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.

Athletes often experience short-term training cessation because of injury, illness, post-season vacation, or other reasons. Limited information is available about the effect of short-term (less than four weeks) training cessation on muscle strength in athletes. Sprinting athletes must maintain knee extension and flexion strength to reduce the risk of sprint-type hamstring strain injury. This study aimed to identify whether and to what extent knee extension and flexion torque in concentric and eccentric contractions is reduced by two weeks of training cessation in sprinters. Before and after the training cessation, maximal voluntary isokinetic knee extension and flexion torque in slow and fast concentric (60 and 300°/s) and slow eccentric (60°/s) contractions were assessed in 13 young male highly trained sprinters (average World Athletics points = 978). Knee flexion torque during the bilateral Nordic hamstring exercise (NHE) was also measured. After the training cessation, isokinetic concentric at 300°/s and eccentric torque were significantly reduced in both knee extension and flexion. There was no difference in the magnitude of reduction between isokinetic knee extension and flexion torques in all conditions. The relative changes were more notable in eccentric (-15.0%) than in concentric contraction at 60°/s (-0.7%) and 300°/s (-5.9%). Knee flexion torque during the NHE also declined (-7.9% and -9.9% in the dominant and non-dominant legs, respectively). There was no significant correlation between the relative reductions in isokinetic knee flexion torque and knee flexion torque during the NHE. The findings suggest that sprinters and their coaches should focus on recovering fast concentric and slow eccentric knee extension and flexion strength after two weeks of training cessation.

Yamashita, D, Asakura, M, Ito, Y, Yamada, S, and Yamada, Y. Physical characteristics and performance of Japanese top-level American football players. J Strength Cond Res 31(9): 2455–2461, 2017—This study aimed to compare the physical characteristics and performance between top-level nonprofessional football players in Japan and National Football League (NFL) Combine invited players and between top-level and middle-level players in Japan to determine the factors that enhance performance in international and national competitions. A total of 168 American football players (>20 years) in Japan participated in an anthropometric (height and weight) and physical (vertical jump, long jump, 40-yard dash, pro-agility shuttle, 3-cone drill, and bench press repetition test) measurement program based on the NFL Combine program to compete in the selection of candidates for the Senior World Championship. All players were categorized into 1 of the 3 position groups based on playing position: skill players, big skill players, and linemen. Japanese players were additionally categorized into selected and nonselected players for the second tryout. The NFL Combine candidates had significantly better performance than selected Japanese players on all variables except on performance related to quickness among the 3 position groups. Compared with nonselected players, selected Japanese skill players had better performance in the 40-yard dash and bench press test and big skill players had better performance in the vertical jump, broad jump, and 40-yard dash. Selected and nonselected Japanese linemen were not different in any measurements. These results showed the challenges in American football in Japan, which include not only improving physical performance of top-level players, but also increasing the number of football players with good physical performance.

Purpose : Sport-physiology and -performance research often relies on group designs that compare experimental and control groups and/or preintervention and postintervention results. This commentary highlights the key elements of a high-quality case study and provides clear guidelines for readers and authors of the International Journal of Sports Physiology and Performance . We propose 4 essential components. First, case studies should offer relevant and original insights by tackling novel issues and defining a clear purpose. Second, they must employ rigorous methodology, encompassing careful participant selection, comprehensive data collection from diverse sources (eg, interviews, surveys, physiological tests, training diaries, competition data), and deliberate data analysis that explicitly addresses factors influencing performance changes. Third, they should be well structured and engagingly presented to reach both academic and practical audiences. Finally, bridging the science–practice gap is vital, requiring and strengthening collaboration between researchers and practitioners to enable data-driven decision making and spark new hypotheses. Conclusions : Although case studies traditionally rank low in the research evidence hierarchy, high-quality examples can significantly bridge the gap between research and practice. By working closely with the sporting community and strategically sharing findings, case studies can enhance evidence-based training strategies and amplify the real-world impact of sport science.

This study aims to identify the relationship between jump height and the kinetic and kinematic parameters of the hip, knee, and ankle joints during countermovement jump (CMJ) in elite male athletes. Sixty-six elite male athletes from various sports (strength and power, winter downhill, combat, ball game, and aquatic) performed maximal effort CMJs with hands and arms crossed against their chests on force platforms. Jumping motion in the sagittal plane was recorded using video analysis and the peak torque, power, and angular velocity of the right hip, knee, and ankle joints were calculated during the propulsive phase. Correlations between the CMJ height and kinetic and kinematic parameters were investigated using Pearson's product-moment coefficient (r) and Spearman's rank correlation coefficient (ρ). CMJ height was highly correlated with peak hip power (ρ = 0.686, p < 0.001) and peak knee angular velocity (r = 0.517, p < 0.001), and moderately correlated with peak hip angular velocity (r = 0.438, p < 0.001) and peak hip torque (r = 0.398, p = 0.001). These results indicate that notable hip torque and power can contribute to increased angular velocity in both the knee and hip joints, ultimately increasing the CMJ height in elite male athletes.

Aims: The Academic Research Consortium (ARC) has proposed international criteria to standardize the definition of high bleeding risk (HBR) in patients undergoing percutaneous coronary intervention (PCI). In this context, Japan has also established its own guidelines, that is, the Japanese version of HBR (J-HBR) criteria. However, the J-HBR criteria have not been fully validated, especially in patients with acute myocardial infarction (MI). Methods: This bi-center registry included 1079 patients with acute MI undergoing primary PCI in a contemporary setting. Patient bleeding risks were evaluated using the ARC-HBR and J-HBR criteria. The primary endpoint was rates of major bleeding events (Bleeding Academic Research Consortium type 3 or 5) at 1 year. Results: Of the 1079 patients, 505 (46.8%) and 563 (52.2%) met the ARC-HBR and J-HBR criteria, respectively. Patients who met the J-HBR criteria were found to have a higher rate of major bleeding events at 1 year than those who did not (12.8% vs. 3.3%, p＜0.001). When patients were scored and stratified using the J-HBR major and minor criteria, risks of major bleedings were progressively increased with the increase in the number of J-HBR criteria. In the receiver operating characteristic curve analysis, the ARC-HBR and J-HBR significantly predicted subsequent major bleedings after PCI, with ARC-HBR having greater predictive ability than J-HBR. Conclusions: More than half of the patients with acute MI undergoing primary PCI in Japan met the J-HBR criteria. Although the J-HBR criteria successfully identified patients who were likely to develop major bleeding events after primary PCI, the superiority of J-HBR to ARC-HBR in predicting bleeding outcomes warrants further investigation.