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softball injuries

Blunt Chest Impacts:
Assessing the Relative Risk of Fatal Cardiac Injury from
Various Baseballs

David H. Janda, MD, Cynthia A. Bir,, MS, RN, David C. Viano, PhD, and Stephen J. Cassaria, MSE

To compare various soft-core baseballs for their ability to reduce the risk of fatal chest-impact injury.

This study used a three-rib biomechanical surrogate to quantitatively analyze chest impacts from nine soft-core baseballs and one standard baseball, which served as the control. Impacts were achieved with an air cannon system, with the velocity of impact being 40, 50, and 60 mph.

Materials and Methods:
The deflection of the three-rib structure at the sternum was measured and used to calculate the viscous criterion, which correlates with risk of chest-impact injury.

Measurements and Main Results:
Analysis showed that baseballs with lighter mass had a significantly lower viscous criterion (p < 0.05). Those with a similar mass had no change in the viscous criterion, and the heaviest soft-core baseball had a significantly higher viscous criterion at an impact velocity of 60 mph.

The results of this study indicate that soft-core baseballs may not differ from a standard baseball with regard to the risk of fatal chest-impact injury while playing baseball. Other techniques, such as preventive coaching, need to be implemented when trying to improve baseball safety.

Key Words:
Baseball, Injury prevention, Commotio cordis, Cardiac arrhythmia, Viscous criterion.

It has been estimated that more than 19 million Children are involved in youth baseball in the United States.1 It has also been estimated that softball and baseball lead to more injuries necessitating emergency room visits in the United States than any other sport. Between 1983 and 1994, more than 4.8 million injuries secondary to softball and baseball were documented through selected emergency rooms throughout the United States by the Consumer Product Safety Commission.2 In 1981, the Consumer Product Safety Commission concluded that more fatalities occur in the 5- to 14-year age group as a result of baseball than any other sport. There were 88 deaths related to baseball in this age group between 1973 and 1995: 68 were caused by impacts with the ball, 13 were caused by impacts with the bat, and 7 were from another cause or were of unknown cause. Baseball impacts to the chest caused 38 of the 68 deaths attributable to the ball, whereas impacts to the head and other regions accounted for the other 30 deaths.2 These data translate into one death in youth baseball for every 4.75 million participants.

In 1995, Maron et al.3 reported on 25 individuals, aged 3 to 19 years, who died secondary to blunt chest impacts while participating in a variety of sports. The majority of these cases (18 of 25) occurred while playing baseball or softball. Of the 25 deaths, 19 had cardiopulmonary resuscitation initiated within about 3 minutes of their collapse, and 28% of the victims were wearing some sort of chest protector. Autopsies were performed on 22 of the 25 subjects. All were found to be free from cardiac structural abnormalities, with only small contusions evident on the left side of the chest in 12 of the victims.

    Episodes of sudden death without structural cardiac damage in individuals participating in sports have been referred to as commotio cordis.4 Commotio cordis has been hypothesized to occur as a result of apnea, vasovagal reflex, or ventricular arrhythmia: The occurrence of blunt chest impacts leading to ventricular arrhythmia has been supported elsewhere. Liedtke et al.5 demonstrated that a blunt trauma caused a redistribution of the blood flow in the small vessels of the heart. It was thought that this disruption in the perfusion of the myocardium was the cause of hemodynamic and electrophysiologic changes within the heart. It is these electrophysiologic changes, or arrhythmia, that appear to be the foundation of commotio cordis, an injury often not associated with serious, gross myocardial damage. In animal experiments, Viano et al.6 reported the presence of ventricular fibrillation (VF) in 7 of 16 chest impacts with baseballs. These impacts, occurring at a velocity of 95 mph (42.8 ni/s), consistently produced the fatal arrhythmia and traumatic apnea. In most of the reported clinical cases of commotio cordis, however, the velocity of impact was thought to be between 30 and 50 mph.3 The velocity of impact, therefore, is not the sole factor for blunt-impact fatalities.

    In an effort to determine other factors associated with commotio cordis and traumatic cardiac arrest, the timing of the chest impact has been studied by researchers.7'8 Cooper et al.7 investigated the biomechanics of nonpenetrating chest impacts in an animal model. Several tests were performed, including electrocardiography of the heart. It was demonstrated that VF was the most serious arrhythmia produced by these impacts. Upon analysis of the results, the T wave of the electrocardiogram was identified as a vulnerable period of the cardiac cycle. Impacts occurring at this time appear to initiate VF. In six impacts resulting in acute VF, four occurred during the T wave. This finding was corroborated by Kroell et al.8 who found that five of eight impacts resulting in immediate VF occurred during the T wave. These findings seem consistent with the fact that this period in the cardiac cycle represents a time when cardiac cells may he repolarized, depolarized, or partially repolarized. Electrically, therefore, the heart is more vulnerable.8

    Along with functional injuries associated with blunt thoracic impact, there exist structural injuries, such as cardiac contusion and rupture. In an effort to evaluate all parameters of cardiac injury, Icroell et al.8 conducted a series of experiments. The studies investigated the interrelationship between velocity of impact, compression of the chest, and injury in an animal surrogate. The responses evaluated included Abbreviated Injury Scale score, presence of arrhythmia including ventricular fibrillation, number of rib fractures, heart rupture, and the evaluation of biomechanical responses. The biomechanical responses included the impact velocity, maximum chest compression, and maximum viscous response.

  The viscous criterion (VC) is a time-dependent product of the velocity of the chest deformation (V) and the amount of compression (C).9 The chest compression is defined as the displacement of the chest in relationship to the spine normalized by the initial thickness of the thorax. This criterion is thus dependent not only on the amount of compression but also on the rate at which the compression occurs. The viscous response is related to the energy absorbed by the body, including the heart, during the rapid phase of chest compression.

   The ability to determine the viscous response or VC of an impact on a large scale becomes problematic. Case studies of human fatalities leave the researcher with limited postmortem data. Although an animal surrogate could serve as an in vivo model of the event, there is a lack of an ability to complete a large number of tests. Logically, a biomechanical surrogate validated against an animal model would allow for reproducible data to be acquired and analyzed.

   It is the purpose of this study to use an experimental model, the three-rib system, to evaluate the effectiveness of various soft-core and lighter-mass baseballs in their ability to reduce the magnitude of chest impact and risk of fatality. This study was designed to evaluate several soft-core baseballs at the velocities likely to be seen during little league play: 40, 50, and 60 mph. The standard baseball served as the control for this study.



Nine soft-core baseballs were tested as part of the experimental group in the present study. The 'Official League" baseball manufactured by Rawlings served as the control (Fig. 1). The mass of each ball was determined before testing. Table 1 lists the types of balls tested and the respective mass of each.

fig 1.jpg (18988 bytes)Figure 1. click image to expand

Nine soft-core baseballs were tested, with the standard baseball serving as the control
Click on Image to enlarge

Table 1.jpg (22277 bytes) Table 1. click image to expand

Three-Rib Structure

Chest-impact measurements were obtained using a three-rib chest structure that was constructed with the rib subunits of the BIOSID test dummy. The BIOSID is a biomechanical surrogate that has been extensively tested and was developed for purposes of determining biomechanical responses in blunt-impact scenarios. The entire system was not used for this study, however, because it is a lateral-impact system suitable for high-velocity, blunt-impact studies. Only the rib components of the BIOSID were used in the development of the three-rib system.

The three-rib system was developed because of the need for a portable, low-cost surrogate that has biofidelity to human chest-impact responses. It was considered ideal for the chest impacts that were performed for this study because the rib structures were continuous and therefore provided an adequate loading surface for the concentrated impacts of a baseball. This system is similar to the Hybrid III in its ability to measure chest-deflection data from which VC can he calculated.

The basic structure involved three thorax ribs mounted to a spine box opposite the impact side (Fig. 2). Dampening material on the inside of the rib provided for viscous bending resistance and allowed for the dissipation of energy. Nylon supports were mounted to the sides of the spine box to prohibit the upward and downward motion of the ribs. A 15.5 cm 7 23 cm urethane bib tied the three ribs together on the impact side. The urethane was further covered with padding made of Ensolite (Robatex, Bedford, Va) approximately 2.5 cm thick to simulate overlying skin and subcutaneous tissue.

Fig 2.jpg (22067 bytes) Figure 2 - click image to expand

    To measure the amount of chest deflection, a position transducer was mounted to the interior of the ribs in the anterior-posterior position. This transducer was connected directly behind the urethane bib in the sternal region. The base of the transducer was mounted within the spine box. This arrangement allowed for the total amount of chest displacement to be measured.

    The linearity of the position transducer was verified statically over a range of 50 mm and dynamically for velocities up to 10 m/s. Differentiation of the rib displacement curve verified that this velocity was not exceeded during the testing. Calibration tests with the three-rib system demonstrated an average 6.8% coefficient of variation in VC and 3.4% in chest deflection for 11 tests with 2.3% coefficient of variation in test speeds.

    The chest structure was placed on a free-moving sled to allow for horizontal movement with each impact, simulating whole-body motion in an impact. A pressurized air cannon, which discharged the baseballs, was placed approximately 39 inches in front of the chest structure. The projectile velocities were 40,50, and 60mph (17.9, 22.4, and 26.8 mis). The sled was repositioned to the same starting point after each impact, and the amount of displacement of the entire system was recorded. Velocities of the baseballs were recorded with an Oehler Research, Inc. (Austin, Tex), model 35P chronograph.

Analysis and Interpretation of Biomechanical Responses

The baseballs impacted anteroposterior to the midpoint of the sternal and thoracic area. As described above, the amount of deflection in the chest was measured with a linear chest-deflection transducer located at the center of the impact region. A Texas Micro Systems (Santa Barbara, Calif) 486 computer with a RC Electronics (Houston, Tex) A-to-D conversion board and software served as the data-acquisition system used to record these responses.

    The variables collected included velocity of ball at impact, total displacement of the chest, and linear displacement of the entire three-rib/sled unit. The velocity of the ball at impact dictates, along with the ball mass, the amount of energy going into the system. The chest displacement is indicative of the amount of impact energy absorbed by the chest. In addition, it allows for calculation of the viscous criterion to which cardiac injury can be correlated. The distance that the entire three-rib/sled unit traveled on the rail system is indicative of the amount of energy being absorbed by the entire unit. It represents the amount of energy transferred into the system minus the amount of energy absorbed by the thorax structure and rebound of the ball.

    In 1986, Kroell et al.8 validated the viscous criterion as the best predictor of the probability of heart rupture and thoracic injuries with Abbreviated Injury Scale scores > 3. Further analysis by Viano and Lau 10 resulted in the determination that the VC was the best indicator of soft-tissue injuries for many body regions when the velocity of deformation was in the 3 to 30 mis range. The difficulty of determining how VC relates to commotio cordis exists because of the lack of previous analysis and the enigma surrounding the event of commotio cordis itself.

    To determine the trends that are prevalent within the data, the average VC for each of the baseballs at each of the velocities was normalized. The standard ball at 60-mph (26.8 m/s) served as the normalization factor for this process. The standard ball was chosen because it served as the control for the study, and the velocity of 60-mph (26.8 rn/s) was chosen because it provides the most severe impact.

    Each ball was 'thrown" at the three-rib structure a total of 10 times at each velocity. The balls were randomly sampled without replacement until all 10 balls were tested, at which time the process was repeated with the same set of 10 balls. A coefficient of variation was calculated for each group within the analysis of the data to ensure repeatability.

Statistical Methods

Differences in the data were statistically evaluated using an analysis of variance. Further analysis involved a Bonferroni (Dunn) t test when the analysis of variance was significant (p < 0.05). The probability of injury was determined by logistical analysis using SAS software (SAS, Inc., Cary, NC). The values of X2, R, and p are reported, as well as the statistical parameters for the sigmoidal model for injury risk.



Viscous Response

    The results of the testing were stratified according to the three different velocities and the variables of VC, sternal displacement, and sled displacement. The trends in the data can be demonstrated by normalizing the data. The VC values were used when evaluating the trends because they have been shown to be the greatest indicator of injury.9 As stated above, the normalizing factor was the standard baseball response at 60-mph (26.8 rn/s). As is evident in our graphic analysis (Fig.3), there is generally an increase in the VC values as the velocity increases.

fig 3.jpg (26622 bytes)Figure 3 - click image to expand

    One ball, the Incrediball, had a significantly lower VC value for all three velocities (p < 0.05). This was also the lightest baseball tested. Five of the other balls (RIFI, SafeT, Incrediball Pro, ADStarr5, and Flexiball) all had a significant reduction in VC values for at least one of the tested velocities. There was one ball that produced a significantly higher VC than the standard to the p < 0.05 level, the ADStarr10 at 60 mph (26.8 rn/s). Table 2 shows the results of all the baseballs stratified at each velocity.

table 2.jpg (33337 bytes)Table 2 - click image to expand

Sled Displacement

    The results of the entire sled displacement are presented in Figure 4. These results are indicative of how the whole body would respond to an impact with a given ball. It would seem logical that whole-body motion would be more advantageous than deflection within the thorax from an injury standpoint. What this displacement means from an injury standpoint is inconclusive, however, because the coefficient of friction of the sled is unknown. It should be noted that the baseballs of lower mass will provide a lower-energy input at a greater velocity; therefore, less energy is available to move the sled or cause thoracic deformation. Further testing will be needed to determine how the sled displacement relates to other types of injury mechanisms.

Fig 4.jpg (29434 bytes)Figure 4 - click image to expand


    This study was prompted by the need to address fatalities related to blunt chest impact that is occurring on the baseball fields of the youth population. The use of a biomechanical surrogate in a laboratory setting provided values for an injury criterion, namely, the viscous criterion. The VC was developed to analyze chest-impact data by considering both the variable of compression and the velocity of compression. This criterion has been used extensively in the automotive industry, where blunt thoracic trauma also poses a safety concern.

    The results of this study indicate that the use of soft-core baseballs does not necessarily protect the player from the possibility of chest-impact injury to a significant level compared with the standard baseball. In fact, one of the soft-core baseballs actually generated a significantly higher VC than the standard baseball: the ADStarr10 at 60-mph (26.8 m/s). Only one baseball demonstrated a significant reduction in the VC at all three velocities: the Incrediball. This baseball also had the lowest mass of those tested. Several baseballs had a significantly lower VC at 60 mph (26.8 m/s): RIFI, SafeT, Incrediball, Incrediball Pro, ADStarr5, and Flexiball.

    In addition to the results reported above, at least one death has occurred on the field while a soft-core baseball was being used.3 The occurrence of chest-impact injury is therefore possible even with the soft-core baseballs. In a recent study, the risk of injury with soft-core baseballs was 1 injury per 6,855 player-hours, compared with 1 injury per 7,889 players-hours with standard baseballs.11 Even though there was a decrease in the VC values of impacts with some of the soft-core baseballs, the timing of the impact remains a crucial, uncontrollable variable in actual baseball impacts.7 It is impossible, therefore, to provide players with a guarantee that a ball will prevent all injuries and fatalities.

    The problems that exist when using a soft-core baseball need to be addressed. The first factor to consider is that the majority of players using the soft-core baseball are among the youth population. This is a population in which chest-impact injury is more prevalent because of the increase in compliance of the thorax structure in comparison with the adult. Second, the marketing and use of a potentially safer ball can give a false sense of security. Children may be more likely to take a greater risk in fielding the ball or not moving away from a wild pitch if they believe that there is a decreased risk of injury.

    Unfortunately, the production of a baseball that will significantly reduce the rate of injuries may not be possible when considering the chest-impact scenario. Adequate coaching techniques may be more likely to address these concerns. Teaching a child how to "get out of the way" or to turn his or her chest away from a wild pitch may be more effective in reducing the rate of injuries than any other technique. Before players take the field, they should realize that protective equipment will not prevent all injuries or fatalities and that other preventive measures should be taken.

    Based on the results of this study, further analysis and testing regarding the biomechanics of commotio cordis is encouraged. When all other factors are equal, however, the presented test method and the calculation of VC provides a means of determining the risk of injury related to blunt chest impacts. Based on this test method, only the baseballs with the lower VC values would have a lower risk of injury. Those baseballs with VC values that are not significantly lower than those of the controls should not be considered to be safer than the standard baseballs. Furthermore, the efficacy of educational coaching regarding injuries related to baseball and softball should be assessed.


The authors express their appreciation to Mr. Brian Czach for his assistance with the development of the three-rib structure. Thanks must also go to Angela Cheney for her efforts within the testing laboratory. And finally, we thank Dr. Anthony Schork for his assistance with the statistical analysis.


1. Presented at the National Youth Sports Coaches Association, National Summit for Baseball Safety; September 5-7,1991; Orlando, Fla.
2. Product Summrn Reports, National Electronic injury Surveillance System, June 1983 through 1995. Washington,DC:Consumer Product Safety Commission; 1996.
3. Maron BJ, Poliac LC, Kaplan JA, et al. Blunt impact to the chest leading to sudden death from cardiac arrest during sports activities. N Engi J Med. 1995;333:337.
4, Abrunzo TJ. Commotio cordis: the single, most common cause of traumatic death in youth baseball. Am J Dis Child.1991;145:1279.
5. Liedtke AJ, Allen RP, Nellis SH. Effects of blunt cardiac trauma on coronary vasomotion, perfusion, myocardial mechanics, and metabolism. J Trauma. 1980;20:777.
6. Viano DC, Andrzejak DV, Polley TZ, et al. Mechanism of fatal chest injury by baseball impact in children:development of an experimental model. Clin J Sport MeJ 1992;2: 166.
7. Cooper Ci, Pearce BP, Stainer MC, et at. The biomechanical response of the thorax to nonpenetrating impact with particular reference to cardiac injuries. J Trauma. 1982;22:994.
8. Kroell CK, Allen S, Warner CY, et al. Interrelationship of velocity and chest compression in blunt thoracic impact to swine II. In: Proceedings of the 30th Stapp Car Crash Conference.  Warrendale, Pa: Society of Automotive Engineers; 1986:99. SAE technical paper 861881.
9. Viano DC, Lau IV. A viscous tolerance criterion for soft tissue injury assessment. J Biomech. 1988;2l :387.
10. Viano DC, Lau IV. Thoracic impact: a viscous tolerance criterion. In: Tenth International Conference on Experimental Safety Vehicles. Oxford, England: 1985:104-114.
11. Pastemack iS, Vecnema KR, Callahan CM. Baseball injuries: a little league survey. Pediatrics. 1996;98:445.

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