Flight time is widely used to calculate jump height because of its simple and inexpensive application. However, this method is known to give different results than the calculation from vertical velocity at takeoff. The purpose of this study is to quantify the effect of postural changes between takeoff and landing on the jump height from flight time. Twenty-seven participants performed three vertical jumps with arm swing. Three-dimensional coordinates of anatomical landmarks and the ground reaction force were analyzed. Two methods of calculating jump height were used: (1) the vertical velocity of the whole-body center of mass (COM_wb) at takeoff and (2) flight time. The jump height from flight time was overestimated by 0.025 m compared to the jump height from the takeoff velocity (p < 0.05) due to the lower COM_wb height at landing by −0.053 m (p < 0.05). The postural changes in foot, shank, and arm segments mainly contributed to decreasing the COM_wb height (−0.025, −0.014, and −0.017 m, respectively). The flight time method is reliable and had low intra-participant variability, but it cannot be recommended for a vertical jump when comparing with others (such as at tryouts) because of the potential “cheating” effect of differences in landing posture.

We aimed to elucidate spatiotemporal and kinetic determinants of sprint acceleration performance in soccer players. Thirty-seven male soccer players performed 60-m sprints. The spatiotemporal variables and ground reaction impulses were calculated over a 50-m distance. When controlling the influence of stature and body mass, change in running speed was correlated with the step length at the 1st–4th step section (r = 0.695), step frequency from the 9th to 20th step sections (r = 0.428 to 0.484), braking impulse during the 17th–20th step section (r = 0.328), propulsive impulse from the 1st to 8th step sections (r = 0.738 and 0.379), net anteroposterior impulse for all step sections (r = 0.384 to 0.678), and vertical impulse from the 9th–12th step section and thereafter (r = −0.355 to −0.428). These results confirmed that an effective acceleration is probably accomplished by a greater step length originated in greater propulsive impulse during the initial acceleration phase (to the 8th step), a higher step frequency through smaller vertical impulse and smaller braking impulse during the middle and later acceleration phases (from the 9th step), as well as greater net anteroposterior impulse during the entire acceleration phase.

TrackMan, a device used to measure the kinematics of a ball in flight, has recently been used for research and coaching purposes in tennis, and the number of studies on this device is expected to increase. This study is focused on verifying the accuracy of TrackMan; three participants performed services with various velocities and angular velocity combinations. TrackMan and a proven method based on computer vision were used to measure the speed, spin rate, and spin axis of the ball. The results obtained using each method were compared using regression analysis, intraclass correlation coefficients, and Bland–Altman analysis. The speed and spin rate of the two methods agreed well; the degree of error would not be problematic in practical applications. However, TrackMan underestimated the speed if it was unable to detect the hitting position. The spin axis measured by TrackMan was unstable under low spin rate conditions (<3000 rpm). Furthermore, the standard deviation of the spin axis measurement error exceeded the difference between the average slice and kick service spin axes reported in the previous study, so the spin axis measurement accuracy was very low for research purposes, even when the spin rate was above 3000 rpm. For those who are aware of the existence of outliers, TrackMan can be useful for coaching because it provides instant feedback. Similarly, the measured rotational speed and spin rate could be used in the study.

This study aimed to comprehensively demonstrate support leg joint kinetic determinants of maximal speed sprint performance. Ground reaction forces and marker coordinates attached to the body were measured in the maximal speed phase from 44 male sprinters. Then, three-dimensional leg joint torque, angular velocity and power were calculated. Greater maximal running speed (9.47 +/- 0.32 m/s) was correlated with greater mean hip extension (r = 0.354, p = 0.018) and flexion (r = -0.322, p = 0.033) and ankle plantar flexion torques (r = 0.464, p = 0.002), as well as greater ankle plantar flexion torque from 30% to 70% of the support phase (p < 0.001). Greater maximal running speed was associated with greater mean hip extension (r = 0.386, p = 0.010) and smaller knee extension velocities (r = -0.426, p = 0.004). Regarding joint torque power, greater maximal running speed was associated with greater mean positive (r = 0.416, p = 0.005) and negative (r = -0.390, p = 0.009) hip flexion - extension powers and positive (r = 0.642, p < 0.001) and negative (r = -0.512, p < 0.001) ankle plantar - dorsi flexion powers. Moreover, greater maximal speed was correlated with greater positive and negative ankle plantar - dorsi flexion powers from 21% to 39% (p < 0.001) and from 56% to 80% (p < 0.001), respectively, during the support phase. Understanding the joint kinetics related to maximal running speed will improve technical considerations and strength training direction for sprinters.

The purpose of this study was to identify the dynamic factors contributing to pelvis angular velocity about its longitudinal axis (pelvis axial angular velocity) during the golf swing. Thirty-one right-handed skilled golfers (handicap, 3.5 ± 1.8) performed swings with a driver. The kinematic and kinetic data were collected using an optical motion analysis system and two force platforms. The dynamic factors (i.e., joint torque, gravitational force, motion-dependent forces and inertia forces) contributing to pelvis axial angular acceleration were calculated. The present study revealed that the left (lead) hip flexor and adductor torques as well as the right (trail) hip extensor and abductor torques were identified as the main contributors to pelvis axial angular velocity. These hip joint torques contributed not synchronously but sequentially to the pelvis. Although the knee joint torques contributed little to pelvis axial angular velocity directly, the knee joint torques might support the generation of large hip joint torques by regulating joint postures. These findings indicate that the functional coordination of the lower limb segments as well as the magnitude of the joint torques play an important role in rotating the pelvis.