Countermovements are often used for athletic performance improvement. Many tennis players utilize a “split-step (SPLIT),” a small preparatory hop, to prime themselves for quick lateral reactions. Though baseball players perform similar lateral reactions, use of a split-step has not yet been evaluated. PURPOSE: The purpose of this study was to determine if implementing a split-step affected reaction time, force production, and muscle activation in baseball players. METHODS: Male subjects (n=12, 20.47 ± 1.01 yrs, mean± SD) with at least 2 years of baseball experience participated. EMG recordings of the following muscles related to knee extension and plantar flexion were collected: anterior tibialis (AT), medial gastrocnemius (MGAS), lateral gastrocnemius (LGAS), vastus lateralis (VL), biceps femoris (BF), and gluteus maximus (GLUT). Stationary balls were positioned in six locations, each 1m from a force plate: left, right, and forward of the plate with 3 on the ground and 3 at 1m above the ground. Subjects performed three CONTROL and three SPLIT trials. An on-screen 3-2-1 visual countdown was provided, followed by an arrow to simulate the trajectory of a hit ball, pointing randomly in one of the six directions. During CONTROL, subjects reacted towards the correct ball immediately upon visualization of the arrow. During SPLIT, subjects performed a small hop on "1" and then reacted as quickly as possible in the direction of the arrow. Mean muscle activation, force production (ground reaction forces), and reaction time were recorded. Results were evaluated with a RM-ANOVA with post-hoc tests and Bonferroni correction. RESULTS: Results are reported as percent difference between conditions. Muscle activation was significantly greater during SPLIT in the up/forwards direction for GLUT (40.22 ± 30.29 %), in the up/dominant direction for BF (50.92 ± 24.51 %) and GLUT (39.05 ± 31.75 %), and in the up/non-dominant direction for AT (28.65 ± 22.60 %, p values significant at p<0.0083). Vertical force production was significantly greater in SPLIT in the up (19.36 ± 10.39%), down (20.40 ± 21.13%), and down/dominant directions (13.13 ± 13.15%, p values significant at p<0.05). Reaction time and ground shear forces were similar between conditions. CONCLUSION: Increases in muscle activation were seen primarily in variations of the up direction, therefore utilization of a split-step may be more beneficial when reacting towards a high hit ball. Reaction time is the most important aspect of a baseball player's movement towards a hit ball. The overall trend of shortened reaction time may indicate that a split-step should be implemented, however practice is key.

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