The purpose of this study was to quantify the systematic and random errors by manual measurement with a use of stopwatch in 50 m sprint test. Eight sprinters implemented 16 trials of 50 m sprint tests over days, respectively (a total of 128 times of tests were conducted). Eight examiners measured sprint times with their stopwatches every set, and in total 1014 of results could be successfully obtained. Concurrently, the video-based sprint time measurements were carried out in order to obtain the true values of the 128 trials of sprints. The systematic error was defined as the mean difference between the true values (videobased measurements) and the manual values (stopwatch measurements), and the random error as the averaged standard deviations of each error within respective subjects. As results, the systematic error was estimated at -0.27 s and the random error was estimated at 0.07 s. The findings of this study suggest that sprint tests with a stopwatch be assessed, taking the systematic and random errors quantified in this study into consideration.
Optimal control of muscular strength at submaximal levels is a more important ability in actual practice of several physical activities and sports performance than maximal strength. Based on actual situations, in this study, we examined the influence of individual history of exercise during various school ages on the coordination ability in grip strength of college students. We measured the maximal voluntarily handgrip strength of 438 healthy university students, and their voluntary isometric grip strength performed at the target values (30%, 50%, and 70% of maximal grip strength) depending on subjective effort. The effects of several variables, as exemplified by the target values, sex, maximal handgrip strength, and estimated exercise volume (the product of exercise period and intensity) in each school age (preschool, lower and upper elementary school grades, junior high school, high school, and university), on the differences between the target and measured values at several grip strength levels were statistically considered in a multilevel model analysis. These results suggest that the exercise volume in the lower elementary school grades had a large effect on muscular contraction control later in adolescence. In addition, these findings indicate the need to reexamine the practice of exercise among elementary school students.
Objective: The present study aimed to clarify the influence of different lengths of the muscle tendon complex (LMTC) by investigating the relationship of the amplitude of the surface electromyogram (EMG) of the biceps femoris long head (BF), semitendinosus (ST), and semimembranosus muscles (SM). Methods: Thirteen healthy young men (age, 21.1 ± 1.0 years; height, 173.1 ± 4.4 cm; weight, 71.1 ± 8.7 kg) performed the maximum isometric knee flexion (MVC) using a dynamometer (CON-TREX). Knee flexion torque data were collected from ten combinations of knee flexion angles (K) at 5, 30, 60, 90, and 105 degrees at both the sitting (S) and the prone position (P). The EMGs were acquired by attaching electrodes to the middle, proximal, and distal parts of each muscle. The LMTCs were estimated using the regression equation of Hawkins and Hull (1990). Results: The LMTC was the shortest at P-K105 and the longest at S-K5. High MVC torque was indicated with extended LMTC. However, different EMG amplitude patterns were present in the BF, ST, and SM during MVC torque production in different LMTCs. Conclusion: The influence of different lengths of the LMTC on the EMG of BF, ST, and SM was attributed to different morphological and structural features among the muscles and can be interpreted as being indicative of the angle–force relationship due to the length–tension curve of each muscle.
In this study, we revealed relationship between the center of pressure (COP) sway and stability in standing posture on an unstable surface, and the influence of standing posture on a stable surface that affects the COP sway and stability in standing posture on an unstable surface.
The subjects were 20 middle-aged women. We took pictures of standing posture in the sagittal plane and categorized into good type (Group G : n = 7) and bad type (Group B : n = 13). In addition, we measured COP sway and posture alignment to assessment the standing posture. An unstable tilt board is used for measuring two types of dynamic postural control ability. First, we tested COP sway on an unstable surface. We examined standing posture and followed the COP to the target. Then we tested for stability in standing posture on an unstable surface. We examined standing posture on the unstable surface and kept the COP in extent of supporting base. As a result, COP sway on the unstable surface was associated with the COP position on the unstable surface (r = 0.77, p < 0.05). Standing posture was located in front of the ear canal and knee joint of Group B compared to Group G (p < 0.05). In addition, Group G was better than Group B in the first test (p < 0.05), but no significant difference at all was found in the second test (p > 0.05). Therefore, COP sway on an unstable surface affects standing on a stable surface, but stability in standing posture on an unstable surface is less likely.
To evaluate the excitement caused by baseball plays, we examined the relationships among the audience's cheering volume, changes in win probability, and events such as achieving a hit during a professional baseball game. The total number of events and mean cheering volume throughout the game were 70 and 86.99 (± 6.35) dB, respectively. There was a significant correlation between the cheering volume and win probability. On comparing the former among events, the volume was significantly higher when achieving hits compared with outs or walk/hits by pitch. It was also significantly higher when there were runners in a scoring position than when there were no such runners. Based on the results, the audience may become more excited when win probability markedly changes, there is a hit, or there are runners in a scoring position.