Softball bat inertial considerations and their effects on female softball swing mechanics and estimated bat performance

This paper discusses the role of the inertial properties in the design and selection of the softball bat, and their interrelated effects on female softball swing mechanics and bat performance. The study was performed using 14 collegiate subjects whose swings were analyzed via a computer model, which included methods for estimating post-impact ball velocity. The model was driven kinematically by subject swing recordings using two different trial bats with markedly different inertial properties. Using this method, the following information was determined: subjects altered their linear kinetic inputs while applying consistent angular kinetic inputs to maintain nearly consistent trajectories; subjects compensated for increased bat inertia by modification of the bat instantaneous center-of-rotation trajectory ( ICR); and swing trajectory influenced the bat’s inertial feel, actual, and ideal impact locations, and batted-ball velocity. Subsequently, the mass properties of 27 collegiate level bats were input into the model for each subject trial. Using this information, the relative changes in kinetic inputs were quantified and the performance of the bats was estimated. Results showed that bat inertial properties varied considerably, and independent manipulation of individual properties was evident. In addition, subject kinetic inputs and bat performance measures were most affected by changes in mass center (CG) location, mass, and CG inertia. A modified definition of IGRIP based upon the ICR was presented, and practical implications for designers and practitioners were offered based upon these findings.

The acute effects of whole body vibration stimulus warm-up on skill-related physical capabilities in volleyball players

Whole body vibration (WBV) has been suggested to improve athletes’ neuromuscular strength and power. This study investigated the effect of single WBV stimulation on volleyball-specific performance. The participants were 20 elite male volleyball players who performed a 1-min warm-up exercise on a vibration platform at a frequency of 30 Hz and peak-to-peak displacement of 2 mm. After the warm-up exercise, the participants performed a blocking agility test (BAT), 10-m sprinting test, agility T-test, and counter movement jump test. We compared the participants’ performance at four time points (Pretest, Post 0, Post 1, and Post 2). The results revealed that the participants’ BAT performance and maximum rate of force development improved significantly 1 min after the vibration stimulation (p < 0.01). The WBV (frequency of 30-Hz, peak-to-peak displacement of 2 mm) intervention significantly improved the volleyball-specific defensive performance and speed strength of the participants. Accordingly, by undergoing WBV as a form of warm-up exercise, the technique and physical fitness of volleyball players can be improved.

Examining Changes in Bat Swing Kinematics in Different Areas of the Strike Zone in Collegiate Baseball Players

Background: According to the National Collegiate Athletic Association (NCAA) there are over 34,000 athletes who compete in baseball at the collegiate level. These individuals spend countless hours training to improve their ability at bat performance by use of a batting tee and their position preference. However, during a game situation an athlete may swing a bat through their strike zone depending on the pitch thrown by an opposing pitcher. Objective: The aim of this investigation was to examine changes in swing kinematics throughout an individual’s strike zone in collegiate baseball players. Variables of interest included resultant velocity at ball contact (RVBC) and the angle of the bat at ball contact (BABC). Methodology: A series of markers were placed on the tee and bat to record swing kinematic variables of interest. Participants completed a brief two-minute on-deck warm-up protocol before being counterbalanced into completing 15 swing trials in various regions of their respective strike zone. A ten-minute washout period was completed followed by another 15 swing trials throughout their strike zone until there was a total of 45 swing trials, having 5 swing trials completed in each of the nine regions of the strike zone. Results: Repeated measures analysis of variance were used to examine swing kinematic variables of interest. Significant differences were found in RVBC along with significant differences in BABC (p<.05). Conclusions: Knowledge of this information can allow both athlete and sport coach to identify areas of weakness when addressing their hitting performance in preparation for an at bat situation during a game.

Batting Cage Performance of Wood and Nonwood Youth Baseball Bats

The purpose of this study was to examine the batting cage performance of wood and nonwood baseball bats used at the youth level. Three wood and ten nonwood bats were swung by 22 male players (13 to 18 years old) in a batting cage equipped with a 3-dimensional motion capture (300 Hz) system. Batted ball speeds were compared using a one-way ANOVA and bat swing speeds were analyzed as a function of bat moment of inertia by linear regression. Batted ball speeds were significantly faster for three nonwood bat models (P< .001), significantly slower for one nonwood model, and not different for six nonwood bats when compared with wood bats. Bat impact speed significantly (P< .05) decreased with increasing bat moment of inertia for the 13-, 14-, and 15-year-old groups, but not for the other age groups. Ball-bat coefficients of restitution (BBCOR) for all nonwood were greater than for wood, but this factor alone did not correlate with bat performance. Our findings indicate that increases in BBCOR and swing speed were not associated with faster batted ball speeds for the bats studied whose moment of inertia was substantially less than that of a wood bat of similar length.