Kinetic analysis of individual upper limbs during baseball tee-batting motion at different hitting-point heights

Abstract

Kinetic analysis of individual upper limbs during baseball tee-batting motion at diŠerent hitting-point heights. Japan J. Phys. Educ. Hlth. Sport Sci. 59: 431 452, December, 2014 AbstractThe purpose of this study was to clarify the kinetic features of the upper limbs at diŠerent hitting-point heights (high, middle, and low) during baseball tee-batting. Twenty-three collegiate male baseball players (age: 19.8±1.3 yr, height: 1.74±0.04 m, weight: 74.1±6.2 kg, athletic career: 12.0± 2.1 yr) participated. Three-dimensional coordinate data were captured using a VICON MX system (12-camera, 250 Hz), and kinetic data for each hand were collected using an instrumented bat equipped with 28 strain gauges (1000 Hz). Three tee-batting heights were set for each subject based on the upper and lower limits of the strike zone according to the rules of baseball. Kinetic variables for the upper limbs, such as joint torque, joint torque power, and mechanical work, were calculated. The period of forward swing motion was divided into down-swing and level-swing phases. The results are summarized as follows: 1) The extension torque and positive torque power at each individual shoulder joint were sig-niˆcantly greater at the low hitting-point height than at other heights. 2) The positive torque power for extension torque at each individual elbow joint in the last half of the down-swing phase was signiˆcantly greater at the low hitting-point height than at other heights. 3) Negative power for adduction/abduction torque at each individual shoulder joint in the level-swing phase was observed at the low hitting-point height. 4) The mechanical work done by joint torque about the ‰exion/extension and adduction/abduc-tion axes at the shoulder, the ‰exion/extension axis at the elbow, and the palmar/dorsal ‰exion and radi-al/ulnar ‰exion axes at the wrist showed large and positive values, and diŠered signiˆcantly among hitting point heights. These results indicate that 1) the ‰exion/extension torque at each individual shoulder joint contributes greatly to adjustment of the translational movement of the bat in the vertical direction during the down-swing phase, 2) the adduction/abduction torque at each individual shoulder joint exerts a larger proportion of the longitudinal force of the bat to withstand centrifugal force at a low hitting-point height than at other heights in the level swing phase, and 3) consequently, it tends to be more di‹cult to adjust the bat to the hitting-point at a low height in comparison with other heights. Key wordsclosed loop problem at upper limbs, inverse dynamics calculation, instrumented bat, stationary ball batting キーワード上肢閉ループ問題，逆動力学演算，センサー・バット，静止球打撃