The purpose of the present case study was to clarify calligraphic skill of a Japanese calligrapher quantitatively. For this purpose, the brushwork of an expert calligrapher was kinematically compared with that of a novice as well as an intermediate. Three subjects (an expert calligrapher, an intermediate, and a novice) participated in the experiment. A motion capture system was used to capture the motion of a brush during writing a kanji on a Japanese writing paper. As results, absolute writing speed tended to fasten and the variability of the vertical displacement of a brush decreased along with the calligraphic skill. The frequency analysis of the horizontal velocity of a brush revealed that a dominant region shifted toward a low-frequency direction in the expert in comparison with the intermediate although their absolute writing speeds were not significantly different. These results suggest that the expert calligrapher could move the brush with rather slow than rapid change of velocity on the horizontal plane accompanying with lowering the vertical brush displacement.

In baseball, the flight distance of batted balls is influenced by not only the batted ball velocity but also the spin. Previous studies reported that balls batted toward the opposite field (right field for the right-handed batter) had greater side spin and curved horizontally. If batters could impart less side spin to the ball, flight distance would be expected to increase because the ball would travel more linearly. The purpose of this study was to investigate how the spin of a batted ball is affected by the vertical bat angle at impact. A pitching machine was used to launch balls toward a fixed bat. The bat was positioned at six different angles under two conditions; the bat's long axis was adjusted horizontally and the bat head was declined 40° lower than the bat grip. The batted ball spins resulting from the batted ball angles were compared between the conditions. There were significant correlations between the horizontal batted ball angle and the side spin of the batted balls in both conditions. There was no significant difference between the slopes of the regression lines for the conditions. In brief, balls batted toward the same direction had similar spin regardless of the conditions. Therefore, it is suggested that the batters should not attempt to control batted ball spin, and increasing their bat swing speed would be still the most important key factor to hit balls long distances toward the various directions.

This study aimed to elucidate the role of joints and arm swing motion in controlling linear and angular momentum in vertical jumps. Twenty-eight participants performed maximal effort vertical jumps, and data on jumping motion (500 Hz) and ground reaction force (1000 Hz) were collected. The contributions of each joint torque to the linear and angular momentum of the whole body, arm, trunk, and leg were calculated by induced acceleration analysis. The role of the ankle joint torque was to acquire the vertical momentum of the whole body by external forces. The role of the knee joint torque was to regulate the horizontal and angular momentum of the whole body. The role of the hip joint torque was to distribute the momentum of the leg to the trunk by internal forces. The role of the virtual trunk joint torque was to distribute the angular momentum of the lower limb to the trunk by internal forces, and to control the distribution of horizontal momentum between segments. The arm joint torques did not affect the acquisition and distribution of these linear and angular momenta. However, the arm swing motion may have played a role as a counterweight to cancel the horizontal and angular momentum due to the motion-dependent forces acting on the whole body.

The purpose of this study was to investigate the relationship between fascicle length (Lf) –to–moment arm (MA) ratio (Lf/MA) of soleus muscle and isokinetic plantarflexion torque in vivo. Twenty–two healthy men performed isokinetic (concentric) plantarflexions at 30°/s (Slow) and 150°/s (Fast) in a 90° flexed knee position. The Lf of the soleus and its shortening velocity were determined with ultrasonography at rest and during the plantarflexions, respectively. The MA of the Achilles tendon was measured with magnetic resonance imaging at rest. The results showed that Lf/MA was significantly correlated with the fascicle shortening velocity normalized by Lf at rest (Slow: r = ‒0.600; Fast: r=‒0.583). The normalized fascicle shortening velocity was significantly correlated with the muscle force normalized by physiological cross–sectional area (PCSA) of the soleus (Slow: r = ‒0.553; Fast: r = ‒0.788). The normalized muscle force was significantly correlated with the plantarflexion torque normalized by PCSA (Slow: r = 0.947; Fast: r = 0.957). Furthermore, there were significant correlations between Lf/MA and the normalized plantarflexion torque (Slow: r = 0.631; Fast: r = 0.600). These results suggest that large Lf/MA of soleus muscle is beneficial for attaining low fascicle shortening velocity and thus exerting large muscle force and joint torque during the isokinetic plantarflexion.

This study aimed to characterize basic postural recovery responses in younger adults before the first forward step landing (FL) after tripping in gait, or the pre-landing phase. Twelve young participants were tripped while walking and were required to return to normal walking after tripping. We recorded the kinematics and kinetics of their recovery responses using a 17-camera motion capture system and a force platform. We compared the whole-body angular momentum (WBAM) around the whole-body center of mass (WBCM) and the whole-body linear momentum (WBLM) in the tripping trials, with those in the normal walking trials. We also examined the angular momentum (AM) and linear momentum (LM) of the body segment groups and the joint torques. The forward WBAM around the WBCM increased by tripping started decreasing early in the pre-landing phase. When the forward WBAM decreased in the tripping trials, the backward AM of the tripped leg increased, while the increase in the forward AM of the head-neck plus trunk (HT) and support leg was suppressed. There was no significant difference in the forward WBAM around the WBCM at FL between the tripping trials and the normal walking trials. On the other hand, the forward and downward WBLM at FL were 1.1 and 2.5 times larger in the tripping trials than in the normal walking trials, respectively. In addition, all of the forward AM and the forward and downward LM of the HT at FL were significantly larger in the tripping trials. These results indicated that younger adults could decrease the forward WBAM increased by tripping to a level comparable to that at FL of normal walking. It is suggested that suppressing the increase in the forward angular velocity of the HT and support leg during a rapid forward swing of the tripped leg contributes to decreasing the forward WBAM around the WBCM. It is also suggested that although the WBAM changed due to tripping can be controlled during the pre-landing phase, suppressing the forward and downward WBLM as well as controlling the AM and LM of the HT after FL would be required for recovering to normal walking.

The purpose of this study was to clarify the relationship between the change in direction of the velocity of center of mass (CoM) and the force acting on the center of mass during the take-off phase in a running single-leg jump (RSLJ) with different run-up speed and jumping task. Nine male collegiate jumpers performed RSLJ in two tasks, to jump forward and upward, respectively, with four different run-up speeds. Three-dimensional coordinates of the end positions of the body segments and the ground reaction force (GRF) were obtained using the motion capture system and force platform. The GRF and gravity acting on the CoM were divided into the normal and tangential force relative to the velocity of CoM. The amount of change in direction of CoM velocity was significantly correlated with the normal impulse during take-off phase. As run-up speed or take-off angle increase, the normal impulse and the negative tangential impulse increased in the first phase of take-off. The normal impulse in the second phase was decreased by the shortening of support time in the faster run-up speed. These results suggested that it is important for the change in CoM velocity direction to increase the normal force in the first phase of the take-off and it might be useful for the evaluation of the RSLJ by means of dividing the force into normal and tangential components relative to the velocity.