Kinematic Factors Associated with Hitting Hurdles During the Initial Phase of a 110-m Hurdle Race.

This study aimed to clarify the kinematic factors for the cause and effect of hitting hurdles during the initial phase of a 110-m hurdle run. Nine experienced male hurdlers participated in this study (body height: 1.74 ± 0.04 m, body mass: 67.4 ± 5.9 kg, age: 20.2 ± 1.4 years, personal best: 15.21 ± 0.47 s, seasonal best: 15.33 ± 0.55 s). Hurdlers undertook 12 trials of the initial phase of hurdling from the start to the second hurdle landing. Dual-sided sagittal plane motion was obtained from images from two high-speed cameras operating at 120 Hz. One 'hit' trial which had the largest horizontal displacement of markers fixed on the hurdle and one 'non-hit' trial which had the fastest time of hurdle clearance were extracted for each participant. Kinematic variables were compared between the two trials. Significantly lower height of the whole-body centre of mass at the take-off was found as a possible cause of hitting hurdles, caused by insufficient swing-up of the lead leg thigh. In contrast to conventional understanding, take-off velocity, take-off distance and the take-off angle were comparable between the 'hit' trial and 'non-hit' trial. Regarding the effect of hitting hurdles, it was observed that running velocity during hurdling was not substantially reduced. However, several characteristic movements were identified that might induce inefficient motion to re-accelerate running velocity during the following landing steps.

Dynamics of the support leg in soccer instep kicking.

We aimed to illustrate support leg dynamics during instep kicking to evaluate the role of the support leg action in performance. Twelve male soccer players performed maximal instep kicks. Their motions and ground reaction forces were recorded by a motion capture system and a force platform. Moments and angular velocities of the support leg and pelvis were computed using inverse dynamics. In most joints of the support leg, the moments were not associated with or counteracting the joint motions except for the knee joint. It can be interpreted that the initial knee flexion motion counteracting the extension joint moment has a role to attenuate the shock of landing and the following knee extension motion associated with the extension joint moment indirectly contributes to accelerate the swing of kicking leg. Also, appreciable horizontal rotation of the pelvis coincided with increase of the interaction moment due to the hip joint reaction force on the support leg side. It can be assumed that the interaction moment was the main factor causing the pelvis counter-clockwise rotation within the horizontal plane from the overhead view that precedes a proximal-to-distal sequence of segmental action of the swing leg.

Ball impact dynamics of instep soccer kicking.

PURPOSE: The purpose of this study was to reveal the foot-ball interaction during ball impact phase of soccer instep kicking. METHODS: Eleven soccer players performed maximal instep kicks. The behavior of kicking foot and ball during ball impact was captured using two ultrahigh-speed cameras at 5000 Hz. Foot motion was described three dimensionally, and the motion of the center of gravity of the ball (CGB) was estimated by the spherical shell model in which the ball deformation was taken into account. The peak ball reaction force acting on the foot was estimated from Newton's equation of motion in which the peak CGB acceleration in sagittal plane was calculated from its velocity slope near the peak ball deformation. RESULTS: During ball impact (9.0 +/- 0.4 ms), the foot was passively abducted and everted. Moreover, an unknown feature--slight dorsal flexion before distinctive plantarflexion--was quantified in most trials. The CGB velocity exceeded that of the foot when the ball was maximally deformed (6.2 +/- 0.6 cm). The magnitude of peak ball reaction force reached 2926 +/- 509 N, which corresponds to approximately twice as that of the mean force (1403 +/- 129 N). From the changes of the foot velocity, the CGB velocity, and the ball deformation, the ball impact phase can be divided into four phases. CONCLUSIONS: The ultrahigh-speed video and methodology in this study documented complex three-dimensional foot motions to impact in soccer instep kicks, dynamic foot-ball interaction, and larger peak ball reaction force on the foot that previously estimated. It can be considered that effectual duration to accelerate the ball is roughly three fourths of visually determined ball contact time.

The effect of fatigue on the underwater arm stroke motion in the 100-m front crawl.

The purpose of this study was to indicate the effect of fatigue on the underwater right arm stroke motion during the 100-m front crawl. The arm stroke motions of eight male competitive swimmers were captured three-dimensionally at 60 Hz in the positions of 15 m and 65 m from the start. The hand velocity, the arm angular velocities and the relative contribution of the arm angular velocities to the hand velocity were computed at each instant during the arm stroke motion. A significant decrease of the hand velocity and the peak angular velocity of shoulder adduction were observed in the second half than in the first half. The contribution of shoulder adduction was especially large in the pull phase and subsequently that of shoulder horizontal abduction became dominant in the push phase. However, in the second half, the contribution of shoulder adduction tended to decrease while that of shoulder internal rotation tended to increase. Thus, it is quite likely that the arm stroke motion of swimmers were driven to be influenced by induced fatigue and resulted in an increase in the contribution of shoulder internal rotation to compensate the decreased contribution of shoulder adduction angular velocity.