The present study investigated characteristics of the relative age effect (RAE) among a general sample of Japanese elementary and junior high school students. Japan applies a unique annual age-grouping by birthdates between April 1 and March 31 of the following year for sport and education. Anthropometric and physical fitness data were obtained from 3,610 Japanese students, including height, weight, the 50-m sprint, standing long jump, grip strength, bent-leg sit-ups, sit and reach, side steps, 20-m shuttle run, and ball throw. We examined RAE-related differences in these data using a one-way analysis of variance by comparing students with birthdates in the first (April-September) versus second (October-March of the following year) semesters. We observed a significant RAE for boys aged 7 to 15 years on both anthropometric and fitness data, but a significant RAE for girls was only evident for physical fitness tests among elementary school and not junior high school students. Thus, a significant RAE in anthropometry and physical fitness was evident in a general sample of school children, and there were RAE gender differences among adolescents.

We investigated the characteristics for force generation and relaxation using graded isometric contractions of the knee extensors. Participants performed the following tasks as quickly and accurately as possible. For the force generation task, force was increased from 0% to 20%, 40% and 60% of the maximal voluntary force (MVF). For the force relaxation task, force was decreased from 60% to 40%, 20% and 0%. The following parameters of the recorded force were calculated: error, time, and rate of force development. The error was consistently greater for force relaxation than generation. Reaction and adjustment times were independent of the tasks. The control strategy was markedly different for force relaxation and generation, this tendency was particularly evident for the lower limb compared to the upper limb.

Characteristics and motor strategies for force generation and force relaxation were examined using graded tasks during isometric force control. Ten female college students (M age = 20.2 yr., SD = 1.1) were instructed to accurately control the force of isometric elbow flexion using their right arm to match a target force level as quickly as possible. They performed: (1) a generation task, wherein they increased their force from 0% maximum voluntary force to 20% maximum voluntary force (0%-20%), 40% maximum voluntary force (0%-40%), or 60% maximum voluntary force (0%-60%) and (2) and a relaxation task, in which they decreased their force from 60% maximum voluntary force to 40% maximum voluntary force (60%-40%), 20% maximum voluntary force (60%-20%), or to 0% maximum voluntary force (60%-0%). Produced force parameters of point of accuracy (force level, error), quickness (reaction time, adjustment time, rate of force development), and strategy (force wave, rate of force development) were analyzed. Errors of force relaxation were all greater, and reaction times shorter, than those of force generation. Adjustment time depended on the magnitude of force and peak rates of force development and force relaxation differed. Controlled relaxation of force is more difficult with low magnitude of force control.

We investigated the relationship between basketball free-throw accuracy and anthropometry, physical fitness tests, and performance variables among 16 collegiate female basketball players. Each participant performed 20 basketball free throws. Anthropometric measures were height and weight; physical fitness tests were sit-and-reach, back strength, and grip strengths; other basketball performance variables were the phases of the pre-shoot routine: (a) time taken, (b) minimum angle when taking the ball back, (c) angle at ball release, (d) angular displacement during the forward arm swing, and (e) angular velocity at ball release on the elbow, shoulder, hip, knee, and ankle. We analyzed the correlation between free-throw accuracy and data on anthropometry and physical fitness, the time period and variability of the pre-shot routine, and kinematic data. There were negative correlations between free-throw accuracy and mean preshot time, and variability of the pre-shot time, indicating that participants with a shorter and less variable pre-shot time showed a higher free-throw accuracy. Angular displacement of the shoulder during the forward swing and angular velocity of the knee at ball release showed positive correlations with free-throw accuracy. There was also a negative correlation between freethrow accuracy and variability of angular displacement during the forward swing at the elbow, indicating that participants with smaller variability of angular displacement of the elbow showed higher free-throw accuracy. Some performance variables, including routine duration, angular displacement of the shoulder and elbow, and angular velocity of the knee, were related to freethrow accuracy.

No abstract