Biomechanics of the baseball swing

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The purpose of this research was to describe the kinematics of the baseball swing. In particular, this study aimed to determine differences in bat swing kinematics in hitters of varying ability. Further, changes in swing pattern that occur when using bats of varying mass where also observed. Twenty sub-elite male baseballers participated in the study (22.3 ± 5.3 yr, 1.82 ± 0.07 m, 83.5 ± 10.9 kg). Three baseball bats of equal length (0.838m) and varying mass (Bat1 = 0.795kg, Bat2 = 0.847kg, Bat3 = 0.943kg) were used. Each subject performed 10 maximal swings with each bat at a ball on a hitting tee replicating a line drive. Infrared cameras obtained high speed three-dimensional data to quantify the biomechanics during the baseball swing, One-way ANOVA was used to determine kinematic differences between conditions. In addition, the participants were ranked prior to testing based on a novel coach's rating scale and seasonal batting average. They were subsequently separated into a relatively good group of hitters (n=10) and a relatively poor group of hitters (n=10) for comparison. Importantly, the two groups were significantly different in terms of coach's rating (p<0.01) and batting average (p<0.05). The results showed a significant difference in maximum bat swing velocity (p<0.05) with good hitters having a higher velocity (36.8 m•s-1) in comparison to relatively poor hitters (33.8 m•s-1). Left elbow maximum angular velocity was significantly higher (35.9%) amongst relatively good hitters (p<0.05). Good hitters also had a right knee angle of 106° at ball contact which was significantly (p<0.05) higher than relatively poor hitters (100°). There were no between-group differences for wrist and hip joint velocities at ball contact. The results also showed a difference in maximum bat swing velocity (p<0.01) between Bat1 (36.0m•s-1)and Bat3 (34.4m•s-1) Resultant ball velocity was 17% higher using Bat1 compared to Bat3 (p<0.05). Subject head movement was lower using Bat1 (8 cm) when compared to Bat3 (10 cm). Maximum linear left hip velocity was significantly higher (p<0.01 ) when using Bat3 compared to other bats. In contrast, maximum linear right hip velocity was lower (p<0.0 1) when using Bat3. This study established that bat swing velocity is a key characteristic of the baseball swing when identifying skill level and performance between hitters. Additionally, good hitters display greater lead elbow maximum angular velocity. Future research should develop and evaluate specific baseball training programs designed primarily to improve these two aspects of the baseball swing. Further, this study has identified aspects of the baseball swing that differ when using bats of varying mass. Notably, a relationship exists between bat mass and hip linear velocity which could be a potential mechanism for underlying training effects. Further studies are needed to determine acute and longitudinal kinematic effects of using bats of varying mass.
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