EFFECT OF LEG STIFFNESS DURING REBOUND JUMP ON SPRINT RUNNING KINEMATICS AND KINETICS

We investigated the relationship between stiffness in rebound jump (RJ) and kinematics and kinetics of the support- and swing-leg in sprint running (SP). We included 13 male track and field athletes performing maximal effort SP and RJ. During the support phase, kinematics, kinetic, and leg stiffness parameters were calculated using a force platform and data from a high-speed video camera that recorded movement in the sagittal plane. A significant correlation was observed between SP and RJ for stiffness (r = 0.683). In SP, stiffness was significantly correlated with contact time (r = -0.659), mean joint torque at the ankle (r = 0.703) and knee (r = -0.726) joints, CG (center of gravity) -toe distance (r = -0.818), and the swing-leg angle (r = -0.676) at touch down. Based on our results, kinematics and kinetics correlated with stiffness in SP are affected by RJ stiffness

THE DIFFERENCES BETWEEN HORIZONTAL AND VERTICAL DIRECTION DURING A SINGLE-LEG REBOUND JUMP: OBTAINED USING THREE-DIMENSIONAL MOTION ANALYSIS

The purpose of this study was to clarify the differences between single-leg rebound jump for horizontal direction (HSJ) and vertical direction (VSJ) in terms of three-dimensional joint kinetics for the take-off leg focused on frontal plane movement. Eleven male track and field athletes were performed the HSJ and VSJ. Kinematics and kinetics data were recorded using Vicon T20 system (250 Hz) and force platforms (1000 Hz). In HSJ, as compared to VSJ, the joint kinetics characteristics are as follows: 1) the hip abduction torque and torque power around the adduction-abduction axis are larger; and 2) the trunk lateral flexion torque and torque power around the adduction-abduction axis are larger. Therefore, the hip adduction-abduction and trunk lateral flexion-extension movement plays an important role in a single-leg jump. Additionally, this is pronounced in HSJ as compared to VSJ

THE DIFFERENCES BETWEEN DOUBLE AND SINGLE LEG TAKEOFF ON JOINT KINETICS DURING REBOUND-TYPE JUMP

The purpose of this study was to identify the differences between double and single leg takeoff on joint kinetics during a rebound-type jump. Twelve male track and field athletes performed repeated rebound-type jumps with double legs (DRJ) and a single leg (SRJ). Kinematics and kinetics data were recorded using a high-speed video camera (300 Hz) and force platforms (1000 Hz). The negative and the positive values of the joint torque power about the ankle joint were significantly lower in DRJ than in SRJ. However, the mean joint extension torque, and the negative value of the joint torque power about the hip joint was larger in SRJ than in DRJ. It is suggested that the joint kinetics characteristics, in SRJ as compared to DRJ, reveals a relatively large joint torque and torque power about the hip joint

THE COMPARISON TO THE CHARACTERISTICS OF THREE-DIMENSIONAL JOINT KINETICS BETWEEN SINGLE LEG AND DOUBLE LEG REBOUND JUMP

The purpose of this study was to clarify the differences between the SRJ and DRJ in terms of three-dimensional joint kinetics for the takeoff leg. Twenty male track and field athletes were performed repeated rebound jump with single leg (SRJ) and double leg (DRJ). Kinematics and kinetics data were recorded using Vicon T20 system (250 Hz) and force platforms (1000 Hz). When comparing a SRJ to a DRJ, the characteristics of the former are as follows: 1) the jump height by a single leg is significantly higher because of the larger hip joint work around the extension-flexion, especially on the abduction-adduction axes; 2) the hip extension and abduction torque is larger; and 3) in the SRJ, the hip abduction torque is larger than the hip extension torque. Therefore, the joint kinetics of the SRJ is characterized by the large hip abduction torque, in addition to the large hip extension torque

SPRINT STEP-TYPE SPECIFIC CHARACTERISTICS OF ANTHROPOMETRIC AND KINEMATIC VARIABLES IN SPRINTING ACCELERATION

The purpose of this study was to compare the anthropometric and the kinematic characteristics during the acceleration phase between stride frequency (SF)-type and stride length (SL)-type sprinters. Seventeen sprinters participated in this study. The maximal 60-m sprints and anthropometric measures were obtained from subjects. Two sprints were recorded by using high-speed cameras. Sprint velocity, SL, SF and their underlying kinematic variables were calculated. Cluster analysis was used to classify the subjects into the SF or SL -type groups (step-type) as indicated by the ratio of the SF and SL at maximum velocity. The SF-type group showed shorter lower limbs length, flight time, lower the height of center of mass at takeoff, smaller swing motion and faster forward rotation of the shank and foot segments than the SL-type group. This study showed the noticeable differences between SFtype and SL-type sprinters were not only in swing motion but also in push-off motion

TYPE-SPECIFIC STEP CHARACTERISTICS OF SPRINTERS DURING ACCELERATION PHASE OF 100-M RACE

The purpose of this study was to show the type-specific step characteristics during acceleration phase (0?30 m) of a 100-m race. Fifty-nine male varsity sprinters (10.68 ± 0.22 s) were recorded running in 100-m races using 10 high-speed cameras, and step variables in 0?30 m and maximum speed phase (MSP, 30?60 m) were calculated. Cluster analysis was used to classify the subjects into the step-frequency (SF) or -length (SL) reliant group (i.e., type-specific) as indicators for the ratio of the SF and SL in the MSP. Then, each group was divided into two sub-groups according to the mean speed in MSP (good and poor sprinters). As a result, the sprinters were classified into SL-, SF-, and Mid-groups. In SL-group, good sprinters showed a longer SL from the 7th step to MSP than the poor sprinters. In SF-group, good sprinters showed a higher SF from the 7th step to MSP than the poor sprinters

EFFECTS OF STRETCH-SHORTENING CYCLE DURING TRUNK-TWIST EXERCISE USING DIFFERENT LOADS

The purpose of this study was to investigate the effects of stretch-shortening cyde (SSC) movement during bunk-twist and whether the effects change on increasing the loads by using a special trunk-twist machine. Twenty-one male college students performed trunktwist exercise with 3 loads. Participants performed this exercise for each load by using SSC and not using SSC (CON). Kinematic and kinetic data were recorded using Vimn system (250 Hz) and force platform (1,000 Hz). The following effects of SSC for this exercise were observed: (1) peak bar angular velocity was not potentiated by SSC, but SSC contributed to the acceleration of bar angular velocity and (2)for heavy loads, SSC did not affect mean angular velocity of the bar, upper trunk and pelvic rotation. Moreover, peak joint torque power of trunk-twist significantly decreased with heavy loads

THE EFFECT OF INCREASING JUMP STEPS ON THE TAKE-OFF LEG IN BOUNDING

The purpose of this study was to clarify the effect of increasing jump steps in bounding in terms of three-dimensional joint kinetics for the take-off leg. Eleven male track and field athletes performed horizontal bounding from the standing posture. Kinematic and kinetic data were recorded using a Vicon T20 system (250 Hz) and force platforms (1,000 Hz). As jump steps increased, the joint kinetics characteristics are as follows: 1) ankle plantar flexion torque and knee extension torque and power increased, but hip extension torque and power did not increase; and 2) hip external torque and power (negative and positive) increased, particularly hip abduction torque and power. Therefore, in bounding initiated from the standing posture, ankle and knee joint kinetics from the sagittal plane and 3dimensional hip joint kinetics increased, particularly on hip adduction-abduction axis

DEVELOPMENT OF A NEW ASSESSMENT METHOD FOR THE REBOUND JUMP TEST

We have proposed a new assessment method using joint kinetics and performance variables in the rebound jump (RJ) test. Twenty-seven male jumpers performed the RJ test. The Quick Motion Analysis System (jointly developed with DKH Inc.) was used to measure joint torque, power, and work of the three lower limb joints in real time, with high precision. High-performance jumpers had high performance values and showed a significantly large amount of joint work in the ankle and hip joints on the RJ test. Comparison of the work of the three lower limb joints confirmed a conflicting relationship between the hip and knee joints and that of the ankles, indicating that this new system is useful for evaluating joint kinetics of the three lower limb joints and may contribute greatly to the assessment of muscle strength and power

DEVELOPMENT OF MULTISTEP DROP JUMP TEST BY USING DIFFERENT DROP HEIGHTS

We used different drop heights to evaluate the drop jump (DJ) test in elite athletes. Male jumpers (n=10) performed the test at 0.3, 0.6, 0.9, and 1.2 m. Jumping motions in the sagittal plane and the ground reaction force were recorded using a high-speed camera and force platform, respectively. The amount of negative work by 3 lower extremity joints increased with increased drop height of the DJ test, mainly at the hip joint. There were different performance patterns on the DJ test and lower extremity power output with an increased drop height according to individual characteristics of elite jumpers, compared with the average pattern. Jump performance was correlated with the DJ index at DJ1.2 and the decreased rate of the index from DJ0.3 to DJ1.2. Thus, to evaluate elite jumpers’ performance, various height ranges including a higher drop height should be used