The Effect of Increasing Jump Steps on Stance Leg Joint Kinetics in Bounding.

Jump distance per step in bounding exercises from the standing position increases with increasing number of steps. We examined the hypothesis that the joint kinetic variables of the stance leg would also increase accordingly. Eleven male athletes (sprinters and jumpers) performed bounding exercise, starting from the double-leg standing posture, and covered the longest distance possible by performing a series of seven forward alternating single-leg jumps. Kinematic and kinetic data were calculated using the data by a motion capture system and force platforms. Hip extension joint work were decreased at third step (1st: 1.07±0.22, 3rd: 0.45±0.15, 5th: 0.47±0.14 J•kg-1; partial η2: 0.86), and hip abduction joint power were increased (1st: 7.53±3.29, 3rd: 13.50±4.44, 5th: 21.37±9.93 W•kg-1; partial η2: 0.58); the knee extension joint power were increased until the third step (1st: 14.43±4.94, 3rd: 17.13±3.59, 5th: 14.28±2.86 W•kg-1; partial η2: 0.29), and ankle plantar flexion joint power increased (1st: 34.14±5.33, 3rd: 37.46±4.45, 5th: 40.11±5.66 W•kg-1; partial η2: 0.53). These results contrast with our hypothesis, and indicate that increasing the jump distance during bounding exercises is not necessarily accompanied by increases in joint kinetics of stance leg. Moreover, changes in joint kinetics vary at different joints and anatomical axes.

Kinematics of the thorax and pelvis during accelerated sprinting.

BACKGROUND: This study aimed to describe changes in thoracic and pelvic movements during the acceleration phase of maximal sprinting, and to clarify which kinematic variable relates to better accelerated sprinting performance. METHODS: Twelve male sprinters performed 60-m sprints, during which three-dimensional step-to-step changes in thoracic and pelvic angles, as well as the trunk quasi-joint angle, were obtained throughout a 50-m distance. RESULTS: The patterns of thoracic and pelvic movements were maintained throughout the entire acceleration phase, although the phase profiles of the relative movements between the thorax and pelvis in three planes differed. Increase in peak thoracic and pelvic tilt angles terminated (-10.3° and 3.2° from the vertical line) and trunk extension range (≈21.7°) decreased from the 13th-15th steps. Moreover, thoracic and pelvic obliquity angles decreased from 15.3° and 8.8°, and conversely, rotation angles increased to 23.5° and plateaued (≈16°), during the entire acceleration phase. Moreover, smaller inclination of the thorax and deeper inclination of the pelvis, smaller rotations of the pelvis and trunk quasi-joint and greater thoracic obliquity during the initial section (to the 4th step), deeper inclination of the pelvis during the middle section (to the 14th step), and smaller trunk torsion and thoracic obliquity during the final section in the entire acceleration phase of sprinting were associated with increases in running speed. CONCLUSIONS: The results suggest that sprint acceleration toward maximal speed is not performed with only proportional increases in magnitudes of trunk movements, and important factors for better sprint acceleration performance alter with increasing running speed.

Alteration of swing leg work and power during human accelerated sprinting.

This study investigated changes in lower-extremity joint work and power during the swing phase in a maximal accelerated sprinting. Twelve male sprinters performed 60 m maximal sprints while motion data was recorded. Lower-extremity joint work and power during the swing phase of each stride for both legs were calculated. Positive hip and negative knee work (≈4.3 and ≈-2.9 J kg-1) and mean power (≈13.4 and ≈-8.7 W kg-1) during the entire swing phase stabilized or decreased after the 26.2±1.1 (9.69±0.25 m s-1) or 34.3±1.5 m mark (9.97±0.26 m s-1) during the acceleration phase. In contrast, the hip negative work and mean power during the early swing phase (≈7-fold and ≈3.7-fold increase in total), as well as the knee negative work and power during the terminal swing phase (≈1.85-fold and ≈2-fold increase in total), increased until maximal speed. Moreover, only the magnitudes of increases in negative work and mean power at hip and knee joints during the swing phase were positively associated with the increment of running speed from the middle of acceleration phase. These findings indicate that the roles of energy generation and absorption at the hip and knee joints shift around the middle of the acceleration phase as energy generation and absorption at the hip during the late swing phase and at the knee during early swing phase are generally maintained or decreased, and negative work and power at hip during the early swing phase and at knee during the terminal swing phase may be responsible for increasing running speed when approaching maximal speed.

Differences in take-off leg kinetics between horizontal and vertical single-leg rebound jumps.

This study aimed to clarify the differences between the horizontal single-leg rebound jump (HJ) and vertical single-leg rebound jump (VJ) in terms of three-dimensional joint kinetics for the take-off leg, while focusing on frontal and transverse plane movements. Eleven male track and field athletes performed HJ and VJ. Kinematic and kinetic data were calculated using data recorded with a motion capture system and force platforms. The hip abduction torque, trunk lateral flexion torque (flexion for the swing-leg side), hip external and internal torque, trunk rotational torque, and the powers associated with these torques were larger when performing HJ because of resistance to the impact ground reaction force and because of pelvic and posture control. Pelvic rotation was noted in HJ, and this was controlled not only by the hip and trunk joint torque from the transverse plane but also by the hip abduction torque. Therefore, hip and trunk joint kinetics in the frontal and transverse plane play an important role in a single-leg jump, regardless of the jumping direction, and may also play a more important role in HJ than in VJ.

Development of maximal speed sprinting performance with changes in vertical, leg and joint stiffness.

BACKGROUND: This study aimed to clarify the changes in stiffness variables when maximal speed sprinting performance was developed through long-term training. METHODS: Nine well-trained male athletes performed maximal effort 60-m sprints before and after the completion of six months of winter training. In both experiments, sprinting motion at maximal speed was recorded with a high-speed camera and simultaneously ground reaction force (GRF) was measured. Spatiotemporal and stiffness variables were then calculated. RESULTS: Sprinting speed was significantly developed (P=0.001) through longer step length (P=0.049). While the leg stiffness did not change (from -539±126 to -558±180 N/kg/m) (P=0.686), the vertical stiffness significantly increased (P=0.001) from -1507±346 to -2357±704 N/kg/m due to increase and decrease in vertical GRF and descent of whole body center of gravity, respectively. Moreover, whereas knee joint stiffness remained constant (from -0.228±0.080 to -0.213±0.084 Nm/kg/°) (P=0.448), ankle joint stiffness was significantly developed (P=0.002) from -0.165±0.031 to -0.210±0.032 Nm/kg/° due to a respective increase and decrease in ankle plantarflexion moment and ankle dorsiflexion angle. CONCLUSIONS: The results demonstrate that the development of maximal speed sprinting performance through longer step length is accompanied by increases in vertical and ankle joint stiffness, and this shows the importance of vertical and ankle stiffness for improving maximal speed sprinting performance. Findings of this study may assist with the planning of training programs for athletes.

Kinematics of transition during human accelerated sprinting.

This study investigated kinematics of human accelerated sprinting through 50 m and examined whether there is transition and changes in acceleration strategies during the entire acceleration phase. Twelve male sprinters performed a 60-m sprint, during which step-to-step kinematics were captured using 60 infrared cameras. To detect the transition during the acceleration phase, the mean height of the whole-body centre of gravity (CG) during the support phase was adopted as a measure. Detection methods found two transitions during the entire acceleration phase of maximal sprinting, and the acceleration phase could thus be divided into initial, middle, and final sections. Discriminable kinematic changes were found when the sprinters crossed the detected first transition-the foot contacting the ground in front of the CG, the knee-joint starting to flex during the support phase, terminating an increase in step frequency-and second transition-the termination of changes in body postures and the start of a slight decrease in the intensity of hip-joint movements, thus validating the employed methods. In each acceleration section, different contributions of lower-extremity segments to increase in the CG forward velocity-thigh and shank for the initial section, thigh, shank, and foot for the middle section, shank and foot for the final section-were verified, establishing different acceleration strategies during the entire acceleration phase. In conclusion, there are presumably two transitions during human maximal accelerated sprinting that divide the entire acceleration phase into three sections, and different acceleration strategies represented by the contributions of the segments for running speed are employed.

Determinants of the abilities to jump higher and shorten the contact time in a running 1-legged vertical jump in basketball.

This study was conducted to obtain useful information for developing training techniques for the running 1-legged vertical jump in basketball (lay-up shot jump). The ability to perform the lay-up shot jump and various basic jumps was measured by testing 19 male basketball players. The basic jumps consisted of the 1-legged repeated rebound jump, the 2-legged repeated rebound jump, and the countermovement jump. Jumping height, contact time, and jumping index (jumping height/contact time) were measured and calculated using a contact mat/computer system that recorded the contact and air times. The jumping index indicates power. No significant correlation existed between the jumping height and contact time of the lay-up shot jump, the 2 components of the lay-up shot jump index. As a result, jumping height and contact time were found to be mutually independent abilities. The relationships in contact time between the lay-up shot jump to the 1-legged repeated rebound jump and the 2-legged repeated rebound jump were correlated on the same significance levels (p < 0.05). A significant correlation for jumping height existed between the 1-legged repeated rebound jump and the lay-up shot jump (p < 0.05), although none existed for jumping height between the lay-up shot jump and both the 2-legged repeated rebound jump and countermovement jump. The lay-up shot index correlated more strongly to the 1-legged repeated rebound jump index (p < 0.01) when compared to the 2-legged repeated rebound jump index (p < 0.05). These results suggest that the 1-legged repeated rebound jump is effective in improving both contact time and jumping height in the lay-up shot jump.