beam elements. At each time step, SIMon calculates 3 theoretical brain injury risk metrics: 1) the cumulative strain damage measure (CSDM05), 2) the relative motion damage measure (RMDM), and 3) the dilatational damage measure (DDM). The CSDM05 is the cumulative percentage of brain volume experiencing at least 5% stretch over the duration of head impact loading. This 5% stretch value has been correlated with mild diffuse axonal injury (a result of significant angular brain motion) and transient depolarization.2,32 The RMDM results are an indication of the risk of sustaining acute subdural hematoma due to bridging vein rupture.2,32 More specifically, an RMDM value of 0.5 is equated with an 8% risk, an RMDM value of 1.0 is equated with a 50% risk, and an RMDM value of 2.0 is equated with a 98% risk of acute subdural hematoma. A third brain injury metric known as the DDM, which was developed as an estimate of vacuum contusions within brain tissue (Bandak FA, presented at the Stapp Car Crash Conference, 1994),2,32 was also calculated for all impacts.

The mean maximum value (mean of the maximum values from each of 6 trials) for each parameter (kinematic data, kinetic data, and SIMon) in each condition was used in a 2-tailed paired t-test comparison against the unpadded control condition. The null hypothesis was that the mean maximum values of the variables compared for each condition were equal. The alternative hypothesis was that the mean maximum values were not equal. A 5% significance (α = 0.05) level was used. This hypothesis was tested using a 2-sample Welch t-test, with unequal sample sizes and unequal variances, assuming a Student t-distribution and requiring the Satterthwaite approximation to determine degrees of freedom.

Results

In response to the hook punch impacts recreated by the impact pendulum, there was some variability in kinematic (linear head center of gravity acceleration, angular velocity) and kinetic (neck force, neck moment) independent variables during the sequence of 6 repeated impacts. As a means of quantifying this variability for the data collected, we have collated in Table 3 the respective coefficient of variation of each impact condition for the set of 6 repeated impact trials. The coefficient of variation was calculated by dividing the standard deviation from each set of 6 impacts by the mean value at the time of highest linear center of gravity acceleration resultant. In spite of best attempts to ensure consistent impacts, the average coefficient of variation shown in Table 3 varied from as low as 6.5% (unpadded control) to as high as 26.1% (boxing glove–boxing headgear). The boxing glove–boxing headgear trials demonstrated the highest variation.

TABLE 3:

Coefficient of variation of each resultant independent variable*

ParameterUnpadded (control)Unpadded Pendulum–HeadgearMMA Glove–Bare HeadBoxing Glove–Bare HeadBoxing Glove–Headgear
low energy
 linear acceleration4.76.911.812.4
 angular velocity10.324.610.019.9
 neck force7.421.122.016.9
 neck moment15.114.027.416.9
 average9.416.717.816.5
high energy
 linear acceleration2.14.313.59.937.7
 angular velocity12.729.010.29.333.3
 neck force3.55.910.89.323.3
 neck moment7.810.520.27.89.9
 average6.512.413.79.726.1

* Values taken at time corresponding to maximum linear acceleration.

The mean resultant values for ATD head center of gravity linear acceleration, head angular velocity, head angular acceleration, and impact force from the impact conditions are presented in Figs. 69. A representative example of the computational simulation results of the SIMon software32 used to generate CSDM, DDM, and RMDM brain injury risk measures is presented in Fig. 10.

Fig. 6.
Fig. 6.

Graphs illustrating the linear acceleration in the high-energy (upper) and low-energy (lower) trials.

Fig. 7.
Fig. 7.

Graphs showing the angular velocity in the high-energy (upper) and low-energy (lower) trials.

Fig. 8.
Fig. 8.

Graphs demonstrating the angular acceleration in the high-energy (upper) and low-energy (lower) trials.

Fig. 9.
Fig. 9.

Graphs illustrating the impact force in the high-energy (upper) and low-energy (lower) trials.

Fig. 10.
Fig. 10.

Representative frame from the SIMon computational simulation results displaying pressure isosurfaces within the brain from boxing glove–bare head impacts.

A total of 17 dynamic head and neck impact dosage parameters were then compared, via a 2-tailed t-test, to the unpadded control impacts for the low- and high-energy conditions. The results are summarized in Tables 4 and 5. (The maximum value for each of the parameters is shown.) Based on this t-test comparison with the unpadded control condition, parameters that were significantly lower at the p < 0.05 level are shaded and parameters that were significantly higher are shown in boldface. Because the DDM results reported by SIMon were near zero for all impacts, this parameter was not reported.

TABLE 4:

Maximum values from the low-energy trials*

ParameterUnpadded (control)Unpadded Pendulum–HeadgearMMA Glove–Bare HeadBoxing Glove–Bare Head
linear parameters
 head acceleration (g)15354.754.762.0
 GSI281514256
 impact duration (sec)0.00370.01570.01720.0136
 linear momentum transfer (N-sec)10.811.310.611.2
 neck force (N)778397478518
 impact force (N)8390308031903920
rotational parameters
 angular velocity (rad/sec)15.816.718.512.8
 angular acceleration (rad/sec2)4810296024402450
 angular momentum transfer (N-m-sec)0.2690.3050.3240.245
 neck moment (N-m)32.718.534.023.5
combined parameters
 kinetic energy transfer (J)11.612.711.010.9
 GAMBIT0.6240.2360.2300.257
 wPCS87.431.829.633.2
 HIP9720393036703860
 CSDM050.6060.3970.4480.195
 RMDM1.891.431.161.27
 DDM

* Values are means of the maximum values from 6 impacts for each condition. Boldface indicates significant increase (p < 0.05); dark shading indicates significant decrease (p < 0.05).

TABLE 5:

Maximum values from the high-energy trials*

ParameterUnpadded (control)Unpadded Pendulum–HeadgearMMA Glove–Bare HeadBoxing Glove–Bare HeadBoxing Glove–Headgear
linear parameters
 head acceleration (g)23212911714465.0
 GSI76826521931179
 impact duration (sec)0.00350.01140.01430.00730.0182
 linear momentum transfer (N-sec)15.215.515.316.315.9
 neck force (N)1,252746836868629
 impact force (N)12,7707,1606,6308,9004,240
rotational parameters
 angular velocity (rad/sec)18.522.626.216.318.3
 angular acceleration (rad/sec2)5,2605,5505,2403,8001,740
 angular momentum transfer (N-m-sec)0.3450.4060.4490.3210.364
 neck moment (N-m)48.834.047.738.242.4
combined parameters
 kinetic energy transfer (J)22.723.723.123.322.1
 GAMBIT0.9360.5410.4910.5830.264
 wPCS173.280.971.387.835.8
 HIP20,50012,70011,60012,7005,440
 CSDM050.6360.7740.8190.4520.210
 RMDM2.352.482.172.031.08
 DDMNANANANANA

* Values are means of the maximum values from 6 impacts for each condition. Boldface indicates significant increase (p < 0.05); dark shading indicates significant decrease (p < 0.05).

Low-Energy Results

As seen in Table 4, for the linear impact dosage t-test results, impact duration increased significantly (p < 0.05) from the unpadded control, whereas all other parameters except linear momentum (including linear acceleration and GSI) significantly decreased across all conditions. The MMA glove–bare head and unpadded pendulum–headgear conditions showed a significant increase in linear momentum transfer. While angular acceleration was significantly reduced in all 3 conditions compared with the unpadded control, angular velocity and angular momentum were significantly reduced in the unpadded pendulum–headgear condition only. Angular momentum was significantly increased in the MMA glove–bare head and boxing glove–bare head conditions. The neck moment was significantly reduced in the MMA glove–bare head and unpadded pendulum–headgear conditions, but not in the boxing glove–bare head condition. All of the low-energy combined impact dosage parameters were significantly decreased except for head kinetic energy in the MMA glove–bare head and boxing glove–bare head conditions, as well as the CSDM05 in the boxing glove–bare head condition.

High-Energy Results

In the high-energy tests (Table 5), impact duration was significantly increased (p < 0.05) across all conditions. The other linear impact dosage parameters, with the exception of linear momentum, were significantly reduced. The linear momentum showed a significant increase in 3 of the 4 high-energy conditions studied. The high-energy rotational impact dosage parameters were associated with greater variation than the low-energy comparisons. Angular velocity significantly increased in MMA glove–bare head and boxing glove–bare head conditions, significantly decreased with unpadded pendulum–headgear, and had no statistically significant difference in boxing glove–headgear conditions. Angular momentum results were the same with the exception of a significant increase in the boxing glove–headgear condition. Angular acceleration significantly decreased in the unpadded pendulum–headgear and boxing glove–headgear conditions but was no different in the MMA glove–bare head and boxing glove–bare head conditions. Neck moment was significantly reduced for the MMA glove–bare head and unpadded pendulum–headgear conditions but no different for the other 2 conditions. When examining the combined impact dosage parameter results, kinetic energy transferred to the ATD head was significantly higher for both the MMA glove–bare head and unpadded pendulum–headgear conditions. The calculated GAMBIT, wPCS, and HIP were significantly decreased versus the unpadded control values for all conditions. The CSDM was significantly reduced in the 2 headgear conditions, but significantly larger in the MMA glove–bare head and boxing glove–bare head conditions. Finally, the RMDM significantly decreased with the exception of the MMA glove–bare head condition.

Discussion

As a means to study boxing and MMA padding effects on head and neck injury risk, we preliminarily investigated 17 dynamic head and neck impact dosage injury risk parameters in a series of 54 low- and high-energy impacts to an instrumented Hybrid III ATD. Our impacts recreated real-world right hook punches to the left side of the head and involved 5 padding combinations: unpadded (control), MMA glove–bare head, boxing glove–bare head, unpadded pendulum–headgear, and boxing glove–headgear. Measured linear head acceleration (54.7–144 g), angular acceleration (1740–5550 rad/second2), angular velocity (12.8–26.2 rad/second), neck moment (18.5–47.7 N-m), and impact force (3080–8900 N) dosages were within ranges of theoretical head and neck injury limits.3,5,10,12–14,17,18,20,26,34,37,40

Hand Padding

All low- and high-energy padding conditions reduced linear-based impact dosage, including linear acceleration, GSI, neck force, and impact force. This finding was expected; padding has historically been designed to provide protection against linear dosage. However, when we examined rotational impact dosage results, and specifically for 2 of the real-world conditions (MMA glove–bare head and boxing glove–bare head), we found that some conditions reduced rotational impact dosage better than others. For example, the boxing glove–bare head condition always significantly reduced angular velocity, angular acceleration, angular momentum transfer, and neck moment compared with the unpadded control. In contrast, however, the MMA glove–bare head condition always significantly increased angular velocity and angular momentum transfer while having no effect on neck moment. The increased angular velocity and angular momentum were perhaps related to the fact that the MMA glove made contact for a greater time duration than did the boxing glove (0.0172 vs 0.0136 seconds in low-energy impacts and 0.0143 vs 0.0073 seconds in high-energy impacts). Therefore, the MMA glove induced greater angular velocity and momentum to the bare head by virtue of this greater duration of contact compared with the boxing glove–bare head condition.

The contact duration differences between the MMA–bare head and boxing glove–bare head scenarios may be due to the differences in padding compression,10,12,18,34,40 coefficient of friction,7 and the different glove masses in the different conditions. The only caveat was that contact duration appeared to have little or no effect on angular acceleration, as this parameter was reduced for both MMA glove–bare head and boxing glove–bare head low-energy conditions, and at high energy the boxing glove–headgear condition had the highest contact duration but lowest angular acceleration. Because angular acceleration has been routinely cited as a key rotational injury risk metric, our findings point to the need to consider additional rotational parameters like angular velocity, angular momentum transfer, and neck moment when quantifying head and neck impact dosage from boxing and MMA padding and impact conditions.

Although some real-world conditions significantly increased (high-energy boxing glove–bare head) or decreased (low-energy boxing glove–bare head) kinetic energy transfer, these differences were probably not very meaningful from an engineering or clinical perspective. The calculated injury risk functions GAMBIT, wPCS, and HIP were all significantly reduced for all conditions.

Advancing beyond empirical injury risk functions, the SIMon finite element brain injury model provided more specific insight into brain stretching, compression, and pressure. Hence, SIMon predicted a significantly lower risk of acute subdural hematoma (via the RMDM) and negligible risk of vacuum contusion (via the DDM) for the MMA glove–bare head, boxing glove–bare head, and boxing glove–headgear conditions. However, when comparing risk of diffuse axonal injury defined by a 5% brain strain (via the CSDM05), the SIMon-predicted CDSM05 values for the boxing glove–bare head and boxing glove–headgear conditions were significantly lower than the value for the unpadded control condition, while the predicted value for the MMA glove–bare head condition did not differ significantly from that of the unpadded control in the low-energy testing and was significantly higher than the control value in the high-energy testing. This was consistent with the increased rotational impact dosage associated with the MMA glove–bare head condition, which in turn was related to both greater rotational kinetic energy transmission and greater contact duration. SIMon generates injury risk results based on combined linear–rotational kinematic inputs. Hence, diffuse axonal injury (the etiology of which is thought to be, in part, related to rotational forces) may be expected to occur at a higher rate in MMA glove–bare head impacts than in similar boxing glove–bare head impacts. Moreover, it is important to note that the boxing glove–bare head condition had the best combined-parameter results, showing the largest reduction of all 3 real-world conditions for GAMBIT, wPCS, HIP, CSDM05, RMDM, and DDM. Finally, although significantly reduced compared with the unpadded control, the RMDM results for all 3 real-world conditions exceeded the theoretical injury threshold of 1.00 and indicated a heightened risk of acute subdural hematoma for the theoretical impact conditions we studied.

Head Padding

The existing literature on head padding for athletes has shown variable linear and rotational head and neck injury risk mitigation, dependent upon impact conditions.3,10,18,20,26,34,37,40 In particular, a recent study examining National Football League (NFL) football helmets37 found that of the 4 newer helmet models tested against an existing helmet model, none of the new helmets consistently reduced linear or rotational head and spine injury risk during a series of 10 real-world impact recreations. It should be noted that the NFL study conducted descriptive statistical analyses and could not be directly evaluated with the comparative statistical analysis from this study. Regardless, of the 3 real-world conditions (MMA glove–bare head, boxing glove–bare head, and boxing glove–boxing headgear) studied, the boxing glove–boxing headgear condition had the most meaningful reduction in most of the parameters quantified and should provide the best overall head and neck injury protection.

Study Vulnerabilities

A confounding factor associated with the methodology employed here was the variable mass of the impactor (simulated gloved hand) and ATD head. We conducted impacts at the higher range of human punch magnitude, while still being below impact magnitudes found in known concussive collisions.6,36,38 However, due to the changing mass of the impactor and ATD head, impact momentum and kinetic energy varied by as much as 7.5% and 7.8%, respectively. Therefore, the increased mass of the impactor or ATD head may have affected the postimpact head momentum and kinetic energy results. The significance of our results may have been different if impact momentum and/or energy were held constant between conditions. This, however, would have required the alteration of head and glove mass and/or impact velocity, which would have eliminated one source of variability by adding another. A further confounding variable was that the ATD head form's vinyl “skin” did not exactly reproduce human cranium-skin gliding, contact friction, or sweat. Hence, especially for the boxing glove–bare head and MMA glove–bare head conditions, the impact dosage outcomes may be different in a live person due to the differences between the human and ATD head form.

Conclusions

In our study, which replicated hook punches to the side of the head, results indicated that all padding conditions reduced linear impact dosage, including linear acceleration, GSI, neck force, and impact force. Our results suggest that head and neck impact dosages accumulate fastest in MMA and boxing conditions absent protective headgear. Additional injury risk parameters that included rotational kinetics and kinematics significantly decreased, significantly increased, or were unaffected depending on whether the impactor, head, or both, were padded. The SIMon finite element brain injury model indicated heightened theoretical risk of injurious brain strain injury for boxers or mixed martial artists regardless of padding used.

Of the 3 real-world conditions (MMA glove–bare head, boxing glove–bare head, and boxing glove–boxing headgear) studied, the boxing glove–boxing headgear condition had the most meaningful reduction in most of the parameters quantified and should provide the best overall head and neck injury protection for competitors. The MMA glove–bare head condition resulted in linear impact dosage that was superior to the boxing glove–bare head condition (that is, it was associated with a lower injury risk), but possibly due to increased contact duration with the ATD head, induced rotational impact dosage greater than the boxing glove–bare head condition (that is, it was associated with greater injury risk).

While extrapolating to the real world is difficult, our results point to the need to understand more about how single impact dosage or dosage accumulation over time may cause a heightened risk of acute and subacute injury as a function of the boxing and MMA protective padding used. Hence, the multivariate analysis presented here provides a methodology for studying this dosage accumulation in striking sports. Also, our results emphasize the need to examine protective athletic padding to minimize rotational impact dosage accumulation. Finally, this study clearly highlights the need to consider linear and rotational head and neck injury risk in developing impact test standards for next-generation protective padding.

Disclosure

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. They acknowledge assistance for the study from the National Institutes of Health Ruth L. Kirchstein T32 Training Grant AR050959, Cleveland Clinic Center for Spine Health, and Ohio Third Frontier. SEA, Ltd. provided use of the testing facility, impactor, instrumentation, data acquisition equipment, and Hybrid III ATD.

Author contributions to the study and manuscript preparation include the following. Conception and design: all authors. Acquisition of data: Bartsch, Miele, Morr. Analysis and interpretation of data: Bartsch, Morr, Prakash. Drafting the article: Bartsch, Morr, Prakash. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Bartsch. Statistical analysis: Bartsch, Morr, Prakash. Study supervision: all authors.

Appendix

This article contains an appendix that is available only in the online version of the article.

References

  • 1

    American Society for Testing and Materials: Standard Test Methods for Equipment and Procedures Used in Evaluating the Performance Characteristics of Protective Headgear. Designation: F1446-01a West Conshohocken, PAASTM International2002

  • 2

    Bandak FAZhang AXTannous REDiMasi FMasiello PEppinger R: SIMon: a simulated injury monitor; application to head injury assessment. National Highway Traffic Safety Administration (NHTSA) Website (http://www-nrd.nhtsa.dot.gov/pdf/esv/esv17/proceed/00222.pdf

  • 3

    Broglio SPJu YYBroglio MDSell TC: The efficacy of soccer headgear. J Athl Train 38:2202242003

  • 4

    Casson IRPellman EJViano DC: Concussion in the National Football League: an overview for neurologists. Phys Med Rehabil Clin N Am 20:195214x2009

  • 5

    Caswell SVDeivert RG: Lacrosse helmet designs and the effects of impact forces. J Athl Train 37:1641712002

  • 6

    Duma SMManoogian SJBussone WRBrolinson PGGoforth MWDonnenwerth JJ: Analysis of real-time head accelerations in collegiate football players. Clin J Sport Med 15:382005

  • 7

    Finan JDNightingale RWMyers BS: The influence of reduced friction on head injury metrics in helmeted head impacts. Traffic Inj Prev 9:4834882008

  • 8

    Fréchède BMcIntosh AS: Numerical reconstruction of real-life concussive football impacts. Med Sci Sports Exerc 41:3903982009

  • 9

    Gadd CW: Use of a weighted-impulse criterion for estimating injury hazard. Proceedings of the 10th Stapp Car Crash ConferenceNew YorkSociety of Automotive Engineers1966. 10:164174

  • 10

    Gilchrist AMills NJ: Protection of the side of the head. Accid Anal Prev 28:5255351996

  • 11

    Greenwald RMGwin JTChu JJCrisco JJ: Head impact severity measures for evaluating mild traumatic brain injury risk exposure. Neurosurgery 62:7897982008

  • 12

    Hrysomallis C: Impact energy attenuation of protective football headgear against a yielding surface. J Sci Med Sport 7:1561642004

  • 13

    Knouse CLGould TECaswell SVDeivert RG: Efficacy of rugby headgear in attenuating repetitive linear impact forces. J Athl Train 38:3303352003

  • 14

    Lewis LMNaunheim RStandeven JLauryssen CRichter CJeffords B: Do football helmets reduce acceleration of impact in blunt head injuries?. Acad Emerg Med 8:6046092001

  • 15

    Margulies SSThibault LE: A proposed tolerance criterion for diffuse axonal injury in man. J Biomech 25:9179231992

  • 16

    McElhaney JH: In search of head injury criteria. Stapp Car Crash J 49:vxvi2005

  • 17

    McIntosh AMcCrory PFinch CF: Performance enhanced headgear: a scientific approach to the development of protective headgear. Br J Sports Med 38:46492004

  • 18

    McIntosh ASMcCrory P: Impact energy attenuation performance of football headgear. Br J Sports Med 34:3373412000

  • 19

    National Operating Committee on Standards for Athletic Equipment (NOCSAE): Standard test method and equipment used in evaluating the performance characteristics of protective headgear/equipment. NOCSAE Website (http://www.nocsae.org/standards/pdfs/Standards%20'10/ND001-08m10-Drop%20Impact%20Test%20Method%20.pdf

  • 20

    Naunheim RSRyden AStandeven JGenin GLewis LThompson P: Does soccer headgear attenuate the impact when heading a soccer ball?. Acad Emerg Med 10:85902003

  • 21

    Newman JABeusenberg MCShewchenko NWithnall CFournier E: Verification of biomechanical methods employed in a comprehensive study of mild traumatic brain injury and the effectiveness of American football helmets. J Biomech 38:146914812005

  • 22

    Newman JAShewchenko NWelbourne E: A proposed new biomechanical head injury assessment function—the maximum power index. Snell Memorial Foundation Website (http://www.smf.org/docs/articles/hic/Newman_Max_Power_Index.pdf

  • 23

    Ommaya AKGoldsmith WThibault L: Biomechanics and neuropathology of adult and paediatric head injury. Br J Neurosurg 16:2202422002

  • 24

    Ommaya AKHirsch AE: Tolerances for cerebral concussion from head impact and whiplash in primates. J Biomech 4:13211971

  • 25

    Pellman EJViano DCTucker AMCasson IRWaeckerle JF: Concussion in professional football: reconstruction of game impacts and injuries. Neurosurgery 53:7998142003

  • 26

    Smith PKHamill J: The effect of punching glove type and skill level on momentum-transfer. J Hum Mov Stud 12:1531611986

  • 27

    Smith TABishop PJWells RP: Three dimensional analysis of linear and angular accelerations of the head experienced in boxing. Proceedings of the International Research Council on Biomechanics of ImpactVol 1:Bergish-Gladbach, GermanyIRCOBI19731989271286

  • 28

    Snell Memorial Foundation: Standard for protective headgear for use in non-motorized sports. Snell Memorial Foundation Website (http://www.smf.org/standards/n94/n94std

  • 29

    Society of Automotive Engineers: SAE Information Report. Sign Convention for Vehicle Crash Testing—SAE J1733 Warrendale, PASociety of Automotive Engineers1994

  • 30

    Society of Automotive Engineers: SAE Recommended Practice. Instrumentation for Impact Test—Part 1—Electronic Instrumentation—SAE J211/1 Warrendale, PASociety of Automotive Engineers1995

  • 31

    Stojsih SBoitano MWilhelm MBir C: A prospective study of punch biomechanics and cognitive function for amateur boxers. Br J Sports Med 44:7257302010

  • 32

    Takhounts EGEppinger RHCampbell JQTannous REPower EDShook LS: On the development of the SIMon finite element head model. Stapp Car Crash J 47:1071332003

  • 33

    Thibault LEGennarelli TA: Brain injury: an analysis of neural and neurovascular trauma in the non-human primate. Ann Proc Assoc Adv Automot Med 34:3373511990

  • 34

    Tierney RTHiggins MCaswell SVBrady JMcHardy KDriban JB: Sex differences in head acceleration during heading while wearing soccer headgear. J Athl Train 43:5785842008

  • 35

    Versace J: A review of the severity index. Proceedings of the 15th Stapp Car Crash ConferenceNew YorkSociety of Automotive Engineers1971. 771796

  • 36

    Viano DCCasson IRPellman EJBir CAZhang LSherman DC: Concussion in professional football: comparison with boxing head impacts—part 10. Neurosurgery 57:115411722005

  • 37

    Viano DCPellman EJWithnall CShewchenko N: Concussion in professional football: performance of newer helmets in reconstructed game impacts—part 13. Neurosurgery 59:5916062006

  • 38

    Walilko TJViano DCBir CA: Biomechanics of the head for Olympic boxer punches to the face. Br J Sports Med 39:7107192005

  • 39

    Withnall CShewchenko NGittens RDvorak J: Biomechanical investigation of head impacts in football. Br J Sports Med 39:Suppl 1i49i572005

  • 40

    Withnall CShewchenko NWonnacott MDvorak J: Effectiveness of headgear in football. Br J Sports Med 39:Suppl 1i40i482005

  • 41

    Zhang LYang KHKing AI: A proposed injury threshold for mild traumatic brain injury. J Biomech Eng 126:2262362004

Appendix

1) Impact Duration:

Impact duration was selected based on the length of the loading and unloading pulse after initial contact as based on impact force.

2) Neck Force:

article image

where
  • occX (t) = measured occipital force along x-axis

  • occY (t) = measured occipital force along y-axis

  • occZ (t) = measured occipital force along z-axis

3) Linear Momentum:

article image

where
  • mhead = 5.08kg

4) Impact Force:

article image

where
  • IX (t) = mhead CGX (t) − occX (t)

  • IY (t) = mhead CGY (t) − occY (t)

  • IZ (t) = mhead CGZ (t) − occZ (t)

5) Head Kinetic Energy:

article image

6) Gadd Severity Index (GSI):

article image

where
  • R (t) in g

  • [0: T] = essential impact duration, chosen to be 15 msec

7) Head Injury Criterion (HIC):

article image

where
  • R (t) in g

  • [t1 : t2] = time period, in msec, where HIC is maximized

8) Angular Velocity:

article image

where
  • ω̃X (t) = measured head angular velocity about x-axis

  • ω̃Y (t) = measured head angular velocity about y-axis

  • ω̃Z (t) = measured head angular velocity about z-axis

9) Angular Acceleration:

article image

where
  • α̃X (t) = measured head angular acceleration about x-axis

  • α̃Y (t) = measured head angular acceleration about y-axis

  • α̃Z (t) = measured head angular acceleration about z-axis

10) Upper Neck Moment:

article image

where
  • occX (t) = measured occipital moment about x-axis

  • occY (t) = measured occipital moment about y-axis

  • occZ (t) = measured occipital moment about z-axis

11) Angular Momentum:

article image

where
  • IX = head mass moment of inertia about x-axis = 0.0204kg-m2

  • IY = head mass moment of inertia about y-axis = 0.0211kg-m2

  • IZ = head mass moment of inertia about z-axis = 0.0143kg-m2

12) Generalized Acceleration Model for Brain Injury Threshold (GAMBIT):

article image

where
  • C = critical head linear acceleration 250g

  • α̃C = critical head angular acceleration 25,000rad/s2

13) Weighted Principle Component Score (wPCS):

article image

where
  • klat =1.0 for lateral impact

  • kGSI = 0.4718, GSIm = 25.83, GSIsd = 75.20

  • kHIC = 0.4720, HICm =17.65, HICsd = 51.95

  • kLIN = 0.4336, am = 26.24g, asd = 21.77g

  • kROT = 0.2164, α m = 1537rad / s2, αsd = 1432rad / s2

14) Head Impact Power (HIP):

article image

15) Cumulative Strain Damage Measure (CSDM05):

CSDM05 = % brain volume exceeding 5% principle strain as determined by SIMon Finite Element Model

16) Dilatational Damage Measure (DDM):

DDM = % brain volume experiencing negative pressure less than –101.4 kPa as determined by SIMon Finite Element Model

17) Relative Motion Damage Measure (RMDM):

article image

where
  • ε(t) = bridging vein strain as determined by SIMon Finite Element Model

  • εF(t, ε̇(t)) = bridging vein failure strain at given strain rate as determined by SIMon Finite Element Model

Article Information

Address correspondence to: Adam J. Bartsch, Ph.D., Cleveland Clinic Spine Research Laboratory, Luth2-C, 1730 West 25th Street, Cleveland, Ohio 44113. email: bartsca@ccf.org.

Please include this information when citing this paper: published online February 7, 2012; DOI: 10.3171/2011.12.JNS111478.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Photograph demonstrating the unpadded (control) impact condition.

  • View in gallery

    Photograph showing the bare pendulum–headgear condition.

  • View in gallery

    Photograph of the MMA glove–bare head condition.

  • View in gallery

    Photograph showing the boxing glove–bare head condition.

  • View in gallery

    Photograph demonstrating the boxing glove–headgear condition (high-energy trial only).

  • View in gallery

    Graphs illustrating the linear acceleration in the high-energy (upper) and low-energy (lower) trials.

  • View in gallery

    Graphs showing the angular velocity in the high-energy (upper) and low-energy (lower) trials.

  • View in gallery

    Graphs demonstrating the angular acceleration in the high-energy (upper) and low-energy (lower) trials.

  • View in gallery

    Graphs illustrating the impact force in the high-energy (upper) and low-energy (lower) trials.

  • View in gallery

    Representative frame from the SIMon computational simulation results displaying pressure isosurfaces within the brain from boxing glove–bare head impacts.

References

1

American Society for Testing and Materials: Standard Test Methods for Equipment and Procedures Used in Evaluating the Performance Characteristics of Protective Headgear. Designation: F1446-01a West Conshohocken, PAASTM International2002

2

Bandak FAZhang AXTannous REDiMasi FMasiello PEppinger R: SIMon: a simulated injury monitor; application to head injury assessment. National Highway Traffic Safety Administration (NHTSA) Website (http://www-nrd.nhtsa.dot.gov/pdf/esv/esv17/proceed/00222.pdf

3

Broglio SPJu YYBroglio MDSell TC: The efficacy of soccer headgear. J Athl Train 38:2202242003

4

Casson IRPellman EJViano DC: Concussion in the National Football League: an overview for neurologists. Phys Med Rehabil Clin N Am 20:195214x2009

5

Caswell SVDeivert RG: Lacrosse helmet designs and the effects of impact forces. J Athl Train 37:1641712002

6

Duma SMManoogian SJBussone WRBrolinson PGGoforth MWDonnenwerth JJ: Analysis of real-time head accelerations in collegiate football players. Clin J Sport Med 15:382005

7

Finan JDNightingale RWMyers BS: The influence of reduced friction on head injury metrics in helmeted head impacts. Traffic Inj Prev 9:4834882008

8

Fréchède BMcIntosh AS: Numerical reconstruction of real-life concussive football impacts. Med Sci Sports Exerc 41:3903982009

9

Gadd CW: Use of a weighted-impulse criterion for estimating injury hazard. Proceedings of the 10th Stapp Car Crash ConferenceNew YorkSociety of Automotive Engineers1966. 10:164174

10

Gilchrist AMills NJ: Protection of the side of the head. Accid Anal Prev 28:5255351996

11

Greenwald RMGwin JTChu JJCrisco JJ: Head impact severity measures for evaluating mild traumatic brain injury risk exposure. Neurosurgery 62:7897982008

12

Hrysomallis C: Impact energy attenuation of protective football headgear against a yielding surface. J Sci Med Sport 7:1561642004

13

Knouse CLGould TECaswell SVDeivert RG: Efficacy of rugby headgear in attenuating repetitive linear impact forces. J Athl Train 38:3303352003

14

Lewis LMNaunheim RStandeven JLauryssen CRichter CJeffords B: Do football helmets reduce acceleration of impact in blunt head injuries?. Acad Emerg Med 8:6046092001

15

Margulies SSThibault LE: A proposed tolerance criterion for diffuse axonal injury in man. J Biomech 25:9179231992

16

McElhaney JH: In search of head injury criteria. Stapp Car Crash J 49:vxvi2005

17

McIntosh AMcCrory PFinch CF: Performance enhanced headgear: a scientific approach to the development of protective headgear. Br J Sports Med 38:46492004

18

McIntosh ASMcCrory P: Impact energy attenuation performance of football headgear. Br J Sports Med 34:3373412000

19

National Operating Committee on Standards for Athletic Equipment (NOCSAE): Standard test method and equipment used in evaluating the performance characteristics of protective headgear/equipment. NOCSAE Website (http://www.nocsae.org/standards/pdfs/Standards%20'10/ND001-08m10-Drop%20Impact%20Test%20Method%20.pdf

20

Naunheim RSRyden AStandeven JGenin GLewis LThompson P: Does soccer headgear attenuate the impact when heading a soccer ball?. Acad Emerg Med 10:85902003

21

Newman JABeusenberg MCShewchenko NWithnall CFournier E: Verification of biomechanical methods employed in a comprehensive study of mild traumatic brain injury and the effectiveness of American football helmets. J Biomech 38:146914812005

22

Newman JAShewchenko NWelbourne E: A proposed new biomechanical head injury assessment function—the maximum power index. Snell Memorial Foundation Website (http://www.smf.org/docs/articles/hic/Newman_Max_Power_Index.pdf

23

Ommaya AKGoldsmith WThibault L: Biomechanics and neuropathology of adult and paediatric head injury. Br J Neurosurg 16:2202422002

24

Ommaya AKHirsch AE: Tolerances for cerebral concussion from head impact and whiplash in primates. J Biomech 4:13211971

25

Pellman EJViano DCTucker AMCasson IRWaeckerle JF: Concussion in professional football: reconstruction of game impacts and injuries. Neurosurgery 53:7998142003

26

Smith PKHamill J: The effect of punching glove type and skill level on momentum-transfer. J Hum Mov Stud 12:1531611986

27

Smith TABishop PJWells RP: Three dimensional analysis of linear and angular accelerations of the head experienced in boxing. Proceedings of the International Research Council on Biomechanics of ImpactVol 1:Bergish-Gladbach, GermanyIRCOBI19731989271286

28

Snell Memorial Foundation: Standard for protective headgear for use in non-motorized sports. Snell Memorial Foundation Website (http://www.smf.org/standards/n94/n94std

29

Society of Automotive Engineers: SAE Information Report. Sign Convention for Vehicle Crash Testing—SAE J1733 Warrendale, PASociety of Automotive Engineers1994

30

Society of Automotive Engineers: SAE Recommended Practice. Instrumentation for Impact Test—Part 1—Electronic Instrumentation—SAE J211/1 Warrendale, PASociety of Automotive Engineers1995

31

Stojsih SBoitano MWilhelm MBir C: A prospective study of punch biomechanics and cognitive function for amateur boxers. Br J Sports Med 44:7257302010

32

Takhounts EGEppinger RHCampbell JQTannous REPower EDShook LS: On the development of the SIMon finite element head model. Stapp Car Crash J 47:1071332003

33

Thibault LEGennarelli TA: Brain injury: an analysis of neural and neurovascular trauma in the non-human primate. Ann Proc Assoc Adv Automot Med 34:3373511990

34

Tierney RTHiggins MCaswell SVBrady JMcHardy KDriban JB: Sex differences in head acceleration during heading while wearing soccer headgear. J Athl Train 43:5785842008

35

Versace J: A review of the severity index. Proceedings of the 15th Stapp Car Crash ConferenceNew YorkSociety of Automotive Engineers1971. 771796

36

Viano DCCasson IRPellman EJBir CAZhang LSherman DC: Concussion in professional football: comparison with boxing head impacts—part 10. Neurosurgery 57:115411722005

37

Viano DCPellman EJWithnall CShewchenko N: Concussion in professional football: performance of newer helmets in reconstructed game impacts—part 13. Neurosurgery 59:5916062006

38

Walilko TJViano DCBir CA: Biomechanics of the head for Olympic boxer punches to the face. Br J Sports Med 39:7107192005

39

Withnall CShewchenko NGittens RDvorak J: Biomechanical investigation of head impacts in football. Br J Sports Med 39:Suppl 1i49i572005

40

Withnall CShewchenko NWonnacott MDvorak J: Effectiveness of headgear in football. Br J Sports Med 39:Suppl 1i40i482005

41

Zhang LYang KHKing AI: A proposed injury threshold for mild traumatic brain injury. J Biomech Eng 126:2262362004

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