The purpose of the study was to describe age-related changes in knee strength and thigh muscle volume on elite soccer players from late adolescence to adulthood. Totally 191 soccer player participated in the study and were divided into 5 age groups, i.e. under 16 (U15), 17 (U16), 19 (U18), and 22 (U21) yrs and over 22 (O22) yrs. All of U21 and O22 subjects were professional soccer players. Maximal knee extension (KE) and flexion (KF) concentric torque were measured using isokinetic dynamometer at velocities of 1.05, 3.14, and 7.85 rad/s in both of the dominant and non-dominant legs. Femur length and cross-sectional areas of the quadriceps femoris and hamstrings at the upper, middle, and lower range of the thigh were determined by magnetic resonance imaging, from which the volume of quadriceps femoris (esQF) and hamstrings (esHAM) were estimated. From U15 to U18 neither KE nor KF at 1.05 rad/s increased significantly, although those at the other faster velocities increased significantly regardless of whether the data were expressed as absolute or adjusted value to body weight. In addition, esQF and esHAM also did not increase significantly from U15 to U18. However, the largest increases were observed between U18 and U21 in KE and KF at all the velocities as well as esQF and esHAM. Furthermore, when KE and KF were divided to esQF and esHAM respectively, the values also increased significantly from U15 to U21, suggesting higher knee strength in the professional soccer players were attributed to the concomitant development of thigh muscle volume with the increased neural activation. The ratio of KF to KE and the ratio of esHam to esQF increased slightly from U15 to O22, indicating the predominant development of knee flexor muscles on soccer players after late adolescence. The data presented in this study implied that increasing knee strength with emphasis on both thigh muscle hypertrophy and adaptation of neuromuscular function was essential for younger players to achieve higher soccer playing standards.
The purpose of this study was to examine the influence of time pressure on the psychological, physiological, and behavioral aspects of a dart-throwing task. Participants (N=25) performed 140 acquisition trials (10 trials×14 blocks) followed by 10 test trials under time pressure. Time pressure was induced by instructing the participants to complete 10 test trials within the duration of the longest acquisition block. Dart-throwing movements were videotaped for 2-dimensional kinematic analysis. The results showed that the dart scores decreased from the last acquisition block to the test (p<.01), and that heart rate (p<.01) increased from the acquisition to the test. An analysis of a questionnaire revealed that conscious control of movements (p<.05) and attention to time (p<.01) increased from the acquisition to the test. The inter-trial dart throwing interval (p<.01) decreased from the acquisition to the test. In addition, the minimum angle (p<.01) and mean angular velocity (p<.05) of the elbow joint in the take-back phase increased from the acquisition to the test, indicating that the take-back movement became smaller and faster under time pressure. Although the participants did not have to decrease the inter-trial interval and movement time to complete the test trials within the time limit, it appeared that these behavioral changes were caused by time pressure. In addition, contrary to the inhibition of movement velocity due to performance pressure (Tanaka and Sekiya, 2006), time pressure facilitated movement velocity in the present study, suggesting that different kinds of stressors lead to different movement characteristics.
A study was conducted to examine coping with interpersonal stress among students in physical education (PE) classes. Students (n=447) responded to 58 items that had been developed on the basis of free descriptions given by junior high school students about how they cope with interpersonal stress. Factor analysis revealed 6 coping factors that consisted of 28 coping items. These factors were named “introspection”, “neglect”, “avoidance of company”, “assertion”, “approach” and “shrug-off”. In addition, ANOVA clarified that female students (n=242) selected “avoidance of company” and “shrug-off”, more frequently than male students (n=205). Upper grade students (2nd grade students, n=146 ; 3rd grade students, n=226) showed a tendency not to use “assertion” as much as 1st grade students (n=75), and 3rd grade students tended to adopt shruging off for coping with interpersonal stress more regularly than 2nd grade students. These results suggest that although students in PE classes cope in various ways with interpersonal stress, differences in gender and/or grade have a hand in strategy selection.