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Mana Ogawa, Chiaki Ohtaka, Motoko Fujiwara, and Hiroki Nakata

The authors investigated the kinematic characteristics of the standing long jump in preschool children. Sixty 4-year-old children (boys: 30 and girls: 30) and sixty 5-year-old children (boys: 30 and girls: 30) participated in the present study. The authors focused on three differences in kinematics: between 4- and 5-year-old children, between boys and girls, and between high and low jumping performance groups at the same age. The kinematic data included the maximum flexions of the knee and hip before takeoff, at takeoff, and on landing; angular displacement of the upper body; takeoff speeds in horizontal and vertical directions; and takeoff angle of the greater trochanter. Anthropometric variables and kinematic data were separately analyzed with factors of age, sex, and group. The authors also performed multiple regression analysis to identify predictors of the jump distance. The movement speed of the greater trochanter in a horizontal direction, the maximum flexion angle of the hip before takeoff, and the hip angle on landing were identified as significant predictors of the jump distance among young children. These findings suggest that knowing how to use the hip and awareness of the horizontal direction are key factors to improve the long jump distance in young children.

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Takatoshi Higuchi, Jun Morohoshi, Tomoyuki Nagami, Hiroki Nakata, and Kazuyuki Kanosue

The effectiveness of fastballs of equivalent speed can differ; for example, one element of this difference could be due to the effect of rate and orientation of ball spin on launched ball trajectory. In the present experiment, baseball batters’ accuracy in hitting fastballs with different backspin rates at a constant ball velocity of 36 m/s was examined. Thirteen skilled baseball players (professionals, semiprofessionals, and college varsity players) participated in the study. The movements of bat and ball were recorded using two synchronized high-speed video cameras. The Pearson product-moment correlation coefficient (r) was calculated and used to analyze the relationship between ball backspin rate and the vertical distance between ball center and sweet spot at the moment of ball-bat impact. Ball backspin rate was positively correlated with increases in the distance from the optimal contact point of the swung bat (sweet spot) to the actual point of contact (r = .38, P < .001). Batters were most effective at the usual backspin rate for the ball velocity used. The decrease in accuracy of the batter’s swing that was observed when the fastball’s backspin deviated from the usual rate likely occurred because experienced batters predict ball trajectory from perceived ball speed.

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Takuma Hoshiba, Hiroki Nakata, Yasuaki Saho, Kazuyuki Kanosue, and Toru Fukubayashi

Context: Deficits in knee position sense following reconstruction of the anterior cruciate ligament (ACL) can delay an athlete’s return to sport participation and increase the risk of reinjury. Deficits in position sense postreconstruction have been evaluated using either a position-reproducing or position-matching task. Objective: The aim of our study was to combine both to determine which assessment would be more effective to identify deficits in knee position sense. Design: Longitudinal laboratory-based study. Participants: Eleven athletes (6 men and 5 women; mean age, 20.5 [1.2] y), who had undergone ACL reconstruction with an ipsilateral hamstring autograft, and 12 age-matched controls. Interventions: Position sense was evaluated at 6 and 12 months postreconstruction and once for the control group. In addition, peak isokinetic knee extension and flexion strength, at 60°/s and 180°/s, was assessed for the ACL reconstruction group to evaluate possible influences of muscle strength on knee joint position sense. Main Outcome Measures: The variables include the angular differences between the reference limb and indicator limb, and peak torque values of isokinetic knee extension and flexion. Results: Significant matching differences were identified at 6 months postsurgery on the position-matching task, but not at 12 months postsurgery. No significant between-group and within-subject differences were identified on the position-reproducing task. No significant matching errors were identified for the control group. There was no correlation between errors in position sense and maximum isokinetic strength. Conclusion: The position-matching task is more sensitive than the position-reproducing task to identify deficits in knee position sense over the first year following ACL reconstruction surgery.

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Tomoyuki Nagami, Takatoshi Higuchi, Hiroki Nakata, Toshimasa Yanai, and Kazuyuki Kanosue

Although the lift force (FL) on a spinning baseball has been analyzed in previous studies, no study has analyzed such forces over a wide variety of spins. The purpose of this study was to describe the relationship between FL and spin for different types of pitches thrown by collegiate pitchers. Four high-speed video cameras were used to record flight trajectory and spin for 7 types of pitches. A total of 75 pitches were analyzed. The linear kinematics of the ball was determined at 0.008-s intervals during the flight, and the resultant fluid force acting on the ball was calculated with an inverse dynamics approach. The initial angular velocity of the ball was determined using a custom-made apparatus. Equations were derived to estimate the FL using the effective spin parameter (ESp), which is a spin parameter calculated using a component of angular velocity of the ball with the exception of the gyro-component. The results indicate that FL could be accurately explained from ESp and also that seam orientation (4-seam or 2-seam) did not produce a uniform effect on estimating FL from ESp.