Differences in the performance of wood and metal baseball bats, measured as a function of batted ball speed, were quantified in a batting cage study. Two wood and five metal baseball bat models were studied with 19 players of various levels of experience ranging from high school to professional. Batted ball speeds from 538 hits were computed from high-speed 3-D ball position data collected with a commercially available system. In general, metal bats had significantly higher batted ball speeds than wood bats. Of the five metal bat models studied, one outperformed all other models and one bat was most similar to wood bats. The average difference in batted ball speed between wood bats and the highest performing metal bat was approximately 9 mph. Maximum batted ball speeds of 101 and 106 mph were measured for wood and metal bats, respectively. Increased skill level significantly increased the maximum batted ball speeds generated independent of bat model. Players of all experience levels were able to generate batted ball speeds in excess of 100 mph. While the results of this study are limited to the specific bats tested, this is the first study to measure and report differences in batted ball speeds among wood and metal bats.
Richard M. Greenwald, Lori H. Penna and Joseph J. Crisco
Shonn P. Hendee, Richard M. Greenwald and Joseph J. Crisco
In this study we investigated the compressive quasi-static mechanical properties and dynamic impact behavior of baseballs. Our purpose was to determine if static testing could be used to describe dynamic ball impact properties, and to compare static and dynamic properties between traditional and modified baseballs. Average stiffness and energy loss from 19 ball models were calculated from quasi-static compression data. Dynamic impact variables were determined from force–time profiles of balls impacted into a flat stationary target at velocities from 13.4 to 40.2 m/s. Peak force increased linearly with increasing ball model stiffness. Impulse of impact increased linearly with ball mass. Coefficient of restitution (COR) decreased with increasing velocity in all balls tested, although the rate of decrease varied among the different ball models. Neither quasi-static energy loss nor hysteresis was useful in predicting dynamic energy loss (COR2). The results between traditional and modified balls varied widely in both static and dynamic tests, which is related to the large differences in mass and stiffness between the two groups. These results indicate that static parameters can be useful in predicting some dynamic impact variables, potentially reducing the complexity of testing. However, some variables, such as ball COR, could not be predicted with the static tests performed in this study.
Jonathan G. Beckwith, Jeffrey J. Chu and Richard M. Greenwald
Although the epidemiology and mechanics of concussion in sports have been investigated for many years, the biomechanical factors that contribute to mild traumatic brain injury remain unclear because of the difficulties in measuring impact events in the field. The purpose of this study was to validate an instrumented boxing headgear (IBH) that can be used to measure impact severity and location during play. The instrumented boxing headgear data were processed to determine linear and rotational acceleration at the head center of gravity, impact location, and impact severity metrics, such as the Head Injury Criterion (HIC) and Gadd Severity Index (GSI). The instrumented boxing headgear was fitted to a Hybrid III (HIII) head form and impacted with a weighted pendulum to characterize accuracy and repeatability. Fifty-six impacts over 3 speeds and 5 locations were used to simulate blows most commonly observed in boxing. A high correlation between the HIII and instrumented boxing headgear was established for peak linear and rotational acceleration (r 2 = 0.91), HIC (r 2 = 0.88), and GSI (r 2 = 0.89). Mean location error was 9.7 ± 5.2°. Based on this study, the IBH is a valid system for measuring head acceleration and impact location that can be integrated into training and competition.
Matthew D. Mecham, Richard M. Greenwald, James G. Macintyre and Stephen C. Johnson
A field study was performed using freestyle aerial ski jumpers to determine the incidence of head impact (slapback) and to record head acceleration data during slapback episodes for the 1994–1995 and 1995–1996 winter seasons. A total of 382 slapbacks were recorded from 2,352 jumps for an observed slapback incidence of 16.2%. Head acceleration data were recorded for 5 slapback events. Maximum head acceleration magnitudes for the 5 impacts ranged from 27 to 92 gs and impact durations ranged from 12 to 96 μsec. Standard severity indices including the Gadd Severity Index and Head Injury Criteria were calculated from the resultant acceleration signal and ranged from 57 to 223, and 21 to 159, respectively, which are considered low in terms of life threatening injury levels.
Steven Rowson, Jonathan G. Beckwith, Jeffrey J. Chu, Daniel S. Leonard, Richard M. Greenwald and Stefan M. Duma
The high incidence rate of concussions in football provides a unique opportunity to collect biomechanical data to characterize mild traumatic brain injury. The goal of this study was to validate a six degree of freedom (6DOF) measurement device with 12 single-axis accelerometers that uses a novel algorithm to compute linear and angular head accelerations for each axis of the head. The 6DOF device can be integrated into existing football helmets and is capable of wireless data transmission. A football helmet equipped with the 6DOF device was fitted to a Hybrid III head instrumented with a 9 accelerometer array. The helmet was impacted using a pneumatic linear impactor. Hybrid III head accelerations were compared with that of the 6DOF device. For all impacts, peak Hybrid III head accelerations ranged from 24 g to 176 g and 1,506 rad/s2 to 14,431 rad/s2. Average errors for peak linear and angular head acceleration were 1% ± 18% and 3% ± 24%, respectively. The average RMS error of the temporal response for each impact was 12.5 g and 907 rad/s2.
Srinidhi Bellamkonda, Samantha J. Woodward, Eamon Campolettano, Ryan Gellner, Mireille E. Kelley, Derek A. Jones, Amaris Genemaras, Jonathan G. Beckwith, Richard M. Greenwald, Arthur C. Maerlender, Steven Rowson, Stefan M. Duma, Jillian E. Urban, Joel D. Stitzel and Joseph J. Crisco
This study aimed to compare head impact exposures between practices and games in football players ages 9 to 14 years, who account for approximately 70% of all football players in the United States. Over a period of 2 seasons, 136 players were enrolled from 3 youth programs, and 49,847 head impacts were recorded from 345 practices and 137 games. During the study, individual players sustained a median of 211 impacts per season, with a maximum of 1226 impacts. Players sustained 50th (95th) percentile peak linear acceleration of 18.3 (46.9) g, peak rotational acceleration of 1305.4 (3316.6) rad·s−2, and Head Impact Technology Severity Profile of 13.7 (24.3), respectively. Overall, players with a higher frequency of head impacts at practices recorded a higher frequency of head impacts at games (P < .001, r 2 = .52), and players who sustained a greater average magnitude of head impacts during practice also recorded a greater average magnitude of head impacts during games (P < .001). The youth football head impact data quantified in this study provide valuable insight into the player exposure profile, which should serve as a key baseline in efforts to reduce injury.
Joseph J. Crisco, Bethany J. Wilcox, Jason T. Machan, Thomas W. McAllister, Ann-Christine Duhaime, Stefan M. Duma, Steven Rowson, Jonathan G. Beckwith, Jeffrey J. Chu and Richard M. Greenwald
The purpose of this study was to quantify the severity of head impacts sustained by individual collegiate football players and to investigate differences between impacts sustained during practice and game sessions, as well as by player position and impact location. Head impacts (N = 184,358) were analyzed for 254 collegiate players at three collegiate institutions. In practice, the 50th and 95th percentile values for individual players were 20.0 g and 49.5 g for peak linear acceleration, 1187 rad/s2 and 3147 rad/s2 for peak rotational acceleration, and 13.4 and 29.9 for HITsp, respectively. Only the 95th percentile HITsp increased significantly in games compared with practices (8.4%, p = .0002). Player position and impact location were the largest factors associated with differences in head impacts. Running backs consistently sustained the greatest impact magnitudes. Peak linear accelerations were greatest for impacts to the top of the helmet, whereas rotational accelerations were greatest for impacts to the front and back. The findings of this study provide essential data for future investigations that aim to establish the correlations between head impact exposure, acute brain injury, and long-term cognitive deficits.