The purpose of this study was to test whether a light finger touch on one’s own body (upper legs) reduces postural sway. Ten healthy males participated. In the first part of the study, the participants stood upright with their eyes closed on a force platform while ground reaction force data were collected. Two conditions differing in the placement of the arms and fingers were tested. In the no-touch condition, the participants kept their hands in loose fists. In the finger-touch condition, the participants lightly touched the lateral sides of the upper legs with all fingers. Postural sway measures were calculated from the ground reaction force data. In the second part of the study, the participants stood upright on a pneumatic balance disk while ground reaction force data were collected. Experimental and measurement protocols were identical to those used in the first part of the study. The results showed that light finger touch on the upper legs significantly reduced postural sway on the balance disk up to ~7%. The data from this study suggest that decreased postural sway due to finger contact may improve balance control during other standing tasks.
Akinori Nagano, Shinsuke Yoshioka, Dean Charles Hay and Senshi Fukashiro
Shohei Shibata, Yuki Inaba, Shinsuke Yoshioka and Senshi Fukashiro
This study had two objectives: (a) revealing the difference in finger segments between the conventional and finger models during aimed throwing and (b) examining the central nervous system’s timing control between the wrist torque and finger torque. Participants were seven baseball players. Finger kinetics was calculated by an inverse dynamics method. In the conventional model, wrist flexion torque was smaller than that in the finger model because of the error in ball position approximation. The maximal correlation coefficient between the wrist torque and finger torque was high (r = .85 ± .10), and the time lag at maximal correlation coefficient was small (t = 0.36 ± 3.02 ms). The small timing delay between the wrist torque and finger torque greatly influenced ball trajectory. We conclude that, to stabilize release timing, the central nervous system synchronized the wrist torque and finger torque by feed-forward adjustments.
Yuki Inaba, Shinsuke Yoshioka, Yoshiaki Iida, Dean C. Hay and Senshi Fukashiro
Lateral quickness is a crucial component of many sports. However, biomechanical factors that contribute to quickness in lateral movements have not been understood well. Thus, the purpose of this study was to quantify 3-dimensional kinetics of hip, knee, and ankle joints in side steps to understand the function of lower extremity muscle groups. Side steps at nine different distances were performed by nine male subjects. Kinematic and ground reaction force data were recorded, and net joint torque and work were calculated by a standard inverse-dynamics method. Extension torques and work done at hip, knee, and ankle joints contributed substantially to the changes in side step distances. On the other hand, hip abduction work was not as sensitive to the changes in the side step distances. The main roles of hip abduction torque and work were to accelerate the center of mass laterally in the earlier phase of the movement and to keep the trunk upright, but not to generate large power for propulsion.
Mitsuo Otsuka, Jae Kun Shim, Toshiyuki Kurihara, Shinsuke Yoshioka, Makoto Nokata and Tadao Isaka
In sprinters with different levels of block acceleration, we investigated differences in their three-dimensional force application in terms of the magnitude, direction, and impulse of the ground reaction force (GRF) during the starting block phase and subsequent two steps. Twenty-nine participants were divided into three groups (well-trained, trained, and nontrained sprinters) based on their mean anteroposterior block acceleration and experience with a block start. The participants sprinted 10 m from a block start with maximum effort. Although the mean net resultant GRF magnitude did not differ between the well-trained and trained sprinters, the net sagittal GRF vector of the well-trained sprinters was leaned significantly further forward than that of the trained and nontrained sprinters during the starting block phase. In contrast, during the starting block phase and the subsequent steps, the transverse GRF vectors which cause the anteroposterior and mediolateral acceleration of the whole-body was directed toward the anterior direction more in the well-trained sprinters as compared with the other sprinters. Therefore, a more forward-leaning GRF vector and a greater anteroposterior GRF may particularly allow well-trained sprinters to generate a greater mean anteroposterior block acceleration than trained and nontrained sprinters.