The incidence and severity of impact injuries in baseball is a substantial problem in sports medicine. Batted-ball injuries to pitchers from balls are well-documented phenomena in junior and collegiate baseball (5) and the professional game (7). Decreasing BEV may reduce the frequency and severity of such injuries. To develop meaningful performance regulations for bats and balls, the effect of equipment design on BEV must be rigorously quantified. This is the first study to evaluate the performance of wood and metal baseball bats in terms of the maximum risk of injury to the pitcher from balls hit by each bat directly toward him. Using a model driven by bat kinematics from high-performance hitters and experimentally determined ball time-dependent properties, it was shown both wood and metal bats can produce BEV that exceeds the reaction time of pitchers when compared with the data of Cassidy and Burton (8). Impact between the handle-weighted metal bat and the high stiffness ball (Model A) recorded the highest BEV (61.5 m·s−1), with 0.282 s available for evasive action (Fig. 4). For impact from the wood bat with ball Model B, 0.377 s was available for the pitcher to react to a ball hit directly at him, which was still within the 0.400-s “danger window” for a pitcher to be struck by the ball (8). Reduction in the instantaneous shear (G0) and relaxation (G∞) modulii of the baseballs increased the time available for evasive action by the pitcher by approximately 10%.
The immediate implications for this research are in the risk and severity of injury faced by unprotected pitchers from balls hit directly toward them. Our results suggest in the worst case (MA), the ball will have a velocity of 55.4 m·s−1 when it reaches the pitcher 16.46 m away. In the best case (WB), the ball velocity at the pitcher will be 41.4 m·s−1. Although the biomechanics of impact injuries are beyond the scope of this paper, Heald and Pass (13) and Viano et al. (28) showed skull fracture in cadaver heads occurred at 26.2 m·s−1 for impacts with a professional standard baseball. Approximately half of the fatalities to baseball pitchers are caused by impact to the head (27). Pasternack et al. (23) indicated 86% of head and facial injuries in Little League players are caused by ball impact, of which 85% occur to defensive players. Chest impact by the ball comprised 35% of 23 deaths among pitchers between 1973 and 1983 (27). The rate of deaths from chest impact to nonprofessional baseball pitchers increased from 2.1 per year in 1973–1980 to 3.3 per year in 1986–1990 (29). While these figures may reflect increased participation, the use of increasingly high-performance metal bats and stiffer baseballs may also be a contributing factor. Link et al. (15) indicated, in a swine model, the likelihood of ventricular fibrillation was related to the timing of the blow within the cardiac cycle, not the velocity or force of the impact. The results of the present study highlight the danger faced by the unprotected pitcher. The BEV values obtained from this mathematical analysis are substantially higher than those suggested by Owings et al. (22) as the maximum which could be avoided by Little League players. Hence, increasing the available movement time by modification of equipment or playing rules is necessary to reduce the incidence of impact injuries to pitchers.
Pitcher fielding technique, and the size and strength of hitters, are two factors not considered in this study that may be related to the incidence of pitcher injuries. The relationship of the throwing and fielding technique used by pitchers compared with movement time needed to avoid being struck by the ball remains to be investigated. The power of modern professional hitters is demonstrated by Major League performances in the week of August 13, 2002, in which four players hit three home runs each in a game. Similarly, in collegiate baseball, the average number of home runs per game has doubled from 0.45 to 0.9 since 1972 (1). Reduction in ball-impact injuries requires a wide-ranging response and may include the use of safety equipment, separation of players by age, size, and skill level, and enforcement of existing rules regarding the distance between batters and fielders in practice and in games. This study was limited to assessment of the impact response of bats and balls, and the results are specific to the equipment models tested. However, the results have important consequences for the design and regulation of this equipment. The results obtained in this research indicate both bat design (moment of inertia) and ball behavior (shear and relaxation properties) influence BEV.
Metal bats were introduced into baseball in 1972 to address rising costs associated with broken wood bats. With 19 million participants each year in the United States (27), reversion to the exclusive use of wood bats is not an economically viable strategy to reduce the likelihood of ball-impact injuries to pitchers. Our findings lend support to the 1999 proposal by the NCAA Baseball Research Panel to instead regulate the swing moment of metal bats (10). Bat kinematics at impact have been shown to be a combination of translational and rotational motion (18). Resistance to this motion is affected both by bat mass and the distribution of that mass with respect to axis about which it is rotating. The results of this research indicate bat moment of inertia is an important factor in bat preimpact linear velocity and 3-D orientation and hence both resultant BEV and the distribution of the BEV among horizontal, lateral, and vertical components. Our results suggest handle-weighting of bats results in higher BEV. The higher moment of inertia of the wood bat resulted in lower preimpact linear velocity and a more oblique bat–ball impact. The energy lost to lateral motion was an important factor in the lower BEV recorded from this bat. The greater barrel lag at impact for the wood bat may point toward a potential design-control method for BEV. Similarly, metal bat swing moment may be controlled through modifications such as adjustments in barrel wall thickness and changes in handle diameter and knob weight.
Although it has been suggested having external automatic defibrillators and medical personnel present at youth games to treat impact injuries (29), prevention of such injuries may be more efficacious. The dynamic material behavior of the baseball is complex and was previously not well understood. The current study constitutes the first research to measure the elastic and time-dependent properties of baseballs under large-deformation conditions. The results of this analysis indicate variation in the time-dependent properties of the ball is a viable method for reducing BEV, which in turn may reduce the frequency and perhaps the severity of batted-ball injuries. The performance characteristics of softer balls have not previously been subject to rigorous study, and the results of the current study point to an avenue for improving the safety of infielders while retaining the intrinsic character of the game.
Conflict of Interest: While acknowledging the support of the above-listed organizations who supplied two baseball bats and 70 baseballs for the purposes of this research, we hereby state we have no further or ongoing professional relationship with these companies or manufacturers from which they might derive benefit from the results of the present study. The results of the present study do not constitute endorsement of the product by the authors or ACSM.
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